The Gardener's Almanac

Fertiliser

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!

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

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

In recent years there are more and more plant foods & composts that are becoming ‘plant specific’ do not let this dissuade you.

All it means is; that many plants require different proportions of NPK and these products are produced to cater for this need.

To assist in choosing the correct one for the situation, it is useful if one can understand the meaning of manufactures instructions on the packaging.

The quantities of fertilisers contained within a manufactured product, are denoted within the N.P.K. formula marked on the packaging.

Here are some of the things you would expect to see;

The name of the product.

the major nutrient contents, e.g. nitrogen (N), phosphorus (P) and potassium (K); (see list below)

NPK fertiliser 7.5 : 3.6 : 5.2

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 what these details mean 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%

Further details 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.

Note; it must be noted that these guidelines 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 all packaging.

Now think of the growing habits of plants!

First to come (normally) is the leaves, and these generally require nitrogen (N)

(N) The symbol for nitrogen, promotes plant growth.

Note; too much nitrogen can produce soft lush growth and large leaves, which is not always desirable.

Next is (P) the symbol for Phosphates this promotes a good healthy root systems.

Next is (K) the symbol for Potash, this promotes flowering, fruiting, and ripening.

As you can see; basically NPK is in the growing sequence.

When purchasing a high nitrogen fertilizer the (N) figure will be the biggest number, e.g. 25: 15: 15,

Similarly high potash may read 15: 15: 30

A balanced feed may read; 1:1:1 or 20:20:20 this indicates that there are equal proportions of Nitrogen/Phosphate/Potash in the mix

And sometimes a low nitrogen feed is called for, this might read 12.5: 25; 25

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

Other factors that you may come across;

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 or Magnesium 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.

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.

Most fertilisers credited with exceptional results are generally high potash feeds, meaning any cheaper high potash feed, may do equally as well.

Specific Plant Foods;

Organic manures & fertilizers;

Well rotted farmyard manure; is an excellent bulky soil conditioner.

Dried poultry manure ; is high in nitrogen and potash.

Garden compost and kitchen waste; is generally high in various nutrients.

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

Bone meal ; is a slow-release fertilizer, high in phosphorus.

Hoof and horn meal; is a slow-release nitrogen feed.

Dried blood; is a fast-acting nitrogen feed for summer use

Fish, blood and bone; is a balanced general feed

Seaweed; 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% (7lb/ ton), phosphoric acid 0.1% (2lb/ ton) potash 1 % (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; from 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)

Note; 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.

Lime;

Ground chalk & 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.

Magnesium sulphate (Epsom salts); corrects magnesium deficiency.

Superphosphate; is concentrated phosphorus.

Sulphate of potash; is a top-grade source of potash.

Sulphate of ammonia; is a very fast-acting nitrogen feed.

Potassium nitrate; contains potash and nitrogen, and is ideal for legumes.

Compound & 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 & 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.