RHS Certificate III Principles of Plant Growth, Health and Applied Propagation


  • Develop your ability to describe the principles of plant taxonomy, structure, function and growth, the management of plant health, and plant propagation.
  • Get a unique qualification; accredited in the UK, awarded by the Royal Horticultural Society; recognised internationally
  • Be more successful in your career, as a gardener, nurseryman or gardens manager


This is one of several new RHS Qualifications being phased in to replace older courses over the second half of 2010.

Duration: 200 hours

Prerequisite: RHS Certificate II in Horticulture, an Australian level 3 certtificate in horticulture or any ACS Certificate in Horticulture (or equivalent)


Lesson Structure

There are 15 lessons in this course:

  1. Taxonomic Classification of Plants
  2. Structure and Function of Cells and Tissues
  3. Role of Flowers and Fruit
  4. Photosynthesis, Respiration, and Movement of Water
  5. Effects of Tropisms and Plant Growth Regulators
  6. Physical Properties of Growing Media
  7. Chemical Properties of Growing Media and Role of Air and Water
  8. Biological Processes in Growing Media
  9. Nutrients and Plant Growth
  10. Organic Techniques and Soil Management
  11. Plant Pests, Diseases and Disorders Part A
  12. Plant Pests, Diseases and Disorders Part B
  13. Regulation of Chemicals and Storage Procedures
  14. Seed Propagation
  15. Vegetative Propagation

Each lesson culminates in an assignment which is submitted to the school, marked by the school's tutors and returned to you with any relevant suggestions, comments, and if necessary, extra reading.


  • Demonstrate knowledge of the major divisions of the plant kingdom and an understanding of the taxonomic hierarchy and its relevance to horticultural practice.
  • Identify and describe the different types of plant cells and tissues, their structure, and function.
  • To understand the role and function of the reproductive parts of the plant and the seed in the plant lifecycle.
  • Understand the mechanism and role of photosynthesis and respiration in the metabolism of plants, the role of water in the plant, and the movement of water, solutes, and assimilates through the plant.
  • To develop an understanding of the effects of tropisms and other plant movements on growth and development.
  • Understand the physical properties of growing media and their significance in relation to plant growth.
  • To understand basic chemistry of soils and other growing media, and the relationship between their air and water content and plant growth.
  • To understand the role of living organisms in the biological processes of soils and other growing media.
  • To understand how nutrients affect plant growth and describe a range of fertilisers and their applications.
  • To determine appropriate management programs for different soils in horticultural situations.

Prerequisite: RHS Certificate II in Horticulture or equivalent

Duration -200 hours


To obtain the certificate, awarded by the RHS in England, the student needs to sit and pass written exams conducted under supervision, and assessed by the RHS.

  • Exams can be arranged to be sat anywhere in the world.
  • Exams are offered twice annually; in February and June. A separate fee applies for exams; set by and paid to the RHS.
  • A network of exam centres are located across the UK for students located in the UK
  • For students located elsewhere; a provision is made for exams to be conducted "under arrangements for exceptional supervision".

This is one of several new RHS Qualifications being phased in to replace older courses over the second half of 2010.

The older courses can still be studied with ACS, but there will be cut off dates on their accreditation; and the possibility of sitting an RHS exam for the older qualification may be missed. Opportunities will be made available to upgrade from the older courses to the new qualifications, irrespective.



The following is an example "parts" out of a typical lesson from this course (Not the complete lesson):


To understand how nutrients affect plant growth and describe a range of fertilisers and their applications.

This section looks at a number of nutrient problems that may occur with soils in horticulture, and how you can go about rectifying each problem.


Soil nutrition is, to some extent, indicated by the vigour of the plants growing in a soil. If inadequate nutrients are present in the soil, plant growth is stunted. This effect is subtle and not usually noticed until it becomes severe. It can be that nutrient requirements drop to as low as 30% of optimum levels before deficiency symptoms, such as discolouration, appear in the leaves. By this time, the overall growth rate and general health of the plant has been affected significantly.

Every plant variety has its own unique set of nutrient requirements. Some plants need more iron and less phosphorus than others, while others need more phosphorus and less potassium. There are tens of thousands of different 'ideal' nutrient conditions, one for each different plant.

We can get a guide to the individual requirements of a particular plant variety by chemically analysing the nutrients found to make up the leaf tissue of a very healthy specimen of that particular variety. Analysis of unhealthy plants can also be carried out and compared with the analysis of healthy plants. This can tell us what nutrients are missing in the unhealthy plants.

The following are the normal range of each of each nutrient found in plant tissue:

N    2-5%
P     0.2-0.5%
K     0.5-5.0%
Mg   0.3-0.6%
S      0.2-0.5%
Ca    0.5-2.0%
Fe    50-150 ppm
Zn    15-100 ppm
Mn   50-100 ppm
Bo    25-100 ppm
Cu    5-15 ppm
Mo   0.1-1ppm

Before we go on to consider plant nutrient deficiencies it is important to gain an understanding of what the significant plant nutrients are, and how they are utilised by the plant for growth.


Research in the past has shown that at least 50 different elements may be used by plants. This does not mean all of these are necessary to all plants though. The elements usually considered necessary to the life of all plants include:

Carbon(C), Oxygen (O), and Hydrogen (H)

These elements are required by all living things as the basis of all organic molecules.

A number of other elements are required by plants and these are generally divided into two groups the MAJOR elements or MACRONUTRIENTS, and the MINOR elements or MICRONUTRIENTS. There are six macronutrients of plants. They are: Nitrogen (N), Phosphorus (P), Potassium (K), Magnesium (Mg), Calcium (Ca), and Sulphur (S).

The micronutrients include all those elements taken up by plants in only small amounts. The number and importance of elements in this group will vary according to the type of plant and the way it is used by the plant. It is also be possible to include a third group of elements - non toxic elements which are taken up but not required by plants. This group is estimated to be very large and includes Gold (Au), but is of no importance to our discussions here. The micronutrients, also called 'trace elements' include: Iron (Fe), Zinc (Zn), Manganese (Mn), Copper (Cu), Boron (B), Chlorine (Cl), Molybdenum (Mo) and Chlorine (Cl).

Some elements are more important for human nutrition than for the plant. Some examples include Cobalt (Co), Chromium (Cr) and Iodine (I). Other elements are only needed by certain types of plants, or their requirements are uncertain. These include Sodium (Na), Aluminium (Al), Silicon (Si), and Selenium (Se).


Nitrogen, phosphorus, potassium, calcium, magnesium and sulphur are needed by plants in much larger quantities than any other elements (except carbon, oxygen and hydrogen). Most soils have ample supplies of calcium and magnesium hence fertilisers which are used in horticulture are usually almost completely made up of nitrogen, phosphorus and potassium foods. (The one exception is in hydroponics where it becomes necessary to add large amounts of magnesium and calcium).

Nitrogen is the element essential for good foliage and stem growth. When there is a flush of rapid growth, nitrogen requirements become particularly high.

Adequate nitrogen is essential for good fruiting and other plant processes, as it is required in the synthesis of proteins and enzymes in every living cell, though it is more closely related to the green growth. Nitrogen is obtained via the roots from in the soil solution (and to a degree from the atmosphere by legumes).

Nitrogen fertilisers are applied to plants in the order to stimulate green, vegetative growth. Obvious situations to apply nitrogen would be on leafy vegetables, on young plants to stimulate faster growth, on lawns, and on plants grown for their foliage.

Symptoms of deficiency include stunted growth and general chlorosis, while toxicity is generally first noticed by a lush green overgrowth, with increased susceptibility to frosts, etc. and eventual collapse.

Nitrogen fertilisers include:

• Sulphate of ammonia (21% nitrogen)
• Blood and bone
• Sodium nitrate
• Calcium nitrate
• Potassium nitrate (34% nitrogen)
• Urea (46% nitrogen)

Adequate phosphorus is essential to maximise root development, for growth, and energy transfer. Deficiencies lead to poor fruiting and spindly growth. Other symptoms may include purplish tinting of leaves and poor seed set.

Lack of phosphorous is common in some soils (e.g. Australian soils), making it essential to fertilise well with phosphorous to achieve good growth with many types of crops. It should be remembered, however, that of any amount of phosphorus applied to the soil, only about 20% may be immediately available to the plant, the rest being released slowly over a period of time.

Some Australian native plants have adapted to low phosphorous soils to the extent that they can easily be harmed by fertilising with phosphorous (e.g. Grevillea spp.).

Good sources of phosphorous include:

• Superphosphate
• Monocalcium phosphate
• Shrimp waste
• Raw sugar waste
• Bone meal and other organic foods (including blood and bone)

Potassium is required by the plant in quite large amounts and is necessary to maintain cell turgor and the plant's water relations, controlling the opening of stomata, etc. Soils in dry areas usually have good reserves of potassium. It is very soluble and very mobile in the plant. It is known that good levels of Potassium are needed in particular, for flowering and fruiting. It is also very active in meristematic tissue, where it appears to behave in a similar way to calcium. Deficiency symptoms include marginal chlorosis of older leaves, low yields, weak stems and meristematic necrosis.

Good sources of potassium are:

• Potassium sulphate (sulphate of potash: 41.5% potassium)
• Potassium chloride (muriate of potash: 50% potassium)
• Wood ash and organic fertilisers (seaweed, straw, and most manures, etc.)

This is essential to chlorophyll formation and energy transfer processes. Developing fruit have a high requirement. Deficiencies are usually noted by interveinal chlorosis and stunting.
Fertilisers include:

• Dolomitic limestone (dolomite)
• Epsom salts

The main role of Calcium is in formation of pectic compounds of the middle lamella. It is not transportable in the phloem, where it is rapidly precipitated as Calcium Oxalate. Thus, symptoms of deficiency occur in active meristematic tissue as apical and marginal chlorosis of young shoots and leaves, as well as in developing fruits.

Calcium fertilisers include:

• Slaked lime
• Agricultural limestone
• Dolomite
• Gypsum

This element is not often deficient, as many forms of fertiliser are provided as sulphates. Also, toxicity is rare due to high tolerances in many plants. This, along with their solubility, is the reason for the use of sulphates in fertilisers. Sulphur is, however, very necessary for plant growth and a plant may require almost as much sulphur as it does magnesium. One of its main functions in the cell is the formation of disulphide bonds in protein molecules. These bonds are largely responsible for the tertiary structure of many proteins and so deficiency will deactivate them. When deficiency occurs it is usually noticed as chlorosis of the leaf veins (as opposed to the interveinal chlorosis of other nutrients).


Many of these are just as essential as the major elements but are not required in as large a quantity. Deficiency of a minor element can have just as devastating results as deficiency of a major one.

• Iron essential for the functioning of a number of accessory photosynthetic pigments (cytochromes, etc). Lack of the small amount of required iron will cause plant growth to cease and produce interveinal chlorosis in many plants. Iron deficiencies are more common than any other minor nutrient problem. Plants which commonly suffer iron deficiencies include: Banksia, Protea, Grevillea, Citrus, Azaleas, Daphne, etc. Iron can be fed to a plant by applying Iron Chelate, Iron Sulphate or even some old rusty nails.

• Zinc contributes to the manufacture of carbohydrates and proteins, by functioning as an activator of a number of enzyme reactions. It is a common deficiency in Australia. Fertiliser: Zinc Sulphate.

• Manganese necessary, but quantity varies greatly between species. Its functions are similar to those of zinc. Evergreens generally use more than deciduous. Fertiliser: Manganese sulphate.

• Copper very small quantities are needed, although it is known to be essential. Little is known of its function, but excess copper is known to be toxic, and, in some plants, causes an Iron deficiency. Fertiliser: Copper Sulphate.

• Molybdenum essential in nitrate reduction, a component of some enzymes, important in nitrogen fixation which occurs in the roots of legumes. Deficiency occurs more often on acid soils. Fertiliser: Ammonium molybdate.

• Boron may assist utilisation of calcium, may play a part in formation of cell walls, involved in cell division and essential to carbohydrate and nitrogen metabolism. Fertilisers: Borax or Boric acid.

• Chlorine this element is essential, but tolerances vary widely and the precise function of this element within the plant is still uncertain. There are no records of a plant needing to be fed chlorine, although toxicities are known, especially in tobacco and potatoes.

• Cobalt there is no direct proof that this is absolutely necessary in plants, though it does seem important to Nitrogen fixation in legumes. It is important to Human nutrition in the formation of certain compounds such as Vitamin B12. The amount of cobalt in plants can vary greatly.

• Silicon occurs in greater quantities in monocotyledons (e.g. Grasses, Iris, Lilies, Orchids etc). Silicon does improve the growth of some plants. Some say it is necessary in minute amounts, but this is by no means an established fact.

• Aluminium essential in some species only (e.g. Peas, corn, sunflower and some grasses). Over 10ppm is toxic. It can also help reduce the effects of phosphorus toxicity to some degree.

• Selenium is used in varying amounts by some species only.

• Sodium though not usually considered essential, sodium can replace potassium as a nutrient to a limited extent.


Most nutrients in the soil exist in the form of a salt (e.g. common table salt is sodium chloride, or a sodium salt). 'Total Salts' refers to the combined effect of all different types of salts in the soil. Individually salts might not have any effect, but combined they may be toxic to a plant. Excessive salt is often indicated by a whitish caking on the surface of the soil.


These begin with drying of the leaf margin - beginning at the tip of the leaf. This is followed by death of the tip and then marginal leaf burn. In severe cases leaves shrivel and whole branches suddenly wilt. Chemical laboratory analysis is needed to confirm the problem.

The only solution is to wash the salts out of the soil. In places with inadequate drainage this is next to impossible. The soil may be permanently damaged, unless some form of drainage system can be installed.


There are a number of soil conditions which can impact the availability and subsequent uptake of nutrients by plants.

1) pH
The ease with which nutrients are able to enter a plant is greatly affected by pH. Extremely acidic or alkaline soils can often stop the nutrients present being absorbed and used by the plant. The plant will suffer a nutrient deficiency, not because the required nutrient is not in the soil, but because the plant cannot take it up (i.e. it is not available). Excess acidity may create toxic soil conditions due to the increase in solubility of such elements as aluminium and manganese. Soils which are too basic may cause deficiencies of essential nutrients such as boron, iron, zinc and manganese.

The ideal pH for nutrient availability is different for each nutrient. A pH that makes iron very available will make calcium much less available. The only answer is to compromise go for a pH in the middle (6-6.5), where no element is so available as to become toxic and the amounts of others can be increased to compensate for any loss in availability. In this range soil microbe populations will increase making nitrogen and carbon available to plants. Generally speaking, macronutrients are less available in soils with a low pH and micronutrients are less available in soils with a high pH. The optimum pH values for nutrients are as follows:

Nitrogen 6 to 8            

Calcium 7 to 8.5

Phosphorus 6 to 7.5

Potassium 6 to 10

Magnesium 7 to 8.5

Sulphur 6 to 10

Iron 4 to 6

Manganese 5 to 6.5

Boron 5 to 7

Copper/Zinc 5 to 7

2) Soil Organisms

Earthworms are important in both garden soil and compost. A plentiful supply of earthworms in your soil is a good indication of a healthy soil. As earthworms work, they pass soil through their bodies, mixing layers of soil and leaving loosely packed material behind. Earthworms’ burrows improve aeration and water infiltration into the soil. Vertical burrows allow air further down into the soil and encourage nutrient recycling by micro-organisms at those deeper levels. The inside of worm burrows are lined with compounds that are high in nutrients.

Along with micro organisms, they also help to break down organic matter, turning it into humus which is an important soil conditioner. Worm faeces, known as castings, have a higher nutrient content than the soil they ingested. Earthworms are also known to secrete a substance which promotes plant growth.

Various fungi are often found to be associated with particular types of plants. These fungi are found to have a special relationship with tree roots forming a structure called mycorrhiza. Most healthy trees will tend to show this condition. The fungus appears to get nutrition from the tree, whilst not harming the tree itself. The presence of the fungi can assist in the tree’s growth by increasing the tree root’s absorptive area. Eventually infected roots are shed by the tree and the fungus utilises them as food. The presence of michorizza can also protect the roots from invasion by harmful nematodes.

Many mycorrhiza live in a symbiotic (mutually dependent) relationship to a plant, many of which are legumes such as peas, beans, lupins, and wind shelter trees like she-oaks (Casuarina).

There are many other species of fungi some of which are single celled yeasts and others which appear in colonies with the typical thread-like appearance. Many of them decompose organic matter which can then be used by plants. They are often the first to break down large pieces of matter commencing the whole decomposition process. Some help plants by releasing growth hormones whereas others release antibiotics - a well known one being penicillin.

There are many different species of bacteria and their main benefit to plants is improving nutrient availability. Some release hormones which stimulate plant root growth.

Some plants, such as the legumes, have the ability to fix atmospheric nitrogen into the soil. What this means is that the plant is able to convert nitrogen in the air into a compound that can be used in the soil by plants. This is carried out by micro organisms, such as Rhizobium bacteria, that live in swellings on the roots of legumuminous plants. These plants can be a valuable source of nitrogen to a soil.

Other species of bacteria are able to fix nitrogen available for plant use without having a symbiotic relationship with particular plants. Bacteria also combat root diseases, detoxify the soil, improve nutrient solubility, and ameliorate soil structure. Some species release nitrogen, phosphorous, sulphur and trace elements through decomposition of organic matter whereas others decompose minerals to provide magnesium, calcium, iron and potassium.

Actinomycetes look like fungi due to their thread-like appearance but are also bacteria which decompose organic matter into humus and release nutrients in the process. They release antibiotics that combat root diseases.

These include centipedes, millipedes, slugs and snails. They generally consume larger decaying organic matter and some bury matter where it becomes accessible to micro-organisms. Their nutrient rich faeces are decomposed further by bacteria and fungi.

Whilst all algae photosynthesise their own food the blue-green species also release nutrients which become available to plant roots, and the slime they produce can enhance soil structure by binding particles together.

Most nematodes are beneficial to plants, only a few species are parasitic. They consume bacteria, fungi, algae, protozoa and decaying organic matter and so aid in the decomposition process.

Like nematodes, protozoa are predatory and largely eat other microbes. By consuming bacteria they speed up the release of nitrogen for plant availability.

All these various soil organisms play a role in the soil's ecosystem and their actions not only release nitrogen but also vitamins, amino acids, antibiotics, sugars, and so on. There is a balance between the populations of these organisms in healthy fertile soil.

3) Soil Texture

As we have learned previously, soil texture is determined by the relative amounts of sand silt, clay and organic matter in a soil. Soil texture not only affects the movement of air through the soil, but also the movement of water and nutrients.

Soils with high organic matter content and clay soils hold nutrients and water more readily than sandy soils. Soils with a high sand content are more easily leached of nutrients since they are lost to the subsoil layers with the passage of water through them. These nutrients which become leached into the soil are no longer available for plant use since they cannot be reached by the roots. These types of soils will be more likely to need nutrients added to grow plants successfully.

The best types of soils for nutrient retention have a balance between each of the mineral components i.e. sand, silt, and clay, and which also contain organic matter. In other words, loam soils. The reason that colloidal particles of clay and organic matter hold nutrients well is due to their small surface areas and negative charge, meaning they are able to bind to positively charged cation nutrients. These nutrients are bound to the soil particles whereas negatively charged nutrients are more readily available for plant uptake within the soil water solution.

4) Leaching

As we have seen, soils with a coarser sandy texture are more prone to leaching i.e. the water aided passage of soluble nutrients from the soil. Typically this involves the removal of nutrient anions since they are mostly freely available within the soil water solution and are not bound to soil colloids. Nevertheless, some anions such as phosphorous do sometimes bind to cations making them less prone to leaching.

With regard to nutrient cations, the strength of their positive charge varies and so they can be replaced by a more strongly charged cation. The cation exchange capacity is the amount of cations available for exchange in a soil at a particular time. As the cation exchange capacity increases, less cation nutirents will be lost due to leaching. Sandy soils which have a low cation exchange capacity lose more nutrients via leaching following irrigation or rainfall. As such, nutrient applications such be administered more frequently and so slow release fertilisers are appropriate.

Green manure crops that are dug back into the soil will produce nitrogen as they decompose. However, green manures that produce more nitrogen than the plants need will result in nitrogen leaching out of the root zone. The rate of release of nitrogen from green manure can be slowed by leaving the dead plant on the surface of the soil rather than digging it in.

5) Air and Water

Air and water are the routes through which all nutrients are obtained by the plant. Carbon and oxygen are obtained mostly from the air. Also, since they are required by all parts of the plant, the roots will rely heavily on the 'soil air' for their supply of oxygen and carbon. Thus, water logging is really more a form of suffocation. The soil becomes so saturated with water that the roots can no longer obtain the oxygen they need for respiration, and subsequently growth. Soils with high porosity are less prone to waterlogging and loss of nitrogen by denitrification, but they are also more freely draining and so are prone to increased loss of nutrients and salts by leaching. In any given soil, it is generally considered that there will be insufficient oxygen for root growth if the percentage of air falls below 10%. Furthermore, soil micro-organisms need oxygen in order to survive and so to recycle nitrogen, carbon and other elements for plant use.

A well structured soil has a mixture of large air holding pore spaces and small water holding pore spaces.

Aside from the air, other nutrients enter the plant dissolved in water. This is generally taken up by the roots from the soil or other growth medium. However, plants do also have a certain capacity for nutrient uptake from solutions sprayed onto the leaves. If soil moisture levels are low, not only does this mean that there are less water soluble nutrients available for plants, but also that recycling micro-organisms will diminish.

6) Temperature

As temperature increases, so too does microbial activity in the soil. In colder climates soil micro-organisms are less active and so the decomposition of organic matter and the mineralisation of nutrients occurs at a slower pace, meaning there are less nutrients available for plants. Conversely, soils in warmer climates have a lower organic matter content due to the increased microbial activity.

There are other factors which can affect plant nutrient uptake which are worthy of mention. These include: chemical pollution (oil and petrol spills from machinery; overspray of weedkillers, insecticides, fungicides; building materials), excess salinity which kills roots (due to rising water tables of land cleared of trees or excess fertiliser usage), denitrification or loss of nitrogen to the atmosphere (affected by the nature and quantity of organic matter present, degree of soil aeration, soil moisture content, pH and temperature), erosion (by wind or water).


As the name suggests, fertilisers are designed to make the soil more fertile by adding nutrients for plant growth. They may be organic (manure, compost etc) or inorganic (muriate of potash, superphosphate etc), and include soil conditioners such as lime and gypsum which make more nutrients available for plant uptake.

There are a tremendous variety of different fertilisers available, each with a different use. Using the wrong fertiliser or the right fertiliser at the wrong rate, can create problems in your garden rather than overcome them.

The variables include:
• Relative proportions of each nutrient
• Actual concentration of the nutrient (this is different in different types of fertilisers)
• Solubility
• Period of time over which the nutrient will be used
• What else is with the nutrient? (e.g. nitrogen applied as potassium nitrate will also supply potassium)
• Method of fertiliser application - to roots or foliage? Broadcast on the soil surface or buried in holes? In liquid or dry powder form? Watered in or not?
• Type of soil - will the fertiliser hold in the soil or be leached out?
• Type of plant and time of year - will the plant use the fertiliser quickly? Is it growing rapidly?

Types of Fertiliser

This type of fertiliser only contains one macronutrient e.g. muriate of potash, which only contains potassium. However, the term 'straight' is not strictly accurate since many straight fertilisers also contain other important nutrients. For instance, superphosphate contains phosphorous and sulphur.

These are manufactured through chemical processes and contain two or more macronutrients.
Each granule is of a uniform size and contains the same nutrients. They usually cost more than mixed fertilisers.

Mixed fertilisers contain two or more of the straight fertilisers with the aim of addressing particular nutrient requirements. Some fertiliser companies will also make up special mixes upon request.

These fertilisers are composed of granules or pellets which are easier to spread when applying. They are also a regular shape, free from dust.
Controlled Release
These are water soluble fertiliser particles with a protective exterior coat. This coat may either dissolve slowly to release the nutrients within, or it may expand and allow the fertiliser solution to pass through it. Various coatings are used but the polymer resin 'Nutricote' is widely used.

The rate of release is increased with higher temperatures which coincide with the fact that plants take up more nutrients and grow faster during the warmer months. Nutrient release is also independent of microbial activity and soil pH. Release rates can be adjusted according to the thickness of the nutricote layer. It is particularly useful for growing seeds, seedlings and plants in containers.

Slow Release
Slow release fertilisers are often organic e.g. blood and bone, compost, and manure. They are slow release because they have to be decomposed before the nutrients become available to plants. They generally contain fewer nutrients by weight than inorganic fertilisers. There are manures available in pellet form which serves the same purpose.

These are fritted trace elements and are created by heating sodium silicate with various salts. The resultant material is cooled in water and the split particles are ground down into a powder. Frits dissolve slowly to release nutrients. Various formulations are available which target specific trace element deficiencies, notably copper, magnesium, boron, and zinc. Librel and Sequestrine are examples. Trace elements should be applied with caution since there is a fine line between toxicity and deficiency.


Generally speaking, it is always better to apply too little than too much fertiliser since it is easier to add more than it is to remove excess nutrients.

The main ways of providing nutrients to plants are as follows:

A/ Mixing straight (organic or inorganic) fertilisers into potting soil before plants are potted up; and following with applications of liquid fertilisers at regular intervals
Soil which has such fertiliser incorporated into it must be used quickly (within a week or two of adding fertiliser). The fertiliser can leach out or change form if left for any period.

B/ Mixing fertilisers into the soil before potting, then adding additional fertiliser by topdressing on top of pots or ground at the base of the plants
Frequency of topdressing will depend upon the type of fertiliser being used and upon the characteristics of the potting mix or soil to leach out or retain nutrients applied.

C/ Mixing slow release fertilisers such as Osmocote ® into the soil right from the beginning, before plants are potted (or planted if in the open ground)
The slow release fertiliser might or might not be sufficient to feed the plant for its entire life in the nursery. Temperature and moisture can affect how quickly or slowly the fertiliser is depleted. Some fertilisers do not work at all in cooler climates during the winter months, and should normally be used only in sub tropical or tropical regions.

Any fertiliser mixed into a soil must be mixed thoroughly and evenly. Some nurseries do this themselves for instance by placing soil in a cement mixer and adding the fertiliser. Others have the soil supplier mix fertiliser for them. Pre-mixed soils are available from garden centres.

D/ Applying slow release fertiliser to base of the plant after planting or potting
This method is preferred by some because it allows flexibility to apply different types of fertilisers to different plants, and because it does not have the problem of having to ensure a thorough mixing of fertiliser in the soil/potting mix. It is important that the person doing this job does not overfeed or underfeed (a pinch is not good enough). Variations in the rate of feeding can cause variations in the growth habit and rate between plants.

E/ Using Liquid Fertilisers only, normally applied through either sprays or through the normal watering system
Liquid feeding can vary from daily to only once every 5 or 6 weeks. There are arguments for both ways. The danger is that overfeeding can burn plants and underfeeding will not achieve the growth required. The rate of feeding must be calculated carefully, and the application of liquid feeds must be very precise.

Moss/Algae/Liverworts can often grow on the surface of pots. This can be indicative of dampness but can also result from high levels of nutrients on the surface of the pots. If a layer of coarse sand is sprinkled on the top of the pot restricting light to the fertilised soil, this will deter their growth.

A White Cake on top if the soil indicates a build-up of salts from fertilisers applied. This can damage plant growth, and generally indicates over-feeding or insufficient leaching away of waste salts.

Choosing the Right Fertiliser
Using the right fertiliser helps to minimise wastage, reduce costs, and reduce the negative effects on the environment, while maximising plant growth.

• Timing is important so as not to waste fertiliser. In winter, some plants may be dormant so the fertiliser will not be taken up. Heavy feeding at the wrong time of year can also cause fruit trees to produce plenty of leaves at the expense of fruit.
• Commercial fertilisers are available for certain types of plants (e.g. citrus food, rose food) or as general preparations to suit most plants. However, some are produced from non-renewable resources.
• Quick-release or soluble fertilisers are very mobile which makes them easier for the plants to take up, but unfortunately most of the nutrients can be leached into streams or ground water, eventually ending up in rivers, bays, dams and estuaries, causing problems such as algal blooms.
• Using slow-release fertiliser can be a more efficient way of feeding plants, but again these may not be made from renewable materials.
• Home-made fertilisers can be prepared using compost, animal manures and mulch material. Some plants themselves are excellent sources of nutrients, including legumes (e.g. lucerne). Often weeds are able to absorb minor nutrients from the soil, so they can also be used if care is taken to ensure that the weeds have not set seed and will not re-establish.

Liquid manures should be diluted and applied frequently. There comes a point where strong organic manure can be as disastrous as chemical manures used injudiciously. Urine is excellent liquid manure if diluted to about 1:20 but if used at full strength, it will kill almost any plant.

Solubility of Fertilisers
The rate at which a plant is able to absorb a fertiliser depends on the solubility of that fertiliser (among other things).The solubility can be measured very simply by placing measured samples of different fertilisers into a jar full of water and shaking, then observing how readily the fertiliser has dissolved.

Application Rates
Inorganic fertilisers are often described by their relative percentages of nitrogen, phosphorous and potassium, otherwise known as the N:P:K ratio. Separate nutrients such as those found in 'straight' fertilisers can be applied where a known deficiency exists or where an abundance of a particular nutrient is known, but often mixed fertilisers are more appropriate in a home garden setting. NPK fertilisers ordinarily have calcium, sulphur and a range of trace elements included.

General purpose fertilisers are usually in the range of NPK 5:5:4. This ratio is also suitable for adding to pre-planting soil mixes and pre-sowing soil mixes. Pre-sowing seed fertiliser mixes for lawns are usually in the range 4:6:3, since the higher phosphorous level stimulates the growth of cells which are actively dividing e.g. roots and seedlings. Phosphorous also stimulates flower and fruit development and so applications with a high phosphorous level may be used for tomato plants and other fruits which have reached the budding stage.

Special mixes for acid loving plants contain higher nitrogen and potassium levels than phosphorous and include iron to maintain soil acidity. Typical NPK ratios would be 6:3:5 or 10:4:10.

Fertilisers to stimulate growth of leafy vegetables and lawns have higher nitrogen ratios e.g. 13:2:4 due to the strong association between nitrogen and leaf growth.

Other slow release mixes which are based on organic components such as blood and bone are designed to stimulate growth in shrubs with shallow fibrous rooting systems where there is a risk of root damage from fast acting concentrated fertilisers e.g. rhododendrons, camellias, azaleas.

Other Factors Affecting Fertiliser Application
Different plants will use fertilisers at different rates. Slow growing plants should be fed at lower rates to quicker growing plants.

Fertiliser will wash through more sandy (better draining) soils much faster, and should be applied more often and in smaller quantities.

The pH (acidity or alkalinity) of the soil affects the availability of different nutrients in different soils or mixes. If the pH is very acid (e.g. pH 4) certain nutrients such as iron are able to be absorbed easily by plants, but others such as nitrogen are not able to be taken up as easily as they are at a higher pH. Every nutrient has its own ideal pH. Different plants require different amounts of different nutrients, and this fact makes it preferable to have the soil pH at different levels to achieve the optimum nutrient uptake by different types of plants. Some species grow better at pH 5; others fare better at pH 7, but most prefer a pH of around 5.5 to 6.5.

Application of Liquid Fertilisers
The simplest device to use is a standard chemical sprayer. Because of the quantity of plants being fed, the chemical is normally applied in a concentrated solution and immediately watered with normal irrigation to wash it off the leaves and into the pots (preventing burning of the leaves). A better method involves automatically mixing the fertiliser into the irrigation system using a fertiliser injection device such as a Geewa. These units are precise, and allow the fertiliser to be applied at very low concentrations, regularly, quickly and with very low labour costs.

Salinity Problems with Fertilisers
Telltale signs of salt affected soils include dieback of plants and a white crusty layer of salt which is deposited on the soil surface as water is evaporated away. Salinity can also be a problem in gardens that have been excessively fertilised using artificial fertilisers as well as in coastal areas.

Fast release fertiliser has a high chemical salt content and rapidly builds up the salt in the soil. This can be leached out with lots of water (or heavy rain) but still can cause problems if too much reaches the roots of sensitive plants and remains in contact with these roots.

How to Overcome Salt Problems in the Home Garden
Leaching with water can be effective in areas where high groundwater tables are not a problem.
Reduce applications of artificial fertilisers.
Use different fertiliser types, for example organic types such as compost and manures.
Use deep rooted plant species that will help lower the local water table.
Often the only way to overcome this problem in a home garden with a severe salinity problem is to grow salt tolerant plants.

Plants Sensitive to Saline Conditions
Aster, Apple, Azalea, Banana, Bauhinia, Camellia, Citrus, Dahlia, Fuchsia, Gardenia, Geranium, Gladiolus, Grape, Magnolia, Passion fruit, Podocarpus, Poinsettia, Primula, Prunus, Rose, Violet, Azalea, Magnolia ,Parsnips ,Green Beans, Cucumber, Pea, Carrot, Sweet Corn, Persimmon, Loquat, Cherry, Plum

Plants Tolerant of Some Degree of Salinity
Acacia sophorae, Bamboo, Bougainvillea, Carnation, Casuarina cristata, Casuarina glauca, Casuarina stricta, Coprosma, Chrysanthemum, Eucalyptus botryoides, Eucalyptus camaldulensis, Eucalyptus sargentii, Hibiscus, Melaleuca pubescens, Metrosideros, Myoporum, Oleander, Phoenix canariensis, Robinea pseudoacacia, Tamarisk.

Plants Very Tolerant to Salinity
Canary Palm, Paspalum vaginatum, Date palm,

Loss of Soil Fertility
Sustainable soil fertility implies that soil nutrients will be available in the same quantity in the long term. For this to happen, nutrients that are removed from the soil (in the form of plant crops, leached nutrients, cleared vegetation etc) need to be replaced. In a sustainable system, the gardener strives to work with the natural nutrient cycle to ensure that nutrients do not build up or get lost. The main problem is a loss of soil nutrients. There are a number of ways to reduce the loss of nutrients from the soil, including applying manure produced from the soil back to it and minimising losses due to erosion, de-nitrification and leaching.

Minimising De-nitrification
Soil de-nitrification (i.e. loss of nitrogen to the atmosphere) is affected by the nature and quantity of organic matter present, degree of soil aeration, soil moisture content, pH and temperature. Management practices can reduce nitrogen loss caused by these factors. For example, whilst you may have little control over rainfall, you can manipulate soil moisture content through irrigation and drainage practices. Saturated soils can produce the anaerobic environment required for de-nitrification, so irrigation practices can be timed to avoid water-logging.

Adding large amounts of organic matter to soils can result in high rates of microbial expansion, which in turn leads to an anaerobic environment which denitrifies quickly. This presents a dilemma, as organic matter is a highly beneficial ingredient in sustainable soil systems. In the long term, it increases aeration which improves soil structure, so making de-nitrification less likely.

Organic nutrients should be applied as close as possible to the time when they will be required by the crop. If it is essential to apply the nitrogen ahead of time, planting a cover crop that will accumulate the nitrogen may be necessary. The nitrogen can be stored and released for future use by decomposition.

Nitrogen should be applied in an even concentration over the entire area. Localised build-ups will accelerate de-nitrification.

Soil Sodicity
Saline soils typically have a build-up of sodium chloride. In sodic soils, much of the chlorine has been washed away, leaving behind sodium ions (these are sodium atoms with a positive charge) which are attached to tiny clay particles in the soil. This makes the clay particles less able to stick together when wet – leading to unstable soils which may erode or become impermeable to both water and roots.

Affected soils erode easily, and in arid regions, sodic soils are susceptible to dust storms. In sloping areas, water easily removes the topsoil. Where the subsoil is sodic, water flowing below ground level can form tunnels which later collapse into gullies. The biggest problems occur when the top 5 cm of soil are sodic. However, when lower soil layers are affected it can also be a problem, as drainage is affected.

Sodic soils are usually treated with calcium-containing substances such as gypsum. Other ameliorants such as sulphur, aluminium and iron sulphates or iron pyrite can be effective. Gypsum is the most cost effective treatment that is readily available for treating large areas. In some cases, soils need to be deep ripped to allow penetration

Soil Acidification
This is a problem becoming increasingly common in cultivated soils. Soil acidification is the increase in the ratio of hydrogen ions in comparison to 'basic' ions within the soil. This ratio is expressed as pH, on a scale of 0 14 with 7 being neutral, below 7 acid, and above 7 alkaline. The pH of a soil can have major effects on plant growth, as various nutrients become unavailable for plant use at different pH levels. Most plants prefer a slightly acid soil, however an increase in soil acidity to the levels being found in many areas of cultivated land renders that land unsuitable for many crops, or requires extensive amelioration works to be undertaken.

Causes of Soil Acidification
Acid soils can be naturally occurring, however, a number of agricultural practices have expanded the areas of such soils. The main causal factor is the growth of plants that use large amounts of basic ions (e.g. legumes), particularly when fertilisers that leave acidic residues (such as superphosphate or sulphate of ammonia) are used. Soil acidity is generally controlled by the addition of lime to the soil, by careful selection of fertiliser types and sometimes by changing crop types.


Refer to, and read any reference material you have access to that relates to the aim of this lesson.

This may include any of the following:
• Books in your own possession, or which you find in a library
• Periodicals you have access to (i.e. magazines, journals or newspapers)
• Websites

Spend no more than 2 hours doing this.


1. Look carefully around your own garden, your neighbours gardens and local parks, etc. for evidence of nutrient deficiency problems such as those mentioned in this lesson.

• What do you think has caused the problem?
• Has anything been done to overcome the problem?
• How would you go about rectifying the problem?

2. Contact nurseries, garden centres, the Department of Agriculture or other appropriate government departments, or conduct internet research to find out as much as you can about different types of fertiliser mixes (straight, compound, slow release, controlled release, and frits). Make notes.

3. Obtain samples of 3 different fertilisers.

Test each one in turn by placing one tablespoon full of fertiliser into a jar along with 1 cup full of water, then shaking ten times.

After shaking, observe how much residue, if any is left from the fertiliser being tested.

Grade the three different fertilisers according to most soluble through to least soluble.



1. Write a report on your findings from Set Task 1 (half a page).

2. Describe symptoms of the following nutrient deficiencies:
• Nitrogen
• Phosphorous
• Potassium
• Magnesium
• Calcium
• Iron
• Magnesium

Write a paragraph for each, or tabulate your answer if you prefer.

3. Describe how each of the following can influence the availability of nutrients in soil and growing media:
• pH
• Texture
• Soil Organisms
• Temperature
• Oxygen
• Water Availability
• Leaching

4. Write a paragraph describing each of the following fertiliser mixes which you researched in Set Task 2:
• Straight
• Compound
• Slow release
• Controlled release
• Frits

5. How can different fertilisers be chosen to optimise plant growth? How can application rates influence plant growth? Give examples. Write up to one page.

The ACS tutors and subject matter experts have many years experience within the horticulture industry.

John L. Mason Dip.Hort.Sc., Sup'n Cert., FIOH, FPLA, MAIH, MACHPER, MASA
Mr Mason has worked in horticulture since 1971 when he graduated from Australia's leading Horticultural College -Burnley. He has worked extensively around the world, in both Victoria and Queensland (Australia) and the UK. Former nurseryman, landscaper, parks director and horticultural consultant. Editor of 5 gardening magazines, author of more than 70 books, including 'Trees and Shrubs for Small Gardens' and 'Orchids: A beginners Guide'. John
started teaching in the early 1970's.
Dr Lynette Morgan B.Hort.Tech(Hons), PhD in hydroponic greenhouse production
Partner in SUNTEC International Hydroponic Consultants
, Lynette is involved in many aspects of production horticulture production, including remote and on site consultancy services for new and existing commercial greenhouse growers worldwide as well as research trials and product development for manufacturers of hydroponic products. Lynette is also the author of 6 hydroponic technical books
Bob James QDAH. B. Applied Sc(Hort Tech),Grad Dip. Mgt, M;Sc (Enviro Sc.), PDC.
Bob has over 50 years experience in Government and Private Horticulture and Environmental Management Consulting.
His work is diverse across most branches of horticulture including nurseries, landscaping, horticultural education, environmental assessment, land rehabilitation; and more.

Adriana Fraser Cert.Hort., Cert.Child Care, Adv.Cert.App.Mgt., Adv.Dip.Hort.
20 years of experience in horticulture, business and journalism.
Adriana has written regularly for a range of publications (including Australia's national Grass Roots Magazine) since the early 1980's.She operated a commercial display herb garden in her previous home, hosting visits regularly for all types of groups. She is developing a similar venture at her new property and continues to be actively involved in writing, tourism and practical gardening; in addition to her work for ACS.
Maggi Brown
Maggi is regarded as an expert in Organic Growing throughout the UK, having worked for two decades as Education Officer at the world renowned Henry Doubleday Research Association. She has been active in education, environmental management and horticulture across the UK for more them three decades. She has exhibited at Chelsea Flower show and worked widely as a consultant for decades.
Gavin Cole B.Sc., Cert.Garden Design, MACA
Gavin has three decades of industry experience in Landscaping, Publishing and both the UK and Australia, across landscaping and the amenity plant sector. He was operations manager for a highly reputable British Landscape firm (The Chelsea Gardener) before starting up his own firm. He spent the best part of three years working in our Gold Coast office

Diana Cole B.A. (Hons), Higher Dip. (Garden Design), RHS Advanced Cert. Horticulture, Cert Admin.Mgt., Dip. Inst. Personnel Management
In addition to her RHS horticulture, garden design, City & Guild construction, NPTC pesticide/legislation and business/management qualifications, Diana has a variety of skills drawn from setting up Arbella Gardens, a landscape gardening business. She also has administrative, management and training delivery experience drawn from her employment in other organisations such as the NHS and other educational institutions such as schools & universities. She has augmented her training expertise having gained the Preparing to Teach in the Life Long Learning Sector qualification. She also has experience gained through working as a volunteer in a number of different roles including amenity style gardening in parks and practical conservation work.

Rosemary Davies Dip Hort Sc. Originally from Melbourne, Rosemary trained in Horticultural Applied Science at Burnley, a campus of Melbourne University. Initially she worked with Agriculture Victoria as an extension officer, taught horticulture students, worked on radio with ABC radio (clocking up over 24 years as a presenter of garden talkback programs, initially the only woman presenter on gardening in Victoria) and she simultaneously developed a career as a writer. She then studied Education and Training, teaching TAFE apprentices and developing curriculum for TAFE, before taking up an offer as a full time columnist with the Herald and Weekly Times and its magazine department after a number of years as columnist with the Age. She has worked for a number of companies in writing and publications, PR community education and management and has led several tours to Europe. In 1999 Rosemary was BPW Bendigo Business Woman of the Year and is one of the founders and the Patron, of the Friends of the Bendigo Botanic gardens. She has completed her 6th book this year and is working on concepts for several others.


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