Mulching is useful throughout the garden: it reduces watering, feeds the plants, covers the ground and of course reduces the weeds. Whether it is in the form of dead leaves, grass cuttings (untreated), chipped bark or any other mineral matter, everything is good!
Under the mulch, the soil remains clear, becoming richer and loamier.
Multi use mulch
Apply a thick layer at least 5cm and up to 10cm thick, the mulch will cover the soil and prevent the weeds germinating as they want. It will encourage the existing plants, that will find extra moisture and food as the mulch slowly decomposes. Earthworms will adore it! The soil surface will become more alive thanks to the mulch. However, it is the fact that the soil is deprived of light that will stop the weeds growing. As the mulch starts to breakdown, the thickness of the layer will diminish. A little light will start to reach the soil, which will encourage the weeds to start growing through the thin layer of mulch. They are likely to grow quickly as they benefit from the favourable conditions that were previously reserved for the cultivated plants. The only way to stop this is to add more mulch.
Adding an extra layer of mulch
Do not wait until the weeds start growing through the mulch before adding some extra: get into the habit of topping up the mulch around the plants so that it is up to 10cm thick. So that the mulch can have the dual purpose of both suppressing weeds and feeding the plants, it needs to be soft: use dead leaves, straw, hay or grass cuttings. This will make it decompose quickly. If the mulch is (chipped bark, wooden sheets...) it will stop the weeds but starve the existing plants. Note that you can mix the types of mulch: some grass cuttings mixed with dead leaves, or mixing some straw with a small amount of wood chippings will do no harm, in fact the opposite!
A little point to note
Certain plants detest mulch, such as roses and citrus fruits because of their delicate roots. For these plants, it is best to stick to hand weeding or use ground-covering plants, which will spread outwards but not upwards.
On the other hand, other plants thrive with mulching: such as trees and other hardy plants that naturally grow in forests. These plants are used to profiting from the thick layer of dead leaves around their base. Where the soil is light, for example around the base of a hornbeam hedge, you could even use more than 15cm of mulch. The hedge would then look after itself needing no extra watering or fertilizer. Bracken, rhododendrons and bamboo also belong to this group. Of course, there are other cultivated plants that enjoy a good amount of mulch around their feet.
In rocky soil where there is not a lot of top soil, it will be in your own interest to mulch. As there is a shortage of soil, it will be the mulch that helps the plants establish, allowing them to develop their roots over a larger area. However, in heavy deep soil restrict the amount of mulch: too thick a layer risks suffocating the plant's roots.