Question
  I have two more questions regarding my house plants.  One, what is the best way to get rid of those little black gnats that seem to thrive on my plants' potting soil?  

  Second, I have a Peace Lily that hasn't bloomed at all this year and I was wondering what I could do to correct this problem.  

Answer
Hi Sandra,

Adult fungus gnats fly around and are an annoyance, but they are not harmful to people. Each gnat lives for about 5 days. The trick is to get rid of the next generation - the gnat larvae that live in the top layer of the soil. The larvae feed on decaying organic matter. Decaying pine bark in potting mixes and decaying plants roots feed the larvae.

Try to keep the soil as dry as possible. Remove all loose soil from the surface and put a light layer of coarse coir (coconut husk) or sand or diatomaceous earth on the soil surface. These substances have sharp edges that carve up the larvae. (Recent studies indicate that fine-textured peat moss also deters gnat larvae.)

Another safe technique is to place ?inch slices of raw potato on the surface of the soil. After a day or so, discard the slices along with the larvae inside. Repeat this until there are no more larvae in the potato.

For more serious infestations try Knock-Out Gnats to treat fungus gnats available from Gardens Alive for about $20. See http://www.gardensalive.com/item_display.asp?ProductNumber=1962

Detection trick: Add a little water to the soil and then look very closely for tiny fungus gnat larvae swimming in the water as it pools on the surface. You need good light and good eyes to see them. If you don't, then your plant is probably gnat free.

Prevention is often the best remedy. Use sterile potting mixes that are free of bark chips. The potting mix should have ample drainage material, such as perlite so that it drains well and allows the soil to dry out frequently. Fungus gnats can nearly always be traced back to overwatering and/or poor soil quality.

Spathiphyllum or peace lily is a sporadic bloomer and flowering varies widely with the particular variety that you have. Most will bloom once or twice per year, but never as prolifically as their original greenhouse-induced flowers.

Although peace lilies will survive in low light, they should be in bright indirect light to flower. Right in front of a north or east facing window that is unobstructed throughout the day is best.

Peace lilies flower best when they are quite potbound, so I advise against repotting. If you did repot yours, then that may be the reason it has not flowered.

The addition of plant food at half strength monthly will sometimes help promote flowers, but don't overdo it.

In sum, peace lily flowering depends on varietal genes, lots of bright light, a potbound condition, proper watering, and occasional plant food.

Please let me know if any of this is unclear or if you have any additional questions.

Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

You can E-mail me directly at: [email protected]

If this information has been helpful, please remember to give me an AllExperts rating and nomination.