Mulching is covering the soil with a layer of material for two main purposes, conserving moisture and preventing weeds. Mulches are placed on the surface of the soil, they can be organic, such as manure, grass clippings, leaf-mould, bark, straw or stalky material or non-organic, such as black polythene, stone chippings or crushed slate. Organic mulches have the advantage that they will be slowly broken down and taken into the soil, providing extra organic material (humus), which improves the water-holding capacity of the soil. Non-organic mulches are often laid on a porous membrane to stop them from becoming mixed with the soil.
The movement of water in soil is both upward and downward. The excess water gradually percolates down, and, if the drainage is perfect, is carried away. Because of the porosity of soil the water in it also rises - just a sponge stood in water. When the water gets to the top of the soil the wind and the heat of the sun evaporates it, and it is carried away. In this way soils can, in hot weather, soon dry out. To prevent this evaporation of soil moisture, mulching is carried out. This can take two forms:
- Continued cultivation of the top inch or so of soil - known as dust mulching.
- The application of some organic material - such as manure, grass clippings, leaf-mould, bark, straw, stalky material or Cocoa-shells (a by-product of chocolate manufacture) etc.
- The application of some non-organic material - such as black polythene, stone chippings or crushed slate etc.
Any of these methods has the same effect in helping to keep the water where it is required - around the roots of the plants.
Mulching is carried out during the summer months to retain the water in the soil, and it is not a substitute for applying rotted material in the late autumn or winter to condition the soil. There is no rush to mulch at the beginning of the year, the soil needs to be warmed before the mulch is applied.
Where mulches are applied, watering the plants can be a problem as the water has to penetrate the mulch before reaching the soil, burying inverted plastic bottles with their bases removed will provide a convenient method to get the water into the soil near plants. The buried bottles can be placed under foliage or behind spreading plants so that they are not unsightly.
When dust mulching in dry periods it is far better to hoe continuously than to water the plants.
Shredded stalky material can be used and is very good at keeping weeds down and improves the soil structure, but when the low plants were covered (such as an asparagus bed and dahlias), the plants can be slow to reappear in the spring due to slug damage, so shredded material better avoided if slugs are likely to be a problem. Long grass cut from the wilder areas can used as a mulch around many of fruit trees and around native trees planted in the wild parts of the garden. The strawy material from many plants at the end of the season can be collected and used as a mulch around trees nearby. Piles of thistles which have been pulled soon wilt into a black heap and even can be used.