Garden Q&A: Overwatering breeds fungus gnats
Question: I am having a problem with gnats in the dirt of my houseplants. My plants were fine until I brought a new one home from the nursery. They are not killing the plants, but quite the nuisance flying around my house. I've tried sprays, layering sand on top of the soil, removing an inch of the soil and replacing with diatomaceous earth, and completely replacing the soil with organic mix. My last attempt was to remove the plant from the soil and pour boiling water through the dirt hoping to kill the gnats and their eggs. I then covered the soil with plastic wrap for a week or so. I'm not sure if it has worked. Any suggestions? I enjoy having live plants in my home and would hate to go to artificial/silk.
Answer: When I was a kid, my older sister had a scrawny Norfolk pine in a mustard-colored, glazed ceramic pot sitting on a table in her bedroom. I never much cared for it. It wasn't the kitschy '70s container that made it unlikable, nor was it the plant itself. My distaste for that puny pine stemmed from the scores of little bugs plaguing it. Every time you walked past that pot, a cloud of tiny, black flies exited the soil surface. Inevitably one ended up in your nose … or eye … or hair.
I understand your frustration with this tiny insect.
Adult fungus gnats, like those in my sister's room and at your house, become problematic when their populations reach conspicuous levels, especially on houseplants. Individually, they are barely noticeable; by the hundreds, however, they are hard to miss. Their gregarious nature makes them a classic example of a nuisance pest.
Mature gnats measure a mere eighth of an inch and live for about a week. During this time, females lay eggs in soil fissures. The resulting translucent, minute larvae feed largely on the assorted fungi growing in the potting soil, though they also can feed on fine roots and plant debris. In a few weeks, they pupate into adults within the soil and the cycle continues, with several generations occurring together at any given time.
What my mother never seemed to figure out is that overwatering inevitably leads to a fungus gnat issue. Constantly damp soils promote fungal growth, which serves as an excellent food source for the larvae. Simply cutting down on watering should readily solve your problem.
Water infested houseplants deeply — but not frequently — and only when the soil is dry, even if that means only watering every two or three weeks. The life cycle of the gnats will be broken within a few months of reducing the frequency of watering. Be sure the pot itself has good drainage and the saucer underneath doesn't house standing water.
If changing your watering routine doesn't clear up the problem after a few months, re-pot all your house plants with new, sterile potting soil, gently removing as much of the old soil as possible without damaging the roots.
You also can trap adult fungus gnats on yellow or blue sticky cards placed an inch or two above the soil surface.
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 www.jessicawalliser.com.
Send your gardening or landscaping questions to firstname.lastname@example.org or The Good Earth, 503 Martindale St., 3rd Floor, D.L. Clark Building, Pittsburgh, PA 15212.
Show commenting policy
TribLive commenting policy
You are solely responsible for your comments and by using TribLive.com you agree to our Terms of Service.
We moderate comments. Our goal is to provide substantive commentary for a general readership. By screening submissions, we provide a space where readers can share intelligent and informed commentary that enhances the quality of our news and information.
While most comments will be posted if they are on-topic and not abusive, moderating decisions are subjective. We will make them as carefully and consistently as we can. Because of the volume of reader comments, we cannot review individual moderation decisions with readers.
We value thoughtful comments representing a range of views that make their point quickly and politely. We make an effort to protect discussions from repeated comments either by the same reader or different readers.
We follow the same standards for taste as the daily newspaper. A few things we won't tolerate: personal attacks, obscenity, vulgarity, profanity (including expletives and letters followed by dashes), commercial promotion, impersonations, incoherence, proselytizing and SHOUTING. Don't include URLs to Web sites.
We do not edit comments. They are either approved or deleted. We reserve the right to edit a comment that is quoted or excerpted in an article. In this case, we may fix spelling and punctuation.
We welcome strong opinions and criticism of our work, but we don't want comments to become bogged down with discussions of our policies and we will moderate accordingly.
We appreciate it when readers and people quoted in articles or blog posts point out errors of fact or emphasis and will investigate all assertions. But these suggestions should be sent via e-mail. To avoid distracting other readers, we won't publish comments that suggest a correction. Instead, corrections will be made in a blog post or in an article.
- Route 22 closed in Delmont after tractor-trailer crash at cloverleaf
- Starkey: Cervelli’s inspiration
- Vandergrift man accused of sexual assault
- More witness intimidation charges are filed against Plum teacher
- Downie, Ehrhoff lead list of likely Penguins leaving in free agency
- Supreme Court justices ream EPA for ignoring costs to meet air standards
- Pirates hope 1st baseman Alvarez starts to regain power stroke
- 80 percent of drivers found exceeding speed limit in Mt. Lebanon, Bethel Park
- St. Vincent professor, students use interviews for drug addiction data
- Wet weather puts Three Rivers Regatta events in jeopardy
- Pittsburgh Public Works supervisor disciplined for text message