The art of mulching: how to protect your soil without harming your trees
In short: Mulching is a simple way to conserve water, suppress weeds, and improve soil health. However, using it incorrectly can create dangerous "mulch volcanoes" or invite pests to strip the bark off your trees. To do it right, you must understand the distinction between mulch and compost.
Mulch acts as a protective top layer of organic or inorganic matter. Its primary functions are to conserve moisture by reducing evaporation, suppress weeds by blocking sunlight, and provide a decorative finish. While organic mulches like wood chips or leaf mould break down to release nutrients and improve soil structure, non-biodegradable options like slate, gravel, or stone chippings do not boost fertility but remain effective for weed suppression and moisture retention. Common materials include garden compost, well-rotted manure, or even seaweed. You might also use straw, particularly for strawberry plants.
The material you choose can influence soil temperature. Dark-colored mulches absorb heat to warm the soil, whereas light-colored materials, such as white gravel, reflect sunlight to keep roots cooler during intense heat. For new beds, permeable sheets or woven landscape fabrics can be used, though they may require camouflage with decorative aggregates to improve aesthetics. It is vital to use permeable materials to avoid drainage problems and surface runoff. When using landscape fabric, you can make slits to allow for direct planting. Always ensure the layer remains permeable to allow irrigation to reach the roots.
When mulching trees, precision is essential. You should apply a layer—ideally about two inches thick—in a circle around the base. Crucially, the mulch must not touch the tree trunk. Piling mulch against the bark invites insects and small animals, such as voles, to enter and strip the bark. Furthermore, avoid the common mistake of continuously topping off old layers, which creates an inclined mound known as a "mulch volcano," a practice that is unnecessary and harmful to the tree. Timing is also key, with mid-to-late spring or autumn being ideal for application. New plants can be mulched at any time of year if they require moisture retention.
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Sources
- Summary by Intellect · source: How to Mulch a Plant | Lawn & Garden Care
- Also: www.rhs.org.uk — Mulches and Mulching | RHS Advice
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