Mulching is a technique consisting of covering the soil with organic or inorganic material to preserve humidity and improve soil condition. This technique can help in pursuit of different goals, from reducing evaporation, the control of weed growth, to protect roots from extreme temperatures fluctuation in summer and winter, to improve soil fertility and biology (especially with organic mulching) and to protect plant from certain diseases. It is especially useful in order to protect recent-planted trees from competition with weeds and in areas characterized by a high evaporation ratio. By mulching, natural forest environment is trying to be simulated. Indeed, in a natural forest, soil is covered by leaves, organic material and it is rich in living organisms that recycle nutrients.
It is important to carefully choose the type of mulch, by taking into account both plants needs and the material available on site, as well as the method of application because they can influence the health of the plants. There are many different types of mulch: organic mulch includes grass clippings, shredded leaves, wood chips, straw or hay, compost and coconuts. Grass clippings are the easiest way of mulching and they are rich in nitrogen. Shredded leaves are very rich in nutrients and improve soil fertility. Straw and hay are particularly efficient in saving moisture and in keeping weeds away. Lastly, compost is a good alternative because it improves soil structure; it is recommended to cover the spread compost with a layer of another mulch in order to keep the compost moist. There are also inorganic mulches such as gravel or stones. They don’t decompose and enrich the soil but they are pretty efficient in letting air circulate and letting water infiltrate in the soil beneath, while keeping weeds away.
Before applying mulch, it is important to determine whether plants or crops will benefit from mulching by determining if soil drainage is adequate. For well-drained soils, it is recommended to apply a layer of 5-10 cm of mulch and decrease it if soil is less permeable.
The base of the tree trunk should not be covered by mulch. Instead, it should be exposed, in order to prevent any disease due to excessive moisture.
Food and Agriculture Organization of the United Nations, 1991, Chritchley & Siegert, Water harvesting, http://www.fao.org/3/u3160e/u3160e00.htm. Reproduced with permission
WOCAT, 2012, Schwilch, Hessel & Verzandvoort, Desire for Greener Land, https://edepot.wur.nl/212528. Reproduced with permission.