Q: Mushrooms suddenly appeared on my tree’s trunk. How can I treat them to protect the tree?

A: Unfortunately, you can’t treat mushrooms growing out of wood, and the fungal growth that produced them has probably been present undetected for some time — months, or possibly even years. There are three general categories of fungus associated with tree wood: beneficial fungi (mycorrhizal), secondary fungal growth (passive consumers of dead wood), and pathogenic fungi (infectious initiators of wood decay).

Most fungi associated with trees are harmless or mycorrhizal in nature, helping the roots absorb nutrients and moisture, increasing tree tolerance to stress, and potentially even resisting infection. Mycorrhizal means “fungus root,” because it essentially forms an extension of the root system as the fungus grows. When the fungus is ready to reproduce, its mushrooms appear in the root zone of the plant it’s living with. Mycorrhizal fungi are abundant in the plant world.

Fungi producing mushrooms directly out of wood are another matter. Trunks, branches, and major roots with mushrooms sprouting out of the bark indicate that the wood underneath is decaying. Decay could be due to the action of the fungus itself, or from other causes prior to its arrival.

Neither removing visible mushroom growth nor treating the tree with fungicide will help. Wood decay can’t be reversed, though sometimes a tree can compartmentalize the damage, walling it off internally from spreading further. Even so, hollowed-out sections of wood that have less structural integrity can increase the risk of breakage later.

Dead and dying trees still provide great wildlife value, and any fungi involved won’t necessarily be a menace to nearby trees. If a declining tree’s eventual breakup or fall won’t endanger people or damage property, it’s both sustainable and economical to let them degrade at their own pace. Otherwise, sooner or later, tree removal will be necessary.

Q: The soil test for my lawn indicated that organic matter was low at 3%. Since Extension’s reference material says that 5% or more is a good goal, how do I add more?

A: Even a seemingly low 2% level of organic matter can be just fine for most soils, though vegetable gardens benefit from higher levels. Flower beds and vegetable gardens can have organic matter added as a periodic topdressing (an inch of compost applied yearly, for example). Or it can be applied indirectly as mulch breaks down over time, essentially composting itself.

Lawns would be smothered by similar application methods, so instead, the best approach is to use a mulching mower. These mowers chop-up the clippings into finer pieces instead of bagging them or leaving them behind as clumps of coarse material on top of the grass. That extra step of processing the clippings helps them to more easily sift back down between the grasses to lay on the soil surface.

Just like tree and shrub leaf litter left in flower beds, clippings compost in place, adding organic matter as organisms living in the soil till it in naturally. The process is circular, too — the more organic matter in the soil, the more likely you’ll have a healthy, diverse community of insects, microbes, and other organisms that break down plant debris like lawn clippings. As they tunnel through the soil, they improve aeration and drainage for roots and bring those recycled nutrients into the root zone. Since you’re conserving nutrients by keeping grass clippings in the lawn, and because organic matter helps the soil to retain nutrients, mulch-mowing reduces the turf’s need for fertilizer.

For areas of lawn needing renovation or patching, you can amend bare soil with compost to resist compaction, improve drainage, and to increase its nutrient-holding capacity.

Good quality topsoil will also contain some organic matter, and this can be used to help level out any lumpy spots where mowers cut the grass too high or short.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.