TX Organic Research Center



Are gnats hanging out on your houseplants? There's hope
October 28, 2009
By Howard Garrett


QUESTION: The gnats on our houseplants are driving us crazy. We repotted a number of plants this year to give them larger pots and used Miracle-Gro potting soil. Gnats later started living in the potting soil. We sprayed the soil and the plants with a pesticide, but the gnats are still there.

O.P., Dallas

ANSWER: I don't recommend potting soils that contain peat moss because they are expensive and they discourage beneficial soil microbes. I also don't recommend ingredients such as pine bark, perlite or concrete sand.  Potting soil brands that I suggest include Lady Bug, Nature's Guide, Rabbit Hill Farm, Soil Mender and Erath Earth. Ingredients you should look for in a potting soil include compost, coconut fiber (also called coir), expanded shale, lava sand, greensand, decomposed granite, alfalfa meal and beneficial microbes.

To get rid of gnats, soak the soil in the pots with my Fire Ant Mound Drench or a solution of neem oil. Mound drench concentrate is made of equal amounts of compost tea, orange oil and liquid molasses. Add 4 ounces of the concentrate to a gallon of water to create a solution to kill gnats. When using neem oil, follow label directions.


QUESTION: Bees are all around my koi pond, and I want to get rid of them. I don't know where the hives are, but what can I spray on the rocks that is not harmful to the fish?

S.H., Quitman

ANSWER: Orange oil will repel bees, and so will spinosad. However, both will kill bees if spray hits them.

Unless you are highly allergic to bees, however, the bees should be left alone. When foraging, bees are not aggressive. Bees also are beneficial and are critical for the pollination of flowers and crops.


QUESTION: We have neighbors who refuse to prune their overgrown photinias. The shrubs are 30 feet tall and almost reach the street in their front yard. These people told the homeowners association that the photinias would die if they are pruned at this time. Please confirm that pruning is good for shrubs and trees and especially for the neighborhood's appearance.

S.G., Dallas

ANSWER: Pruning is not necessarily good for plants. But if shrubs or trees are growing into other plants, blocking views or passageways or otherwise causing a problem, they can be pruned.  Minor trimming is better than major cutting, and the best time for pruning is late winter just before new growth begins. If shrubs are pruned now, new growth will occur at the wrong time of year or ugly cuts will be visible until next spring.


QUESTION: I've read that expanded shale and pine bark mulch are good amendments for improving clay soil. Where can I buy expanded shale?

G.L., Irving

ANSWER: Most garden centers that sell organic products stock expanded shale. Compost companies such as Living Earth (www.livingearth.net) and Silver Creek Materials Inc. (www.silvercreekmaterials.com) sell expanded shale in bulk. Shale is an excellent ingredient for soil improvement, but pine bark is not. Use compost instead of pine bark.


QUESTION: I bought my sister a gallon of Garrett Juice and a gallon of Medina Plus two or three years ago. She used a small amount of each liquid and stored the rest. She's ready to use them again, but are these products still good?

G.J., Tyler

ANSWER: They should be fine, but the liquids may have developed clumps of solids. Screen out the clumps before using the old liquids, or pour the liquids into a compost pile and then make or buy fresh Garrett Juice and Medina Plus to use in the garden.


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