Many materials are used as mulches, which are used to retain soil moisture, regulate soil temperature, suppress weed growth, and for aesthetics. They are applied to the soil surface, around trees, paths, flower beds, to prevent soil erosion on slopes, and in production areas for flower and vegetable crops.
They are applied at various times of the year depending on the purpose. Towards the beginning of the growing season mulches serve initially to warm the soil by helping it retain heat which is lost during the night. This allows early seeding and transplanting of certain crops, and encourages faster growth. As the season progresses, mulch stabilizes the soil temperature and moisture, and prevents the growing of weeds from seeds. In temperate climates, the effect of mulch is dependent upon the time of year they are applied and when applied in autumn and winter, are used to delay the growth of perennial plants in the spring or prevent growth in winter during warm spells, which limits freeze thaw damage.
The effect of mulch upon soil moisture content is complex. Mulch forms a layer between the soil and the atmosphere which prevents sunlight from reaching the soil surface, thus reducing evaporation. However, mulch can also prevent water from reaching the soil by absorbing or blocking water from light rains.
In order to maximise the benefits of mulch, while minimizing its negative influences, it is often applied in late spring/early summer when soil temperatures have risen sufficiently, but soil moisture content is still relatively high.
Using mulch is a good gardening habit but not mandatory; the benefits, however, make it worth the effort.
A really good job of mulching your garden usually offers these benefits:
- Inhibits weed germination and growth. (Weeds are not only unsightly, but they also steal resources from desirable garden plants!)
- Holds in soil moisture, protecting your plants from drying out quickly
- Moderates soil-temperature fluctuations (This benefit is especially valuable during that turbulent-weather period in spring when you don’t want your plants to be stressed.)
- In cold-winter areas, protects plant roots from winter cold and helps prevent frost-heaving, in which plants are literally pushed out of the ground by the natural expansion and contraction of the soil as it cools off and heats up
- In hot-summer areas, helps keep plant roots cooler
- Depending on what you use, adds a bit of welcome nutrition to your garden as it breaks down
The type of mulch one uses will depend on the function and the aesthetic value of the landscape –
Organic mulches such as compost, bark, wood chips, leaves, seed hulls, grass clippings, nut shells, newspaper, cardboard, or straw have the added benefit that they add nutrients to the soil as they decompose. This type of mulch needs to be periodically reapplied.
Inorganic mulches such as gravel, black plastic, or fabric perform many of the same functions as organic mulch but do not add organic matter to the soil.
Mulches should be applied evenly around trees, shrubs, and perennials, but never deeper than 10 centimeters. Mulch should be kept about 1 centimeter away from the main stem or stems of a plant and should never be piled against the trunk or over the top of a plant. For plants or trees in the lawn, a 1 to 2 meter ring should be applied extending out from the trunk, whereas for plants in beds it is best to mulch the entire bed.