Improving the soil FAQs

The soil in my borders dries out rapidly whenever we get a speli of fine weather. Is there anything I can do to prevent this happening?

There may be a mineral or mechanical pan below the surface that restricts the upward movement of moisture from below (it could also cause waterlogging in heavy rains). Dig down and, if a pan is present, break it up by forking or, if it is very hard, by use of a crow-bar. Light sandy soils, and those containing gravel, often drain too rapidly. If this is the case, dig in plenty of bulky organic material such as well-rotted garden compost or farmyard manure to help retain moisture.

A layer of the same sort of material, or of peat, leaf-mould, or composted bark, can also be placed on the surface around plants before the soil dries out. Such a layer is called a mulch. It also helps to retain heat, especially if a dark-coloured mulch is used, and discourages weed growth. Other materials that can be used as mulch include polythene, bracken, spent-mushroom compost, straw, spent hops, and grass clippings, although the last should be used sparingly. Organic mulches of plant materials can be dug in during the autumn to enrich the soil.

How can I stop moss from growing over my soil?

Moss will grow over any bare surface, particularly if the surface is compact. Hoeing and raking off is a temporary cure, although the problem is often worse afterwards because small pieces of moss come away and grow faster than ever. The best remedy is to encourage an open, well-drained soil surface by laying a bulky organic mulch over the ground. Extremely acid soils are especially plagued by moss; the application of lime will reduce the acidity, but do not put it on at the same time as bulky manure. Moss also favours soils that are in the shade.

What is humus?

Humus forms when the remains of dead plants and animals decompose as a result of the action of soil bacteria. A well-matured garden-compost heap is well on the way to becoming humus, and when such compost (or any other bulky organic material) is dug into the ground it will decompose further. Sooner or later, depending on soil moisture and temperature, the material will become a dark brown colour and sticky, and then it will turn black.

Humus constantly releases nutrients into the soil that are taken up by plants. It greatly improves the structure of soils: it enables the particles of light sandy soil to stick together to form crumbs, so that moisture and plant foods are conserved for the use of plants, rather than draining away; and it opens up the structure of heavy soils such as clay, so makirig cultivation much easier.

How can I make a compost heap?

Good garden compost results from careful stacking of vegetable and other organic waste. The heap should be kept moist without being too wet, so that conditions favour the requisite bacteria. Bacterial action in the heap increases its acidity, so a sprinkling of lime is necessary over each 300 mm (1 ft) depth as the heap is made. Bacteria require nitrogen, so the heap should also be sprinkled with sulphate of ammonia. Keep these two additives apart by treating each 150 mm (6 in) depth with one or the other. (You can, alternatively, buy special compost activators that trigger the bacterial process.) Enclose the heap in a 1.2 m (4 ft) square frame of wire netting, timber slates, or corrugated iron, and provide a cover to keep out heavy rain. Special composting bins are available for smaller gardens. The compost will be ready for use in about six months.

What is the value of farmyard manure?

A sample of farmyard manure typically contains straw saturated by animal urine and droppings. If stacked in a heap, it will heat up by bacterial action and eventually rot down to a friable (crumbly) texture. Farmyard manure contains some plant foods, but its main purpose is to improve soil texture. It binds light soil particles together, making them more retentive, and it opens up heavy soil.

If you have bought some farmyard manure, shake out the heap from time to time and add water to keep it moist. When you turn the manure over, the outside of the heap should be placed in the centre and vice versa to ensure even rotting. Never apply manure straight from the stable to your soil. If the manure was already well-rotted when bought, however, it should be shaken out with a fork and dug into the soil as soon as possible. For deep-rooting plants it should be dug well down.

What is green manuring?

Seed of a quick-maturing crop such as mustard and rape is sown thickly on vacant ground, and the resulting crop is dug into the soil while it is still soft and before it forms seed. For the small garden, grass is an ideal plant for this purpose, although grass seed is rather expensive.

Green manuring is beneficial because it takes up residual fertiliser which might otherwise be leached from (drained out of) the soil; the root action of the growing crop improves soil structure, and its foliage rots down to make humus.

Is seaweed a good manure?

Provided it is unpolluted by oil, seaweed is a valuable source of plant foods, especially trace elements such as iodine. Although it may be dug straight into the garden in small quantities, seaweed is better mixed with other plant debris and decomposed before digging in . If sufficient quantity is available, seaweed can be dehydrated by spreading it over the ground and turning it over with a garden fork from time to time. When dry it is burnt, and the resulting ash makes a very good fertiliser used at the rate of 112 g/m2 (4 oz per sq yd).

Can I add straw directly to the soil?

Undecomposed straw can be dug into the soil provided nitrogen is added at the same time. Straw contains less nitrogen than that required by bacteria to decompose it, so 0.4 kg (1 lb) of sulphate of ammonia should be added to each 50 kg (110 lb) of straw. Lime is also required at the rate of 2.5 kg (5.5 lb) ground limestone per 50 kg of straw.

Straw is a valuable source of humus and is more usually rotted down with lawn clippings and other vegetable matter in the compost heap; the heat generated will kill some of the unwanted seed left in the straw.

Which is the best kind of animal manure to use?

All animal manure is beneficial. Poultry and pigeon droppings contain the highest concentration of plant foods, and great care is needed to use them sparingly or they may scorch plants. They are best dried and used as fertilisers. Sheep manure is also a rich source of plant foods and used to be mixed with water to make a liquid feed. Horse manure is next in order of plant-food value, and when mixed with straw bedding it is ideal for digging in. Cow and pig manure contain relatively little plant food and tend to be too moist for use in all but sandy soils.

Can I dig established turf straight into the ground?

Yes—the fibrous roots of grass plants are excellent for improving tilth, while plant remains at various stages of decomposition will also be present; the grass top-growth too, will add humus to the soil.

If turf is dug in to the soil during active growth, it may re-grow (and so become a weed). If this happens, use one of the quick-acting total weedkillers that become inactive as soon as they touch the soil, before digging in the turf. The turf must be chopped up and turned grass-side down.

How can I prevent the soil surface from becoming hard after heavy rain?

Soil containing a high proportion of clay packs down during rain. The minute soil particles cement together, and they will prevent seeds germinating and also hinder the growth of established plants because the soil will lack oxygen. The hard surface ‘pan’ is caused by the lack of organic material in the soil. The remedy is to fork peat, composted bark, or other bulky organic material into the surface. A surface mulch of the same material will also help.

What can I do to prevent deep cracks from appearing in the soil during dry weather?

Evaporation of moisture from clay causes the soil to shrink. The trouble is cumulative because the deep cracks will allow further moisture loss from the subsoil reservoir. Mulch the surface with a bulky organic material. This is best carried out during the spring when the soil is still moist; worms will eventually carry the material down into the soil. Take every opportunity to incorporate compost when cultivating the soil.

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