Garden Q&A: Be wary of the 'bathtub effect'

For The Baltimore Sun

I bought three of the same trees last year. All three bloomed this spring, but later one developed some dead limbs. Now the rest of the tree is wilting and dying. There are no signs of bugs, holes in the trunk or leaf spots. I thought it could be root rot due to the clay soil, but the other two continue to thrive right beside it in exactly the same conditions.

This does suggest a root problem. With heavy rains this spring, it may have succumbed to the "bathtub effect" and drowned. This happens when the planting hole drains so poorly that it fills with water for long periods and drowns the tree. It’s hard to believe that seemingly identical planting situations can in fact be so different, but see the photo where holes right beside each other drained very differently. We can’t see conditions below ground. Poor draining soils can be made worse when lots of organic amendments are added to the backfill soil. When there is very heavy rain, the water fills the planting hole readily because highly organic soil has large pores (spaces) between particles. But, then, the water may sit in the hole for days because it can't drain out into the clay soil fast enough. (Clay soil has tiny particles close together.) Thus, the plant drowns. When backfilling, use the native soil — even clay soil — that came out of the planting hole. A few handfuls of organic matter is all right. Rough up the side and bottom of the hole and spread out the roots.

I noticed webbing on branches of my blueberries with what looked to be dead bugs and dead leaves inside. I cut out and got rid of these branches. What is it and what should I do?

This is a fall webworm nest. The webworms are gone and only pellets of excrement remain in the web. Fall webworms (the name notwithstanding) have spring and fall generations, but the spring population is usually light and unnoticed. This year, their numbers are high. Webworms don't do enough damage to be significant, unless a plant is small. This is a native caterpillar and a great food source for birds. In general, you can cut the webbing out, or break it up and let the birds in. Or, you can manually pull it out and drop it into a bucket of soapy water to kill the caterpillars. If pruning out the nests removes too much of a small plant, manually pulling it out would be better. No insecticide is necessary.

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

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