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Garden Plot: This is the year to get your lawn off drugs

Friday - 1/27/2012, 7:59am  ET

Fungus Gnats: Annoying houseplant pests

Johnny in Montgomery County writes: "Like most gardeners I have a collection of house plants. This year the fungus gnats have taken over so bad I'm at the point of throwing the plants away. The local garden center recommended some insecticide that I couldn't pronounce and I go by the rule of thumb that if I can't pronounce it, it will kill me, too, so I opted out of that option. Do you have a recipe for controlling these pesky little buggers? It wouldn't be so bad if they weren't in my face all the time."

Ha! They just like you, John.

Seriously, this is the prime time of year for these pests, and one way to start getting the nuisances under control is to get into the habit of under watering your plants. Many folks have a heavy hand with the water, and sopping wet soil provides the perfect breeding ground for these creatures. Allow your plants to dry out between waterings and you'll soon see fewer fliers. The nasty little larva can't survive in dry soil.

You can also end the cycle pretty quickly by preventing the adults from getting to that soil. After the adults mate, they lay their eggs in the soil of your house plants, where those eggs hatch into creepy little underground maggots. Spread an inch of sand on top of the soil or cover it with river rocks or shaped pieces of cardboard so the adults can't get through to lay those eggs, and the cycle will be broken.

And finally, watering your plants with the organic larvacide bacillus thuringiensis -- the same natural stuff that's in those "mosquito dunks" you use to treat standing water in the summer -- will kill the little maggots before they can emerge as flying adults. You should find it for sale at larger garden centers and Gardens Alive sells it online.

Pruning roses

Vince writes: "I'm president of the Men's Garden Club here in Frederick and we're going to assist a local garden by helping to prune their knockout roses. The timing suggestions I found for rose pruning online are confusing. Some sources say late winter or early spring, others April and some late summer. We ask for your expertise."

My pleasure, Vince, and thank you and your boys for your service!

Anyway, whoever said late summer is a big dummy. That would be the worst time to prune roses. Pruning in late summer or fall greatly increases a plant's risk of winter injury.

The perfect time to cut roses back is about two weeks after their new growth resumes in the spring. You can easily tell which branches are dead by then, and the plants have a lot of energy at that time of year for fast regrowth and self-healing of the pruning cuts.

You boys probably know what to do -- remove any dead, damaged or diseased canes, and open up the centers of the plants to insure good airflow. When you're done, be sure to remove all of your prunings and any old mulch that was under the plants. Then spread an inch of compost around each plant to provide a gentle feeding and a barrier against disease. Whatever you do, don't use wood mulch or shredded bark under roses -- it's a disease breeder.

Pruning fruit frees

John, just south of Fredericksburg, writes: "I'm confused as to exactly when I should prune my fruit trees. The past two years I've pruned my peaches and apples right after the dead of winter. But we only seem to have had a day or two of ‘dead winter', and I'm concerned that they might not have gone fully dormant. Is that concern warranted? And what about timing? I want to get it right, or at least not horribly wrong."

Don't worry about dormancy, John. Plants go dormant in response to cues like shortening hours of daylight and cooler nights. They don't need continued periods of freezing cold to get a good winter's rest.

And your timing -- pruning at the end of winter -- is sound. But you might want to wait a bit longer until the trees are in full flower. Then you can enjoy all of the blooms—and easily see where any dead branches are. The trees are also growing like gangbusters at that time of year and their pruning wounds heal fast—and that limits the amount of time that pathogens have to try to get in there and cause trouble.

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