General fertilisers | Special purpose fertilisers | Straight fertilisers | Manures
A general fertiliser provides the three major nutrients – nitrogen, phosphorus and potash – in correct balance and it is suitable for general garden use to improve basic soil fertility. The formulae vary between the various brands: 7:6:17, 5:5:10, 10:10:20, 7:7:7. General fertilisers include Vegyflor, Growmore, John Innes Base Fertiliser, Potato and Vegetable Fertiliser and Potato Fertiliser.
Special purpose fertilisers
The special purpose fertilisers also provide all the major nutrients, but some of the minor ones too, and the balance of nutrients is set to suit the specific needs of certain plants, or groups of plants.
Purpose-made lawn fertilisers, such as Goulding’s Lawn Feed Special, Lawnsman Spring Feed, Lawnsman Winterizer, Special Lawn Fertilizer, Lawn Food, Toplawn and Autumn Toplawn are specially balanced for grass growth. The spring lawn feeds suit the spring and summer needs of grass. The autumn feeds suit the autumn and winter needs.
Rose fertilisers, such as Goulding’s Rose Fertiliser, Toprose, Rose Food, Rose ‘Plus’, and Special Rose Fertiliser have matching amounts of nitrogen and potash – nitrogen for growth, potash for flowers. Tomato and fruit fertilisers – Liquid Tomorite, Tomato and Fruit Fertiliser – have a balance towards potash.
The straight fertilisers contain just one major nutrient. Sulphate of potash contains just potash. Sulphate of ammonia, urea and C.A.N. contain only nitrogen, and superphosphate contains just phosphorus. These can be used on their own where plants need only one of the major nutrients.
For example, lawns may not need phosphorus or potash, just nitrogen, so sulphate of ammonia (or urea or C.A.N. on large areas) would do. Fruit trees may not need further boosting by nitrogen, being already too vigorous. An application of sulphate of potash would balance vigorous growth, and encourage fruiting.
The straight fertilisers can be mixed together to provide general fertiliser, or any specific formula as required needs are detected.
Organic manures have the dual effect of improving soil structure, by adding humus, and improving soil fertility by adding both major and minor plant nutrients. Farmyard manure contains the three major nutrients in small but significant amounts, and a full range of minor nutrients.
Garden compost contains a range of nutrients similar to farmyard manure, but in lesser quantity. Mushroom compost is at least as rich as farmyard manure, but contains a lot of lime. Meat-and-bonemeal contains nitrogen and phosphorus, but no potash. Leafmould had some nitrogen and potash.
Wood ash has some potash. Seaweed has considerable quantities of minor nutrients. Peat has very little fertiliser value, and is used solely for its fibrous organic matter. These manures do not have enough fertiliser value to improve soil fertility quickly, unless they are used at high rates.
For instance, farmyard manure or mushroom compost might have to be applied at rates of up to 25 kilograms per square metre to bring up soil fertility to an adequate level for vegetable growing. An annual application of 4 – 5 kilograms of farmyard manure per square metre is the equivalent of the recommended application of general fertiliser.
Artificial fertiliser can be used in conjunction with manures, but the two should not be mixed, unless the manure is very well rotted. Scorching of the plant roots and lower leaves can result as ammonia is released.