Expert: Darlene K. Kittle - 10/18/2005

Question
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Followup To
Question -

How much rubbing alcohol to how much water?  Thanks.  I try not to use pesticides because I have 4 housecats who chomp on the odd plant.  I grow oat grass in a pot for them and make sure nothing poisonous goes on that.  Appreciate your help.


I normally have excellet results with my houseplants after setting them outside on the balcony for the summer (Canadian weather).  I just brought them in and they have small black flies.  Tried Safer's insecticidal soap in the soil, with no luck.  These flies are hovering around the plants as well as in the soil.  Any suggestions?  Thank you.
Answer -
Renee,

They are fungus gnats and are there because your plants have been overwatered &/or the soil has too much peat moss and is holding water too long so the roots don't have a chance to breath carbon dioxide through the soil between waterings so the roots begin to rot just as though they are sitting in a swamp. The rotting roots attract the fungus gnats. Let the plants dry out more between waterings and the gnats will disappear. Next time you repot those plants go to your nearest garden center and buy a bag of perlite and a bag of horticultural charcoal. Mix 2 parts potting soil with 1 part perlite and 1/4 part of horticultural charcoal. That will make the soil more porous and hold more air so the roots will not rot and attract the fungus gnats.
You can also water the plant with rubbing alcohol. It will kill the flies on contact in the soil and will not hurt the roots. Then you have to follow the above instructions to keep the fungus gnats from recurring.
Good luck.

Darlene


Answer
Renee,

I would use at least 2 parts alcohol to 1 part water or just straight alcohol. Straight alcohol will evaporate fast and not add to your "too wet" problem.  Rubbing alcohol is already diluted when you buy it. Remember you have to let the plants dry out more between waterings to solve the problem. The alcohol is only a temporary fix.

More plants are killed by too much water than by too little.
Good luck.
Darlene