How do you eliminate black bugs from plants brought indoors for the winter?

Answer 1

These black flying critters are called fungus gnats and pose a three part problem for you: adult, larvae and eggs. The adults like to lay their eggs in the moist soil of your houseplants and when they hatch the larvae eat the roots. The most non-toxic way of controlling these gnats is to eliminate the adults as they leave the soil and mature from larvae thus preventing them from returning to the soil to lay more eggs. You can use several different non-chemical methods if you have the patience.

I have done this by placing little saucers (I use jar lids) filled with distilled white vinegar around all the houseplants-don't be stingy. The adult gnats are attracted to the liquid and drown. This may take a week to get all the adults as they emerge from eggs and larvae already in the soil.

Another non-toxic method is to spread a minimum of 1/2 inch of sand on top of the soil of all the houseplants. This prevents adults from returning to the soil to lay eggs. Again this may take a week to be rid of all the gnats as their life cycle plays out.

Yellow sticky traps from almost any garden center (or internet order) are another method of catching the adults as they emerge and preventing more eggs from being laid.

Going easy on the water for your plant also should help control the problem. These gnats thrive in wet soil. If your plant can stand a little dry out this may be the easiest method for you. I have put an elephant ear plant infested with these gnats in my hot garage for about a week without water and brought it back in the house gnat free.

Some other methods I've read about but not tried include introducing beneficial nematodes to the soil and using a product called BTI.

Answer 2

It is by insecticidal soaps, manual removal, and water sprays that black bugs can be eliminated from plants brought indoors for the winter. It also may be helpful to repot the plants in the event that something which should not be in the soil is keeping the roots company.