Mouldy Mulch?

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Whether you’re an avid gardener or an occasional one, understanding mulch mould is important to keep your plants and garden healthy.

Most moulds and fungis are most apparent from April to October, and especially after a rainfall.

While bacteria and fungi are a naturally occurring part of the decomposition process, some moulds can become a problem for plants and cause diseases.


The most common way that mould occurs in mulch is a result of a layer of mulch that is too thick.

If mulch is too deep, it can heat up and dry out. Dry mulch is an ideal living space for fungi, turning it into a water-repellant, mouldy material. Repelling water prevents trees and other plants from getting the water they need.

Alternately, the soil underneath the mulch can stay too wet, leading to root rot.

This is especially problematic for the development of mycorrhizal fungi, which is extremely important for healthy plant root systems and overall plant health.

Instead, moulds like verticillium dahliae and rhizoctonia solan begin to grow, killing ornamental shrubs, vulnerable plants and seedlings.

Mouldy mulch can also result from already infested trees being made into mulch.

But there are ways to combat mouldy mulch!


Mulch should be applied in a 1.5-2 inch deep layer. This is ideal for keeping mulch at the right level of moisture while still allowing nutrients to penetrate into the soil and contribute to healthy plants.

Use mulch made from decay-resistant trees, like pine and cypress, whenever possible.

Additionally, mulch made from coarse wood products are less likely to have and develop mould and fungus problems than finely-ground wood products.

As soon as you put down mulch, give it a good soak with the garden hose. Mulch that has been stored in piles or in bags tends to cool down. Good microorganisms that you need for healthy plants thrive in warm, moist conditions, so soaking it first prevents mould and fungi spores from moving in.

Keep your mulch healthy and you’ll have a healthy garden!

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