Question
Hey Darlene!
 I have a few plants at work that I suspect I have over watered and now we have these little black gnats flying around. What I have done was make a dilute soap solution and spray thoroughly on the plants and soil the past five days, no improvement. Now I have read that I need to let the plants drain, spray or poor alcohol on soil and then let soil completely dry out prior to watering again. My big question with this is will the rubbing alcohol hurt the plants or roots in anyway? Do I poor or spray and is it just for the soil? Is it straight alcohol or dilute? I'm sure of the names of each of these plants, one group is an elephant ear group, there is a fern/bamboo type plant housed with two plants that have long leaves off a single stem one is solid dark green the other is two toned green. One of the other plants is a type of Creeping fig, green with white edges growing up iron, The hanging succulents have some bugs around them and as far as I can tell, the hanging Creeping figs are bug free. My hanging plants are in false bottom planters, I don't water those very often, when they are dry, and I don't water the succulents that much.

Lastly i have a Orchid at home and its long lost its flowers when it was time, I water it just about every ten days. I got it maybe 6mo ago and haven't repotted it yet, I just heard I should do that. My concern is that it lost a large leaf at the bottom that started with a dark brown circle in the middle of it, then the entire leaf died and fell off, now the last two leaves look like they have brown circles in the middle of them as well?!?! what's happening!

Thank you for your time!
Desperate,
Jessica

Answer
Jessica,

#1, To prevent this from ever happening again never allow water to sit in the drain tray after watering your plants! This will cause root rot and that attracts the fungus gnats you are having now.

Straight 70% rubbing alcohol is already diluted. Diluting it more will just make your soil wetter and the goal is to dry out the soil as quickly as possible. It has never hurt the roots of any of my plants and it evaporates out of the soil in 24 hours. The roots of your plants are already damaged from the root rot from overwatering. We hope they are not too badly damaged already. This will kill insects and larva in the soil. It will not kill insects in the air. You do just pour it into the soil and use enough to get to all of the soil in the pot to effectively kill all the insects.  After using the alcohol empty the drain trays in all the plants an hour later. It would be good to leave them sit in the sink or tub for 24 hours without the drain tray. If they are so large you can't pick them up to empty the drain trays you can empty them with a turkey baster.

Never have your plants in a pot without a drain tray and good drainage holes. Self watering pots kill plants. When you repot plants always add extra perlite to the soil to provide better drainage and more air spaces in the soil so the plants roots can breath. Use a ratio of 2 parts soil to one part perlite.

As the plants dry out the insects in the air will disappear. Or you can use an aerosol insecticide or a bug bomb to get rid of them. Follow the instructions on the can.

As for the orchid the following website has excellent information: http://www.rv-orchidworks.com/orchids/orchid-care/orchid-pest-and-diseases/
After reading that if you suspect it is a virus or bacterial problem I would try spraying it with Lysol lightly holding the can at least 12 inches from the plant and enveloping it in spray. This has killed bacterial and viral infections on plants for me. Do it every 2 days for a month. Keep it separated from your other plants during this process. If the plant is still sick at the end of that spraying period pitch it, it is probably incurable at that point.

When you get a new plant study it and give it the care that it needs. Good luck.

Darlene