In nature, plants drop leaves, twigs and branches onto the soil below them. This layer of matter protects plant roots from heat, cold, and drought. It also enriches the soil and controls weeds. If we mimic nature and apply a layer of mulch to the surface of our soil, our landscapes can benefit the same way.
Generally create a layer of mulch about 7.5cm (3") thick. Too much mulch will limit the air flow to the plant's roots. Too little won't control weeds. To prevent disease problems, keep mulch away from trunks of trees and stems of shrubs.
It is best to mulch in the spring after the soil has absorbed winter moisture, but before summer temperatures rise high enough to start pulling the moisture back out from the soil.
Organic mulch must be renewed periodically, as it breaks down after a period of time. It ads nutrients to the soil and improves soil structure as it decays. Types of organic mulch include bark, compost, composted sawdust, leaf litter, grass clippings, shredded newspaper, and woodchips.
Inorganic mulch, depending on the colour, can cause heat buildup in the soil and around plants, which can then increase water requirements. It should be used carefully for this reason. Avoid plastic or other impermeable materials which restrict the flow of water inot hte soil. Types of inorganic mulch include crushed gravel, lava rock, river rock, and pea gravel.