A Guide to Fertilisers


Gardeners take more from their soil than nature ever intended, so if your plot is to be successful, you must put something back.

There are basically two ways of doing this, first, the ever more popular Organic method which involves a LOT of organic matter and second, the Inorganic method, which is using mainly man made fertilisers.

It's important to understand the difference between manures and fertilisers.

MANURES are bulky materials such as garden compost or animal wastes, which usually contain straw type bedding. Manures do contain some nutrients, but, unless used in very large quantities not enough. They do play a very important part in soil fertility though and should be looked upon as soil conditioners. They are classed as being organic and are slow acting. This means that they provide plants with the nutrients (mostly nitrogen) over a long period of time.

FERTILISERS contain plant foods in concentrated form. These are classed as being organic or inorganic. Organic fertilisers are often of the slow release, whereas inorganic are usually faster acting. They come either as a 'compound' fertiliser which contains a mix of the three major nutrients in varying proportions, or as a 'straight' fertiliser which is only a major nutrient on it's own.

Organic fertilisers are safer to use than inorganic ones and they do not harm the soils natural organisms, in fact they positively help them. They can be spread freely around plants, as there is not as much need to precisely measure them, although it is best not to overdo it. They do depend on the micro-organisms in the soil to break them down though and these organisms are not active in cold, very acidic or waterlogged soils.

Inorganic or artificial fertilisers are minerals extracted from the earth or completely manufactured. Although plants cannot tell the difference in the minerals, it is known that they do damage to soil organisms and they repress the natural nitrogen making activities of bacteria. They need to be measured and applied fairly accurately to avoid damage.

Care should be taken when handling ANY fertiliser and the instructions on the packets should be followed strictly. Using too much can upset the balance of the soil and damage plants by burning them, besides which, it is an unnecessary waste of money.


Both natural and man-made fertilisers are measured by the three MAJOR Nutrients that are in them. These are: -

Nitrogen (N), - assists plant in leaf and stem growth.

Phosphorus (P). (More commonly referred to as PHOSPHATE) - assists young plants and root crops to develop good root systems.

Potassium (K) (More commonly referred to as POTASH)- assists plants to produce flowers and fruit.

Fertilisers also contain SECONDARY NUTRIENTS, which are: -

Calcium (CA) - most fruit, flowers, and vegetables need some calcium.

Magnesium (Mg) - Roses and Tomatoes need these most.

Sulphur (S) - most plants.

Fertilisers also contain trace elements, which various plants need. These trace elements are usually in such minute quantities in everyday fertilisers that they are of little benefit. If soil is kept in good condition these Trace elements are usually present in sufficient quantity for most needs. If a plant needs more of a specific trace element, it is usually applied as a specialist fertiliser. For reference the trace elements are: -

Iron (Fe) - usually needed by acid loving plants like Azaleas and Rhododendrons.

Manganese (Mn) - as above.

Molybdenum (Mo) - needed by Brassicas.

Boron (B) - needed by root vegetables.

Zinc (Zn) - fruit and vegetables.

Copper (Cu) - Fruit and vegetables.

The following tables show organic and inorganic fertilisers and their respective uses, speed at which they work and the rate of application.



%N %P %K Speed Application Rate Notes
Blood, Fish & Bone 3.5 8.0 0.5 Medium 1 - 2 oz per Sq. Yd. A popular fertiliser that contains all three major nutrients
Chicken Manure Concentrate 6.0 5.0 3.0 2 - 8 oz per Sq. Yd. Popular fertiliser used as base or top dressing.
Hoof and Horn 14.0 2.0 0 Slow - Medium 2 - 4oz per Sq. Yd. Apply 2 weeks before planting.
Bone Meal 4.0 20.0 0 Slow 2 - 4oz per Sq. Yd. Apply in Autumn or Spring.

Check on pkt. That it has been sterilised for safety.

Soot 3.0 - 6.0 0 0 Quick 4oz per Sq. Yd. Allow to weather before use as a top or base dressing.
Dried Blood 12.0 Trace Trace Medium 1-2oz per Sq. Yd. Apply in late Spring / Summer.
Fish Meal 6.0 - 10.0 6.0-12.0 1.0 Slow - medium 2-4oz per Sq. Yd. Apply as a Winter /Spring base dressing.
Wood Ash 0 0 5.0-10.0 Quick 4-8oz per Sq. Yd. Do not use on chalky soils.


All can either be dug into the soil or used as a surface mulch.

Humus maker %N



Speed Application Rate Notes
Farmyard Manure .5 .25 .5 Slow 1 bucket per Sq. Yd. Needs to be well rotted before use.
Garden Compost 1.5 2.0 .5 Slow 1 bucket per Sq. Yd. For more info on Compost see separate leaflet.
Leafmould .5 .25 .25 Slow 1 bucket per Sq. Yd. Takes a long time to rot down but well worth the wait.
Bark .25 0 0 Very Slow 1" layer Usually used as a mulch. See separate leaflet about Mulching.
Green Manures 2.0 .25 .75 Slow - medium Dig in during Autumn / Winter. See separate leaflet on Green Manures.



%N %P %K Speed of Action Application Rate Notes
Super - phosphate 0 18.0 0 Quick 2-4oz per Sq. Yd. Basic source of phosphate. Use as a base dressing.
Triple Super Phosphate 0 47.0 0 Quick 1-2oz per Sq. Yd. Use as a base dressing.
Sulphate of Potash 0 0 48 Quick .5- 1.0oz per Sq. Yd. Basic source of potash. Use as a base dressing.
Sulphate of Ammonia 21.0 0 0 Quick .5-1.0oz pr Sq. Yd. Basic source of nitrogen. Tends to make soil more acidic. Favourite for greening up lawns.
Potash Nitrate 15.0 0 10.0 Quick 1-2oz per Sq. Yd. Apply sparingly in Spring / Early Summer as a general top dressing.
Growmore 7.0 7.0 7.0 Quick 1-4oz per Sq. Yd. Very popular general fertiliser. Use in Spring as a dressing.
Nitrate of Potash 16.0 0 0 Quick 1-2oz per Sq. Yd. Apply in Spring. Much used in liquid form.
Nitrate of Soda 16.0 0 0 Quick .5-1.0 per Sq. Yd. Very quick acting but scorches leaves on contact. Makes clay soils stickier.
Nitro Chalk 16.0 0 0 Quick 1-2oz per Sq. Yd. Contains lime. Useful for reducing acidity of soils.
Phostrogen 10.0 10.0 27.0 Quick 1tsp per 2 gal water General purpose feed. Apply during growing season. Diluted can be used as a foliar feed.
Rock Phosphate 0 10.0 0 Slow 4oz per Sq. Yd. Apply in Autumn / Winter. Good for acid soils.

Liquid Fertilisers

Liquid fertilisers have the advantage over solids, that they are instantly available to plants. They also have the disadvantage that they do not remain in the soil for very long.

They have to be used on a regular basis, either to supply nutrients to high demand plants such as Tomatoes or to quickly correct deficiencies in the soil.

They come in various formulations the same as solid fertilisers. A general one would be marked as N7, P7, K7 on the bottle, a specialist rose fertiliser would probably be marked as N5, P7, K10.

They are especially useful for applying directly to the plant's leaves as a foliar feed. The plant takes the nutrients in almost instantaneously when applied in this manner. The feed can be applied either with a watering can or with a sprayer. A word of warning though, never foliar feed in direct sunlight as this will cause severe scorching to the foliage.

Home made Liquid fertilisers

Gardeners have for generations made their own liquid fertilisers. Any animal manure can be used but sheep manure is generally preferred. Comfrey is also very popular with gardeners. (See Comfrey Press) This is put into a hessian sack and suspended in a barrel of water. After a couple of weeks it is ready for use. For most applications it can be used neat but for should be diluted to half strength (mix with equal amounts of water) for foliar feeding or for use on seedlings. It contains about .8 % Nitrogen, .5 % Phosphorus and .4 % Potassium and a full range of trace elements. A tiny squirt of washing-up detergent in the spray reservoir will help the foliar feed to stay longer on the leaves for greater effectiveness.

© copyright 1999, P. A. Owen

UK gardening help and assistance