Feeding Vegetables and Fruit
Plants, like people, thrive on a balanced diet. Just as a well-planned meal contains proteins, carbohydrates and vitamins, a well-tended soil is rich in all the foods that plants need.
The chemical elements that are essential for healthy growth are taken up by the plants in two ways: Carbon, hydrogen and oxygen are absorbed from both the atmosphere and the soil.
Other nutrients, dissolved in water, are taken up as a ‘drink’ by hairs growing near the tips of the roots. The three principal elements on which plant life depends — nitrogen, phosphorus and potassium — are absorbed in this way.
Nitrogen promotes the growth of leaves and stems. A nitrogen-rich soil is ideal for growing such plants as cabbages, celery, leeks, lettuces and onions. It soon gets washed out of the soil, however, and supplies must be renewed every year.
Phosphates are necessary for vigorous root development. They also play a part in the growth of plants and the production of flowers and seeds.
Root crops, such as carrots, parsnips, swedes and turnips, do best in a soil with a good phosphate content. Phosphates remain in the soil as a plant food for two or three years after application.
Potassium, or potash, is vital for maintaining growth and for providing plants with resistance to disease and adverse conditions.
It contributes to the building up of starches and sugars in vegetables, especially in potatoes, carrots, parsnips, beetroot and sweet corn. Potash is also needed by all soft fruits. It stays in the soil for two or three years after application.
As well as the three principal nutrients, plants need magnesium, sulphur, manganese, iron, boron, zinc, copper, chlorine and molybdenum. These are known as trace elements, because only minute quantities — or a trace — are taken up by plants.
Finally, plants and soils require differing amounts of calcium, or lime.
With the exception of lime, all the complex needs of a plant could be met by enriching the soil with farmyard manure, which consists of animal droppings mixed with straw or other litter.
The highly productive kitchen gardens of Victorian times received huge quantities of stable manure, and the natural processes of the soil, assisted by enough lime to keep it ‘sweet’, made it unnecessary for the gardener to worry about details of plant nutrition.
This simple method of maintaining fertility is no longer practicable for most gardeners, who must now rely on whatever organic material is available and on supplementing it with chemical fertilisers.
Organic manures are composed of decaying matter — plants that are decomposing or that have been digested by animals. In the soil they are converted into plant food by a teeming population of fungi and bacteria. Organic manures feed the soil and, through the soil’s natural functions, the crop. They are slow-acting, and improve the structure of the soil and build up fertility from year to year.
Inorganic fertilisers feed crops more directly, supplying nutrients that a plant can absorb immediately. But they do nothing to improve the soil and may even deplete its reserves of organic material.
Aim to strike a balance, adding as much organic manure as you can find, and using fertilisers to remedy known deficiencies.
Two types of organic manures are used in the garden — for different reasons.
Bulky farmyard manures are dug in during the winter or are used as mulches in summer. Some are rich in plant foods while others have little immediate food value, but all add to the soil’s humus content and improve its condition.
The second type of organic manure consists of processed materials, such as bonemeal and dried blood. These are concentrated foods, generally used as pre-sowing dressings or as top-dressings for growing crops. They add very little humus to the soil. Bulky manures include:
Town gardeners may find that the compost heap is their only source of bulky, organic material. However, well-made compost can be twice as valuable as farmyard manure in its content of plant foods.
Stable and farmyard manures
Horse manure is ‘hot’ — that is, it ferments rapidly — and for this reason was at one time widely used to form hot-beds for raising early crops. Nowadays, electric soil-warming cables are more likely to be used instead.
It is one of the richest and driest manures, but often that sold by riding stables contains mainly urine-soaked straw and a few droppings; it decays rapidly into a disappointingly small heap.
Pig manure is slow to ferment and, when fresh, tends to be caustic and to burn the roots of young plants. It is best composted with straw and left for at least three months before use.
Cattle manure containing straw from the yards is wetter, and lower in nutrients, than horse manure. But it decomposes slowly into the soil, and is ideal for sandy soils.
Spent mushroom compost
Mushrooms are grown commercially on a compost based mainly on horse manure. It is carefully prepared to produce a controlled temperature over a period as the crop matures.
When all the mushrooms have been harvested the compost is sold either in bulk by the cubic yard, or, more expensively, in pre-packed bags that can be carried in a car boot. This is a good garden manure or mulch, containing humus and plant foods. It also contains chalk, which makes it less suitable for soils that are already alkaline though it will probably not do much harm unless applied every year.
Deep litter poultry manure
Partly rotted litter from poultry houses may be bought by the load from poultry farmers, but it is unsuitable for gardeners living in built-up areas. The manure is usually dry and dusty and must be composted before use.
It takes some weeks for the wood shavings or straw on which the manure is based to break down. During this time the heap may develop an offensive smell; so even in a country garden it should be placed as far away as possible from houses.
When composted, deep litter poultry manure is rich in nitrogen but deficient in potash and phosphates.
Although leaves of all types can be composted, the best quality leaf-mould is made from oak and beech leaves.
Place alternate layers of leaves and soil, each about 2in (50 mm) deep. A sprinkling of general fertiliser on each layer of leaves will assist decomposition. Do not make the heap more than 3 ft (1m) high. Turn it at two or three-month intervals.
The compost will be ready in about a year. Apply at the rate of 5-6 lb per square yard (2.5-3kg per square metre).
Large breweries sell their hop waste to fertiliser firms, who improve its nutrient content before selling it in bags as hop manure. It is excellent manure, but expensive to use in large quantities.
Some smaller breweries are prepared to sell the spent hops cheaply to local gardeners who provide their own transport. These untreated hops help to improve the physical condition of the soil, but they are low in plant nutrients. This can be remedied by using them in conjunction with a general fertiliser.
Other bulky manures, which can be obtained only in certain areas, include seaweed, municipal sewage sludge and wool shoddy.
This is rich in plant foods, especially nitrogen and potash, and breaks down quickly into humus.
Stack for a month or two to allow rain to wash out most of the salt, then dig it in at the rate of about 12 lb per square yard (5.5kg per square metre).
This well-balanced manure, which is processed by some local councils, is generally inoffensive to handle.
Ask the council’s Engineer’s Department if it is available in your area.
A traditional manure in parts of Yorkshire, shoddy is the waste from wool factories. Transport costs have now made it uneconomic to use at any distance from the factories.
Shoddy contains up to 14% nitrogen, which it releases slowly over about three years. Dig the manure in, without first decomposing it, at the rate of about 1 lb. Per square yard (500g per square metre) .
Among concentrated organic manures that are rich in plant nutrients but which add little or no humus to the soil are:
Dried poultry manure
Being extremely rich in nitrogen, this manure is best used sparingly with bulky material such as peat. Also, use as a compost activator.
Animal bones, ground coarsely and sold as bonemeal, or ground more finely and sold as bone flour, provide a steady source of phosphates to the soil.
Bonemeal releases phosphates slowly over at least two years, while bone flour acts more quickly but loses its effect within a year.
Work in coarse bonemeal, therefore, at the rate of 4-6 oz per square yard (120-180g per square metre) before planting fruit trees and bushes.
Before sowing or planting vegetables, rake in 4 oz. of bonemeal per square yard.
Hoof and horn
This is the main source of nitrogen in John Innes potting composts. It releases nitrogen slowly over a long period but its cost is about double that of sulphate of ammonia or nitrate of soda, the two main inorganic sources of nitrogen.
A quick-acting nitrogenous manure that can be used as a substitute for sulphate of ammonia or nitrate of soda. Use along a row of vegetables as a top-dressing at the rate of 1oz per yard run (30g per metre).
Although an excellent plant food, fish meal is now scarce and expensive. It contains no potash, but generally manufacturers remedy the deficiency by adding sulphate of potash. This will be stated on the packet.
Before sowing, rake in fish meal at the rate of 3 oz per square yard (90g per square metre).
Chemical or ‘artificial’ fertilisers are divided into those classed as `straight’, each containing one or two of the three main nutrients, and those that are ‘complete’ or `compound’ and provide a balance of plant foods. Straight fertilisers include:
Sulphate of ammonia
This nitrogenous fertiliser can be raked in before sowing at the rate of 1 oz to the square yard (30g per square metre) or used as a top-dressing for growing crops, especially cabbages and related crops, and salads, at the same rate, or at a oz per yard run of the row (15g per metre).
The effects of using sulphate of ammonia can usually be seen within 10-14 days.
When used alone, sulphate of ammonia tends to make soils acid. It therefore works better on chalky or well-limed soils.
Best of all, use it with superphosphate and sulphate of potash to make up a compound fertiliser (see next column).
Nitrate of soda
This quick-acting nitrogenous fertiliser is often used as a stimulant for growing crops, especially where plants have been checked by bad weather. Apply 1 oz per square yard (30g per square metre) .
Another nitrogenous fertiliser, Nitro-chalk is useful on acid soils because it does not make the ground sour. Use only as a top-dressing, at 1 oz per square yard (30g per square metre).
The most popular fertiliser for supplying readily available phosphates, it is usually raked or forked into the soil at sowing and planting times at the rate of 2-4 oz per square yard (60-120g per square metre).
It is too slow-acting to be used as a top-dressing but it remains in the soil as a plant food for some years.
Sulphate of potash
This is the most popular fertiliser for supplying potash, because it can be used safely on all plants. Apply it as a top-dressing at the rate of 1-2 oz per square yard (30-60g per square metre) over the rooting area of fruit trees and bushes, and along rows of plants that will be in the ground for a long time.
It may be mixed with sulphate of ammonia and superphosphate to make a compound fertiliser (see below).
Muriate of potash
More concentrated than sulphate of potash, this fertiliser may damage strawberries, red currants, gooseberries and tomatoes.
On other plants and bushes it can be applied as a top-dressing at the rate of 1-2 oz per square yard (30-60g per square metre).
Plants need a balance of nutrients. Proprietary compound fertilisers contain the three main nutrients — nitrogen, phosphate and potash — plus traces of minerals such as magnesium and iron. The rate of application of compound fertilisers is generally given on the bag or carton.
To make up a balanced fertiliser, mix thoroughly 4 lb (2kg) sulphate of ammonia, 5 lb (2.5kg) superphosphate and 2 lb (1kg) sulphate of potash. For most purposes apply at 2 oz per square yard (60g per square m).
Concentrated compound fertilisers, sold in both solid and liquid form, must be diluted before use. They are easy to apply as a top-dressing and are quickly absorbed by plants.
Some liquid fertilisers are derived from seaweed and humus extracts; others are made solely from chemical elements.
They are mixed in various proportions to give a wide range of analyses to suit the needs of various plants and soils.
Plants take several days to make use of nutrients absorbed through their roots. However, if their leaves are sprayed with dilute solutions of fertilisers the process is accelerated.
Special fertilisers for foliar feeding are obtainable at garden centres and from horticultural suppliers. Some are based on soluble, inorganic fertilisers while other all-organic preparations have a seaweed base.
Foliar feeds should be regarded as a supplement to manures or fertilisers rather than as the sole means of feeding the crop. They are particularly useful, however, if the plants have a poor root system or during dry spells when the plants have difficulty in drawing nutrients from the soil.
Storing and using fertilisers
It is cheaper to buy fertilisers in bulk than in small quantities, but the saving will be lost if they are spoiled due to careless storage.
Store fertilisers in a dry place as they quickly absorb moisture from the atmosphere and become either a sticky mass or set into a solid block.
Do not store paper bags on concrete or against walls. It is best to keep fertilisers in plastic bags or in covered tins.
Do not apply more fertiliser than recommended. Measure roughly the area to be fed, then weigh the required amount of fertiliser on a kitchen scale. Halve the amount of fertiliser when farmyard manure or garden compost has been dug in.
A fortnight before sowing spread a general fertiliser evenly and hoe or rake it into the surface. Do not dig it in or it will soon wash down out of reach of the roots.
Do not scatter fertilisers along a seed drill as they may injure the germinating seedlings. Apply top-dressings along the sides of the rows and lightly hoe them in. Do not allow inorganic fertilisers —except the special foliar feeds — to touch the plant’s foliage or it will be scorched.
In dry weather follow the application of fertilisers with a good watering because they cannot be absorbed by the plants until they are dissolved.
The condition of the soil and the weather also dictate the types of fertilisers 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, nitrogenous fertilisers wash out quickly and should be replaced by regular top-dressings of sulphate of ammonia or nitrate of soda.