Plant nutrition both indoors and out, depends largely on the amount of nutrients available in the soil or compost they are being grown in.

Outdoors nutrients may leech out of the soil by the actions of the weather, whereas indoors, this will be caused by the watering of the plant and the plant using up all the available nutrients in the pot.

Either way the gardener will need to supplement these lost nutrients in some way to ensure a degree of success.

For example; all plants need the following nutrients;

Nitrogen (N) to promote stem and leaf growth.

Phosphorus (P) supplied as phosphoric acid for root growth.

Potash (K) for fruitfulness and ripening.

Trace elements such as Iron (fe), Magnesium,(mg) Manganese,(mn)and Boron.(B)

Listed below are some techniques and information to ensure that these conditions are met.

Soil nutrition:

Most garden soils usually contain sufficient amounts of the major nutrients e.g. phosphorus (P) and potassium (K) , and trace elements such as iron (Fe) and magnesium (Mg) , plus small amounts of nitrogen (N).

On occasions you might think that your plants are deficient of fertiliser/s, when in fact your plants are actually receiving insufficient moisture, and / or the soil structure is poor, which in turn may be preventing the plant roots finding the nutrient they need.

Or there maybe an imbalance of chemicals where one type prevents another type being released, for example, lack of potash may be preventing the plant/s making proper use of the nitrogen available in the soil.

Then there are other potential causes e.g. the presence of pests,disease, and / or an excess in alkalinity or acidity in the soil.(pH).

In many cases, soil problems can be cured by the generous use of bulky organic matter, either dug in or used as mulch.

This will improve the structure of the soil by releasing nitrogen and other plant nutrients including trace elements, into the soil, and also help to prevent water-logging in winter and drying out summer.

Most animal manures contain all necessary foods but not necessarily in the amounts plants require, meaning that feeding will need supplementing.

If after soil improvement plants still fail to thrive, then have a soil test done.

If it is a deficiency problem this will highlight what is lacking, or indeed what is in excess as the case may be.

Correcting deficiencies:

Nitrogen (N) deficiency:

Nitrogen is required to promote foliage, and general growth.

The signs of a deficiency are pale green-yellow leaves, sometimes with pink tints, and spindly plants.

Nitrogen compounds are highly soluble in water, and can be readily washed out of the soil by winter rains.

As mentioned above, adding organic material will help to maintain levels of nitrogen as it decays.

There are also a number of organic / inorganic products on the market that will remedy this problem, products such as Sulphate of Ammonia, Dried Blood, and Poultry manure pellets.

*Always add any of these at the prescribed dosage as stated on the packaging.

Phosphorus (P) deficiency:

This element is used in rapidly growing parts of plants such as the roots.

Phosphorus deficiency shows up as dull, yellowed foliage and slow growth.

Phosphorus tends to accumulate in the soil of most gardens, particularly if a regular feeding regime has been performed meaning a deficiency is uncommon.

However it may occur in areas with high-rainfall, and where the soil is heavy clay.

Superphosphate and/or Bonemeal should make right any shortfalls when added at the prescribed dosage as stated on the packaging.

Potassium (K) deficiency:

Plants need potassium to control water uptake and photosynthesis.

Again, as with nitrogen, this can readily be washed out of the soil, particularly light, sandy or chalky soils.

The symptoms can look similar to a nitrogen deficiency i.e. leaves may turn blue, yellow or purple with brown blotches or dis­coloration within, or at the edges of leaves.

Other symptoms are lack of growth, poor flowering and or fruiting.

There are a number of high-potassium fertilizers available, e.g. Sulphate of Potash that will cure the problem.

Add at the prescribed dosage as stated on the packaging.

Magnesium deficiency:

Magnesium is an essential nutrient that is used by all green plants to make chlorophyll, which is vital for photosynthesis.

The first sign of deficiency appears on the lower half of the plant/s, and is recognized when a yellow discoloration is seen between the leaf veins, plus premature autumnal leaf tints and dying leaves.

Eventually the problem will move up the plant/s if left untreated.

Magnesium deficiency is common in acid, sandy soils, with low organic matter levels, or where heavy applications of potassium rich fertilisers have been made.

In spring top-dress the bed/s with of Epsom salts (Magnesium Sulphate) applied at a rate of 30g (1oz) per sq m.

Apply the top dressing to a moist bed and was off any that comes in contact with the plants.

If symptoms appear during the growing season, apply a foliar spray* containing Epsom salts (Magnesium Sulphate) at 20g (½oz) per litre of water.

*Adding a few drops of washing-up liquid to this mix will help the solution stick to leaves.

Don’t spray in bright sunlight, to do can result in scorched leaves.

Repeat the treatment three times at fortnightly intervals.

Trace-element deficiency:

As mentioned above it is best to seek expert advice before adding trace elements.

Manganese (Mg) and Iron (Fe) deficiencies are relatively common, and appear as a yellowing of leaves (known as chlorosis) and browning on the leaf edges.

This can occur when acid-loving plants are grown in alkaline soils, when excess lime has been inadvertently applied or hard water is used for irrigation.

It is possible to acidify soil with Sulphur or Chelated iron, or to apply foliar sprays of Manganese Sulphate, but choosing plants that suit the soil is the better long-term solution.

Potting Composts:

When a plant has been potted for 5 to 6 weeks, most compost will have exhausted their supply of nutrients, therefore supplementary feeding is necessary.

This can be done by adding one of the many liquid / powder plant fertilisers available from garden centres.

Selecting the right one might prove to be a bit daunting to some people, but do not despair!

Various Liquid Feeds

As a result of government legislation, packaging is required by law to include a number of details such as its basic uses and contents.

These details should allow the purchaser to compare different products and find a fertiliser to meet their specific needs.

For example:

A balanced fertiliser is one that supplies the essential ingredients in approximately the right proportions for the crop in question.

Most chemicals usually supply only one of the ingredients required, though a few such as Nitrate of Potash, and Phosphate of Potash supply two.

In order to obtain a well balanced chemical fertilizer several chemicals must be mixed in correct proportions.

By law these proportions must be quoted on the packaging.

The analysis is always given in the following order Nitrogen (N) Phosphorous (P) Potash (K)

For example; a fertilizer described as 15: 15: 30 would contain 15% Nitrogen, 15% Phosphoric Acid and 30% Potash.

Fertiliser types:

Specific fertilisers supply only one major plant food, e.g high Nitrogen (N) or high Potash(K)

Compound fertilisers supply at least two major plant foods, e.g low nitrogen (N) high potash (K)

Balanced fertilisers supply all three in the same proportions.

Packaging Information:

To assist in choosing the correct product for a given situation, it is useful if one understands the meaning of the data on the packaging, here are some of the things you would expect to see on a typical package;

The name of the product.

The major nutrient contents i.e. Nitrogen (N), Phosphorus (P) and Potassium (K)

NPK fertiliser ratio 7.5 : 3.6 : 5.2 which equates as;

Total Nitrogen (N) 7.5%

Phosphorus pentoxide (P2O5) soluble in neutral ammonium citrate and in water 3.6% (1.6 %)

Potassium Oxide (K2O) soluble in water 5.2% (4.3%)

Magnesium oxide (MgO) 4.2% (2.52%)

Trace elements:

Boron (B) 0.03%

Copper (Cu) 0.06%

Iron (Fe) 0.37%

Manganese (Mn) 0.16%

Molybdenym (Mo) 0.04%

Zinc (Zn) 0.13%

A further explanation of these details is:

The mixture contains; 7.5% Nitrogen (N), 3.6% Phosphorus (P), 5.2% Potassium (K)

Total Nitrogen (N) 7.5%

Phosphorus (P) content as oxide 3.6%, and more usefully as phosphorus (1.6%)

Potassium (K) content as oxide, 7.0% and as more useful potassium (5.8%)

Magnesium oxide (MgO) content as oxide, 4.2% and as more useful magnesium (2.52%)

Various trace elements approx 0.8%

Supplementary Information:

Additional information such as the name and address of the manufacturer, the guaranteed weight of the product, and an EC product declaration, if the product is EC approved should also be displayed on the packaging.

Most manufacturers add comprehensive information to help gardeners get the best from their products.

This information will have probably come as a result of tests and trials they have carried out.

However, it must be noted that these guidelines will not / cannot cover every possibility, and gardeners may have to use trial and error methods to achieve the results best suited to them.

A rule of thumb that might help in determining your needs is as follows:

The letters NPK are always shown in the same order on the packaging, armed with this knowledge one should then consider the growing habits of plants e.g.

The first thing to appear (normally) is the leaves, to promote a healthy leaf system and encourage plant growth, add Nitrogen (N).

Secondly plants require a good healthy root system, this task can be achieved with the addition of phosphates (P).

Finally, flowering, fruiting, and ripening can be improved with the addition of potash (K)

As you can see NPK is basically in the same order as the growing sequence.

What to look for prior to purchase:

When purchasing a high nitrogen fertilizer (N) ensure that the first number is the highest e.g. 25: 15: 15.

Similarly high potash (K) may read 15: 15: 30

A balanced feed may read; 1:1:1, 7:7:7, or 20:20:20

This indicates that there are equal proportions of Nitrogen/Phosphate/Potash in the mix.

A low nitrogen feed might read 12.5: 25; 25 where the characteristic is the lowest number.

Some manufactures may use a different numbering system e.g. lower numbers but the principle is the same.

Other factors:

Trace elements:

It would suffice to say, that as these are generally in such minute quantities they should cause no concern, and in most cases the matter has been addressed by the manufacturer.

Plants are sometimes subject to mineral deficiencies such as Boron (B) or Magnesium (Mg) but in these cases it is best to buy specific products, i.e. products that have been produced for easy use by the amateur grower.

Trace Elements Powder

Foliar feeding:

Most of the liquid fertilizers are suitable as foliar feeds.

Foliar feeding can be quite beneficial to seedlings and cuttings that have not yet achieved their full root system.

Some expensive fertilisers credited with exceptional results are generally high in either N or K, meaning any cheaper high N or K feed, may do equally as well.

Compare the NPK value of both products on the packaging and purchase accordingly.

Specific Plant Foods:


Well rotted farmyard manure:

Is an excellent bulky soil conditioner,and contains variable amounts of fertiliser.

On average these amounts could be; ½ to 1% N (5-10kg/tonne) - ¼ to ½% P (3-5Kg/tonne) and ½ to 1% K (5-10kg/tonne)

Apply at approx 5kg per sq m.

Dried poultry manure:

Is high in nitrogen and phosphate.

On average these amounts could be; When moist; 1½% N - 1½% P - ½ to ¾% K and 4% N - 3% P - 1½% when dried.

Apply at 225-550 gms (8-12oz) per sq m.

Garden compost and kitchen waste:

Contains variable amounts of fertiliser.

Apply at approx 5kg per sq m.

Brand name composts for general use are generally purchased for selective applications.

Bone meal:

Is a slow-release fertiliser, high in phosphorus.

Up to 5% N - up to 25% P

Apply at 115gms (4oz) per sq m.

Hoof and horn meal:

Is a slow-release nitrogen feed.

Up to 15% N - up to 3% P

Apply at 60gms (2oz) per sq m.

Dried blood:

Is a fast-acting nitrogen feed for summer use.

Up to 15% N - up to 3% P

Apply at 60gms (2oz) per sq m in powder form or 30gms (1oz) per 5litres (1gall) in liquid form.

Fish, blood and bone:

Is a balanced general feed.

Up to 10% N - up to 10% P - 10% K

Apply at 115gms (4oz) per sq m.


Is a valuable substitute for manure,the bladder and drift seaweeds are the best kinds

It is rich in potash and almost lacking in phosphates.

Analysis varies according to variety.

An average for fresh seaweed is; nitrogen 0.3% N (7lb/ ton), phosphoric acid 0.1% P (2lb/ ton) potash 1 % K(20lb/ton).

It can be used wet (as collected) or dried.

Dig in at a rate of 6kg (15lbs) per sq metre wet, or 2kg (5lb) per sq metre dried.

Wood ash:

Ash f rom a bonfire or wood burning stove is a useful soil improver.

The type of wood burned can have different results e.g.

Ash from untreated wood has a slight liming action and can be used to raise soil pH.

Ash produced from young sappy growth contains potassium and traces of other nutrients.

On the other hand older mature wood tends to contain lower concentrations of nutrients.

The actual nutrient content of ash varies so precise application is difficult, listed below are a few suggestions;

Where ash contains large particles, it is probably best to dig this in to improve the structure of the soil.

Adding finer ash to the compost heap / bin in thin layers will allow it to blend with other materials.

Alternatively, rake the fine ash into the surface of the soil if you are sure of its content. (see note below)

In the event that some unknown product with toxic properties may have been burned along with the wood, it is probably safer to allow ash to weather in a heap for a few weeks, before spreading it around growing plants.

Coal ash:

Is best avoided because it has a negligible nutrient content and its fine particle size means it is of little benefit to soil structure, plus, it may contain toxic by-products.


Ground chalk and ground limestone are excellent for correcting acidity.

Hydrated lime is fast-acting but is easily washed out of the soil.

Magnesium limestone (Dolomite) is source of magnesium and lime.

Inorganic fertilizers:

Nitrate of soda

Is nitrogen-rich.

Up to 15% N

Apply at 30gms (1oz) per sq m in powder form or 15gms (½ oz) per 5litres (1gall) in liquid form.

Magnesium sulphate:

(Epsom salts) corrects magnesium deficiency.

Up to 10% MgO

Apply at 30gms (1oz) per sq m in powder form or 30gms (1 oz) per 5litres (1gall) in liquid form.


Is concentrated phosphorus.

Up to 20% P

Apply at 85gms (3oz) per sq m.

Sulphate of potash:

Is a top-grade source of potash.

Up to 50% K

Apply at 30gms (1oz) per sq m.

Sulphate of ammonia:

Is a very fast-acting nitrogen feed.

Up to 20% N

Apply at 30gms (1oz) per sq m.

Potassium nitrate:

Contains potash and nitrogen, and is ideal for legumes.

Up to 15% N - 10% K

Apply at 30gms (1oz) per sq m.

Compound and brand name concentrated granular and liquids fertilizers are for specific or general use.

The nutrient content and application rate of fertilizers is normally declared on the packaging.

Does and Don’ts:

Never feed if soil temperatures are very low.(10C)

Never feed if soil temperatures are too high.(25C)

Never foliar feed if plant is in flower, (unless you protect the flower)

Never foliar feed in full sunlight.

Never exceed manufactures dosage.

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