I MUST HAVE ABOUT 100 HOUSEPLANTS WHICH I HAVE BEEN GROWING FOR MANY YEARS. MY PROBLEM IS THAT THERE ARE THESE BLACK TINY KNAT TYPE PESTS WHICH ARE ALWAYS SWARMING AROUND THE PLANTS AND THROUGHOUT MY HOUSE. 2 TEARS AGO, THERE WERE SO MANY KNATS AROUND MY HOUSE , I TRIED MANY PLANT PESTICIDES, BUT THIS ONLY SEEMS TO KEEP IT UNDER CONTROL TO A POINT, BUT DOES NOT TOTALLY GET RID OF THEM. MY HUSBAND WANTS TO THROW OUT EVERY PLANT IN THE HOUSE, I HAVE HAD SOME OF THESE PLANTS FOR 30 YEARS. PLEASE TELL ME WHAT I CAN DO TO GET RID OF THE KNATS FOR GOOD. THX FOR YOUR HELP.
Please take this as a constructive advice. Using all caps is viewed by most people as the equivalent of shouting. It is best to use it very discreetly.
The presence of fungus gnats is a sure sign of unnecessary repotting, using contaminated soil, and not allowing plants to dry out sufficiently between waterings. Miracle-Gro potting mixes are notorious for harboring gnat larvae. A mix a 4 parts peat moss and one part perlite will serve you better.
More importantly, it is best to avoid repotting whenever possible. I say this because unnecessary repotting is the single most common cause of plant failure because it so often leads to inadvertent over watering and root rot. I have written a detailed article on proper repotting that explains all of this. I will email it for free to you (or anyone else) who emails a request to me at wcreed@HorticulturalHelp.com.
You have a serious gnat problem that will be difficult to get under control. It will take time and patience, but it can be done. Remove all loose soil that was added to the top of the rootballs and discard that loose soil. Many of the gnat larvae live in the top portion of the soil so discarding that extraneous soil will eliminate many of the larvae.
As the larvae mature by feeding on decaying roots they develop wings and then fly out of the soil. These winged adults will try to plant eggs in other plants that have damp soil on the surface. However, the adults will die in about a week of natural causes. So the key is to eradicate the larvae while allowing the adults to die on their own.
After removing the excess soil, you must cut back on your watering by allowing all of your plants to dry out to the point where they are ready to wilt. This is much drier than you think. Allowing the soil to dry will deprive the larvae of the moisture they require to survive. This will also help prevent roots from rotting and plants from deteriorating.
As I cautioned earlier, it will take several months to get rid of the gnats, although you should see a gradual decline in the gnat population well before then. Be patient and discuss this with your husband so he knows that to expect.
I have also written an article on treating indoor plant pests that I will email for free to you (or anyone else) who emails a request to me at wcreed@HorticulturalHelp.com.
Please let me know if any of this is unclear or if you have any additional questions.
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Will Creed, Interior Landscaper
Horticultural Help, NYC
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