Fertilizers are essential for heavy cropping of vegetables, especially on allotments where the same ground is cropped year after year, and in Greenhouses where crops are intensively cultivated. It is important to know the chemical composition of a fertiliser, in order to target the right type of fertiliser to the right plant. The main constituents of a fertilizer are Nitrogen (N), good for leafy growth; Phosphorous (P), good for root growth; Potassium (K), good for encouraging flowering and fruiting; and several trace elements. On manufactured fertilizers, you will find details of the % chemical composition written on the container in small print. A multipurpose fertilizer will typically have the composition of N 8%, P 8%, K 8%, plus trace elements. A high potash soluble fertiliser for use in a greenhouse will typically have a composition of N 5 %, P 5 %, K 10 %, plus trace elements. Fertilisers can release their chemicals either quickly or slowly, and they can be either organic or inorganic. There are various types:-
Organic Quick Release Fertilisers.
1. Manure. Often seen on allotments, it is best used when it has matured or aged, and lost the intense ammonia smell. It is best purchased or acquired in the Autumn, as it will have spent the Summer resting and breaking down, after the animals have been turned out to the grass after the Winter. Once the straw has composted down, it adds humus to the soil. As the main chemicals are Nitrogen and Potash, it is good for Potatoes and Brassicas. Chicken pellets or manure, are a more concentrated form.
Warning of aminopyralid contamination of manure!! Since 2008, there have been many reports from allotments of manure having been contaminated by residues of a herbicide called “aminopyralid”. For more information see the page on manure contamination with aminopyralid.
Warning of possible E. Coli 0157 manure contamination!! The Scottish Agricultural College has recently reported that the cattle on 1 in 5 farms in Scotland, are now infected with E. Coli 0157. This is the very dangerous bug which can cause severe illness and even death, particularly in the young and very old. This is a new hazard and there is some doubt as to how long the bug remains infectious in the cattle manure, but it could be several months. In the meantime, it would be sensible to wear rubber or PVC gloves and Wellingtons when handling manure in any way. Always thoroughly wash your hands before you eat anything at the allotment, and change your footwear before you leave the allotment. It might also be sensible to avoid growing salad crops in recently manured ground. The cooking process should destroy the germs on other vegetables.
Other quick release fertilisers include Blood fish and bone, Chicken pellets.
2. Organic Green Manures are plants that are grown purely to be dug back into the soil or seeped in water to provide a liquid fertiliser. The plants grown are usually Borage, Rye-grass, Comfrey, Forage Peas, Field Beans or Annual Lupins. Comfrey leaves can be used to create a liquid fertilizer. They can be sown when there is some spare ground, until it has to be used again for a food crop. Field beans and peas can be sown in the Autumn and dug-in during the following Spring.
Organic Slow Release fertilisers are Bone Meal, Seaweed meal, and Hoof and Horn.
Inorganic Fertilisers are generally quick or semi-quick release and the nutrients are readily taken up by the plants. A typical semi-quick one is the pelleted “Growmore”. A quick one is concentrated liquid tomato fertiliser.( you can also get organic liquid tomato fertiliser) Always remember to follow the instructions on the container. Too high a concentration of fertiliser will burn the plant roots.
Rock dust re-mineralisation. Consider using rock dust to renew trace elements where soils, such as in allotments, have been in intensive cultivation for many years. This can lead to depletion of trace elements. I have not tried it, but there have been good results in the Highlands of Scotland from using this technique on peaty soils.