Q: What’s growing on the trunk of my lilac tree? — Phyllis D.

A: Your photo shows mushrooms growing on the trunk, which are the visible, exterior "fruiting bodies" of fungi. Mushrooms generally live on dead or decaying organic material, and produce spores by which these fungi are spread.

Besides the visible mushrooms, these fungi have unseen rootlike structures, called mycelia, extending into the organic material on which the fungi are attached. When these mushrooms appear on tree trunks, mycelia are working internally in the trunk, and are usually a sign of dead or decaying tissue inside the tree.

Such fungi are normally secondary invaders, entering a trunk that was previously wounded by cracks, winter injury, pruning or other wood damage. I notice several cracks in the trunk and limbs, which might have led to injured tissue and moisture buildup — which was an invitation for secondary invading fungi to enter and begin the natural wood-rotting process.

There isn't a good way to stop the fungi after they start their activity, because the underlying problem of damaged wood remains. It might be wise to scrape off the mushrooms as best you can, but the interior mycelium growth will still be there, living on the decaying or injured wood, and more mushrooms will eventually appear. If any rotten wood can be removed with a sharp knife, it might help. Fungicides are generally preventative, rather than curing fungal problems already entrenched.

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Wood-rotting fungi are a part of the cycle of nature, helping to decompose dead wood, and when a tree enters this stage, reversal is rare. Trees can live with this condition for a time, and we see mushrooms growing on trees in forests. But it does signal a serious situation in which such trees likely won’t live to a ripe old age. I wish I had better news.

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Q: Should I rototill my vegetable garden in the fall after it is cleaned out? — Darwyn S.

A: I think it’s a good idea to rototill the garden in the fall, but it’s somewhat of a personal preference. Autumn is a great time to add organic material like leaves, peat moss or compost, and turning the soil helps the material to decompose. Rototilling or spading the soil helps expose insects and disease organisms that might be trying to overwinter underground, and turning the soil exposes them to possible winterkill.

Fall tilling tends to make the soil more workable in the spring, especially if the soil is heavy. Some gardens are successful with a no-till type of operation, and that’s an increasingly successful trend. I still favor fall and spring tillage for my own garden, partly because I enjoy rototilling and the aroma of freshly turned soil.

Q: We planted a purpleleaf sand cherry bush about five or six years ago. I didn’t realize how fast and how much it grows every year. I’ve been trimming it back at least 12 to 18 inches every spring after it bloomed. It has all of the new growth on top and only a few new branches at the bottom. Is there anything I can do to force it to fill out at the bottom? I read that I can cut it back in the early spring, but can I do that since it’s been in the ground this long? — Yvonne R.

A: Your purpleleaf sand cherry will rejuvenate nicely, and can be done periodically even when it gets much older and needs occasional re-working. Even though it was planted five or six years ago, you can cut it all the way down to about 6 inches above ground level around April 1 before new growth begins. That's the best time for such rejuvenation pruning.

Rejuvenation pruning will encourage vigorous new branches to sprout from the lower trunks, making the shrub fuller. Because these shrubs grow quickly, this rejuvenation can be done every four or five years, or whenever it looks "leggy." Spring is the preferred time for this, rather than fall.

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at donald.kinzler@ndsu.edu or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.