Mulching is a by far the easiest and most effective way to protect almost any garden against dry weather and extreme conditions. A well-planned mulch is spread to trap rainfall and store it in the soil where plants can use it over dry periods. Many mulches are used to shade and cool the soil creating alpine or woodland conditions. Other mulches like
Weedmat or black plastic are used to trap the suns' radiant heat in the soil as well as holding in all available moisture like a cover does over a pot of boiling water. Stones and gravel act in much the same manner but to a lesser degree. Organic mulches like compost, aged manure, leaves, straw, hay, silage, sticks, lawn and hedge clippings, sawdust and bark actually feed the top soil while protecting the ground from drying out. All mulches hold down weeds thus eliminating a lot of garden maintenance. Weeds, especially those with runners or deep tap roots, draw a lot of precious water out of the soil.
The depth and type of mulch is dependent on the type of plants grown, the microclimate of the garden beds, and to a lesser degree the style and lay-out of the garden. Gardens in windy, exposed coastal situations, hot and dry areas, and lighter soils or soils that drain very quickly often need deep mulching. So do many fruit trees, woodland gardens, and garden beds planted with shallow or surface rooted plants.
As a general rule all exposed soil should be covered with some sort of mulch to capitalise on whatever rains do fall. Even gardens planted with hardy natives, South African, Australian or other arid zone plantings need some protection again drying out. Often these arid gardens are covered in weedmat, or less effectively in black plastic, which is then covered with a shallow layer of bark, pebbles, gravel, stones or sand, or other mulching material.
This keeps the soil warm and uniformly moist while allowing good drainage which is essential to the success of arid gardens. Avoid deep, heavy, wet mulches in arid plantings. Be sure that any mulch stays off the trunk, canes, or main stems at or near ground level. Rot or borer attack often occur when a heavy mulch builds up against an exposed trunk.
Mulching should start immediately if all available winter and spring rainfall is to be captured. Start the winter mulch off fairly lightly at a few centimetres in all beds where sun and warmth are necessary to plant growth and health ( arid, most annual and vegetable plantings). Progressively build up this layer as the season advances.
A spring mulch of 20cm or more would not be excessive for such vulnerable plants as daphne, hydrangea, vireyas and most rhododendrons, azaleas, pieris, camellias, gardenia, and any water-loving or woodland tree, shrub, and many annual or perennial plantings. In the vegetable patch the wisest gardeners cover beds with Weedmat or black plastic over winter to heat the soil then either remove this and/or cover the beds deeply with a water-retentive organic mulch for summer. Let the individual character of the garden dictate the mulch but get started!