Using fertilizers

Plants, like people, thrive on a balanced-diet- the soil they grow in musThe enriched with all the foods needed for healthy growth.

P lants, unlike animals, are able to manufacture their own body-building substances from raw materials. Several of the essential chemical elements for plants are readily obtainable from the air and the soil and do not need supplementing under normal conditions – these are carbon, hydrogen and oxygen.

Other essential nutrients, dissolved in water, are taken up by hairs growing near the tips of the roots. The three principal elements on which plant life depends : nitrogen (abbreviated to N), phosphorus (P) and potassium (K) : are absorbed in this way. A well- tended soil will be rich in all these, together with the so-called ‘trace elements1. Trace elements are only required in very small quantities but are just as essential as the major nutrients. Nitrogen is ‘fixed’ in the soil and so rendered available to plants by the action of soil-borne bacteria. Nitrogen is also released when organic matter is broken down.

In time, plants can use up most of the available nutrients in the soil, so it is essential to supply more if they are to thrive. Nitrogen, for example, is leached rapidly from the soil by rain.

Chemical fertilizers can feed plants quickly, supplying nutrients in a form that can be absorbed immediately, so they are useful for treating nutrient deficiencies.

Organic gardeners prefer not to use man-made (sometimes called inorganic) fertilizers. The organic approach is to feed the soil rather than the plants, so organic gardeners concentrate on enriching the soil with garden compost or well-rotted farmyard manure.

However, it can take years to build up soil fertility in this way, so organic fertilizers derived from animal or plant wastes or naturally occurring minerals are used to counteract deficiencies in the soil.

Fertilizer types

Each of the essential nutrients – nitrogen, phosphorus (in phosphate) and potassium (in potash) – can be bought separately as so-called ‘straight’ fertilizers, or in balanced mixtures known as ‘compound’ or ‘general’ fertilizers. The latter often include trace elements too. Nitrogen sources One of the cheapest sources of nitrogen is the inorganic fertilizer sulphate of am-monia. Repeated applications of sulphate of ammonia will gradually make the soil more acidic. This could be a disadvantage if you grow brassicas, for example. In such circumstances, look out for nitro-chalk, which has added lime. Organic nitrogen fertilizers, derived from animals, include dried blood and hoof and horn.

When plants need a quick-acting stimulant during the growing season, it is usually best supplied by nitrogen alone. For example, spring cabbages respond quickly to a top dressing of a nitrate fertilizer at 15g (Vioz) per sq m/yard once growth starts.

Most fruit crops also appreciate a top dressing of sulphate of ammonia in spring.

Phosphorus sources Phosphorus, in the form of soluble phosphates, is particularly important to plants in the seedling stage and in the formation of seeds. When plants are growing in a soil deficient in phosphate, their leaves are smaller and a dull purple colour, and the growth of the plant slows down. Too much phosphate will cause a premature ripening of the plant.

Phosphate fertilizers include bonemeal, a popular and widely available organic fertilizer, and superphosphate of lime. Potassium sources Potassium, in the form of potash, increases the intensity of flower colour and is sometimes given as a top dressing to improve the formation and ripening of flowers. It hardens the plant tissue and so improves the plant’s resistance to pests and diseases.

Potash is especially beneficial for fruit crops, tomatoes and potatoes. Tomato feeds contain nitrogen and phosphate but a higher proportion of potash.

Light soils in particular are likely to need added potash, and the most suitable form for the gardener is sulphate of potash. Compound fertilizers The easiest way for most gardeners to apply nutrients is to use a compound fertilizer which contains all three major nutrients (NPK). Grow-more is a very popular inorganic compound fertilizer that supplies equal proportions of NPK.

Organic gardeners traditionally used blood, fish and bone. This is still popular but there are now other organic fertilizers, such as pelleted chicken manure, which contain high nutrient levels.

Many compound fertilizers are formulated for specific parts of the garden – lawns and flowerbeds, for example – and they are available as granules or as liquid feed. Slow-release fertilizers Many organic fertilizers, such as blood, fish and bone, release their nutrients slowly. But there are now inorganic fertilizers, such as Osmocote, which release their nutrients in a controlled way. The nutrients are held inside permeable membranes – as the temperature increases more fertilizer is re- leased. The granules are also available as plugs or tablets. These are an easy way to feed containers and hanging baskets, as the plugs or tablets are simply added when the containers are planted up. Liquid fertilizers Concentrated compound fertilizers, sold in both solid and liquid form, must be diluted before use. Once made up, they are easy to apply and are quickly absorbed by plants.

Some liquid fertilizers are derived from seaweed and humus extracts; others are made from chemical elements. Liquid fertilizers are often formulated for specialized uses, tomato feed being the most common example. 2 Foliar feeds Plants absorb nutri-:l ents fairly slowly through their r roots. Dilute solutions of liquid fertilizer sprayed on the leaves are absorbed more rapidly. Some fo-l liar feeding fertilizers are based on l soluble, inorganic fertilizers, while others are all organic preparations , with a seaweed base. E Foliar feeds should be regarded as a supplement to manures or fer-tilizers. They are particularly use-s ful, however, if the plants have a I poor root system or during dry spells when plants are more likely to have difficulty in drawing nutri-’ ents from the soil.

Applying fertilizers

Never apply more fertilizer than recommended. Measure roughly the area to be fed, then weigh the required amount of fertilizer on kitchen scales in a plastic bag. Halve the amount of fertilizer when farmyard manure or garden compost has been dug in.

A fortnight before sowing seeds, spread a compound fertilizer evenly over the soil and hoe or rake it in. Do not dig it in or it will wash down out of reach of the roots.

Apply top dressings along the sides of the rows or around plant roots and lightly hoe them in. Do not allow inorganic fertilizers -except foliar feeds – to touch the leaves or they will be scorched.

In dry weather, water in fertilizers – they cannot be absorbed by the plants until fully dissolved.

The condition of the soil and the weather also dictates which types of fertilizers are the most suitable to use. A light, sandy soil, for example, needs more potash than heavier soils, especially in gardens where soft fruits are grown.

In districts with a heavy rainfall, nitrogen fertilizers wash out quickly and should be replaced by regular top dressings.

Storing fertilizers

Keep fertilizers in their original container and store in a dry place as they quickly absorb moisture. Fertilizers should always be kept out of reach of children – some fertilizers are poisonous.

Sorry, comments are closed for this post.