Ask the Gardener: Get rid of fungus gnats before bringing your plants indoors

Ask the Expert Gardening
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What to do this week: More plants die from thirst than hunger. Forget about fertilizing and instead water, water, water! It’s the only thing you really need to do during the dog days of summer. Don’t forget to irrigate the root zones of trees, which, like most other plants, need an inch of water a week.

Q. We have fungus gnats in the indoor plants that need to be kept outside in the summer. I have tried Neem oil but can’t seem to get rid of them.

N.A., Milton

A. Fungus gnats are actually small flies, about ⅛ inch long. They are drawn to moist potting soil and decaying plant material. While they look similar to mosquitoes, they don’t bite. Fungus gnats lay eggs in the houseplant soil. These hatch into larvae around a ¼ inch long with a shiny black head and an elongated, whitish body. They will sometimes eat plant roots, causing wilting. While it may be tempting to spray the adult fungus gnat, more adults will appear from the larvae already in the soil. So instead, let the soil dry out between regular watering and drain any excess water in saucers. You can also try Gnat Stix to trap the adults. Before bringing your plants inside in September, check that they are free of insects. A slimy trail on leaves can indicate gnats. Use a sterile potting mix when repotting.


Q. I have raised garden beds (12 inches deep) that do quite well, but I noticed that I don’t have any earthworms in them. I add compost (commercial versions) every spring, although this past year I added it in the fall without mixing it in on your advice. Should I buy worms and introduce them to my garden beds? If so, what kind of worms? Where do I get them? When do I add them? Do I need to do anything special to sustain them?

W.K., Yarmouth Port

A. I would just dig up a few “wild’’ (and free!) earthworms from the rich natural soil in your yard and deposit them in your raised bed to mate. Don’t buy worms online for your garden because many kinds of worms are foreign species. We all know that earthworms are good for gardens, but scientists are finding they are potentially not so good for northern woodlands and wild environments where they did not evolve. So stick with the worms that are already in your yard so you won’t risk introducing new ecological problems to your area.


From Aug. 16-25, the 152d annual Marshfield Fair (140 Main St.) will feature a flower show called “South Shore Summah,’’ presented by the South Shore District of the Garden Club Federation of Massachusetts Inc. and the Marshfield Agricultural and Horticultural Society. Call 781-834-6629 for information or visit Admission $12. Parking on the grounds is $5.

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