Although mulch is a good thing, too much mulch creates a very wet environment which is favorable for mushroom growth. Mulch has many different natural benefits when used around plants and trees: it keeps the ground moist, holds in nutrients, keeps weeds from growing, and adds an aesthetic appeal. Traditionally, mulch is made from wood, but can also be comprised of other things like synthetics, rubber, stone, and other recycled materials. Although they do not harm plants, mushrooms in mulch can be unsightly.
Mulch in Moderation
There are times when you can actually have too much of a good thing. While having a layer of mulch around your plants, flowers, vegetable beds, and trees is a good thing, you can overdo it. Too much mulch around your plants can actually have a suffocating effect, where the roots will not get the nutrition they need.
Tip: Install raised beds for greater control over soil conditions.
Mushrooms thrive in wood or bark mulch. To avoid excessive mushroom growth, use organic compost instead of mulch. Since the materials in organic compost are already broken down, there's not as much decaying material for mushrooms to feed on.
Tip: Although some mushrooms are edible, never eat a mushroom unless you are certain it is edible.
Mushrooms like dark, shady places. If your trees are overhanging a lot, or the flowers and shrubs are causing some shade to cover the mulch, mushrooms can being to propagate. Prune your trees, shrubs, flowers, and other plants to keep them from overhanging or causing too much shade.
Use a rake and mix the mulch up. Move it around and loosen it up to let the mulch dry out and to create room for the plants to breathe.
Once the mulch begins to rot and deteriorate, it is time to get rid of it. Four things that mushrooms love are dense cover, a shady area, moist ground, and rotting vegetation, so removing these things will give you have a better chance of keeping your mulch free of mushrooms. If mushrooms have started growing, remove the entire mulch bed. Pick out the mushrooms and turn the soil. Then, add a new layer of two to three inches of fresh mulch.
As a last resort to getting rid of the mushrooms in your mulch, you can apply some fungicide. A general purpose fungicide will work well enough. However, if you want to keep the harsh chemicals out of your garden, use two tablespoons of baking soda per one gallon of water. Lime will also work well in getting rid of the mushrooms. Mushrooms like soil that is acidic, and the lime will sweeten the soil to get rid of them. The only problem is that this could have adverse effects on the other plants because of the change in the soil composition. It is better to use other methods first before using chemical remedies.