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Garden Q&A: Moldy soil hardly unusual

| Saturday, March 9, 2013, 9:00 p.m.
Check for slugs at night when they're active. Jessica Walliser

Question: We moved into our home in the fall of 2010. There was black fabric covering the ground with soil and mulch on top. We removed the fabric and found a white mold covering the ground, so we removed most of the soil that was moldy.

In 2011, we planted perennials and annuals and for the past two seasons many of the leaves have had holes but we don't see any insects on them. I sprayed a bug spray but it didn't seem to help much.

Could the vegetable peels I've been burying be causing the problem? Could the mold be causing the problem? Is there a spray I could use that would not harm the butterflies and hummingbirds?

Answer: Wow. You have a lot going on in your yard. Hopefully, I'll be able to provide you with some answers.

Let's start with the mold you discovered growing on the soil. This is not at all unusual. When gardeners use black landscape fabric or plastic mulches, it blocks the light from the soil, prevents air circulation and creates a very dark, damp place — the perfect conditions for growing mold and fungi. The white substance you found was probably nothing more than fungal hyphae probing the soil for organic matter to decompose. Soil molds and fungi are as much a part of the garden's ecosystem as plants, birds and insects and, in general, they are nothing to worry about. Simply removing the fabric and exposing the area to light and air is usually enough to eliminate them. You would not have had to discard the soil, and I doubt that the previous presence of fungi has anything to do with your chewed foliage.

Secondly, burying your vegetable peels is a fine idea. In fact, I just addressed this very topic in my March 2 column. You can access the article online at to read more about the practice and its benefits. Again, I doubt the buried veggie scraps have anything to do with your current problem.

And lastly, know that spotting some holes in leaves is generally not a cause for alarm. There will always be insects in the garden, and we should never aim to completely eliminate them. Only when the damage becomes intolerable do we need to take action, and it is only rarely that a pest insect will actually kill a plant. (It is not in their best interest, after all, to kill their food source.)

If you do find the damage intolerable, your first step is to always, always, always determine exactly who the culprit is before applying any product. This means carefully examining the entire plant (including the leaf undersides) both during the day and at night, as many common pests are nocturnal feeders. If you still don't see any insects, take a damaged leaf in a sealed plastic baggie to a good, local garden center or to the Penn State Extension Service office for a proper identification of the pest. Only then can you know the appropriate way to attack your problem.

In your case, I suspect that slugs may be at least part of the problem. I see in your picture that your garden is shaded by the woods and that you have a lot of hostas. Hostas are notorious for being a favorite food source for slugs. And because slugs feed only at night, it makes sense that you haven't seen them. Plus, as mollusks not insects, they are completely unaffected by bug sprays of any sort.

This season, check for slugs at night and be on the lookout for the slime trails they leave behind. If you discover they are in fact the culprit, you can help control them by using slug baits with iron phosphate as the active ingredient. Avoid baits with other active ingredients as they may be toxic to dogs, cats, kids and other wildlife.

Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is

Send your gardening or landscaping questions to or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.

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