Ground Covers Full of Grace

By Scott Aker
Special to The Washington Post
Thursday, September 18, 2008

Q Can you recommend any ground covers that I might grow in combination with existing Vinca minor. This is for a large bed, most of it in shade.

A Because vinca vines cover the ground, you should choose plants that are more upright. Whatever you select, you will have to cut the vinca away from other plants to prevent it from growing over them. To reduce maintenance on the vinca, plant the other plants in large masses.

Hakone grass is impressive for its adaptability. Consider a yellow variegated form such as Aureola or All Gold. Its graceful fountains of foliage would complement the dark green ground-hugging vinca. Some of the more ornamental woodland sedges, such as Carex siderostica, would fit the bill as well. Add sweet box for fragrance, and you will have created a successful ground cover garden with far more interest than a monotonous expanse of vinca.

I have a few tropical plants and herbs that I winter over in a greenhouse. In winter, they become infested by whiteflies and scale insects. This is particularly a problem on jasmine plants and a few herbs. Soap and oil treatments relieve the problem temporarily, but the pests return. What are possible treatments for jasmine and herbs that I will be eating?

Horticultural oil can be quite effective on both pests. The key is thorough coverage: Dip the entire plant in a bucket of the horticultural oil solution, mixed at a ratio of two to four tablespoons per gallon of water.

Late summer is a great time to remove all plants from the greenhouse and thoroughly clean the structure. A diluted bleach solution works well. When you put the plants back in the greenhouse, dip them in the oil solution first. If you spot mealybugs on any plants, dispose of them, since the bugs are nearly impossible to eradicate. If you move only clean plants back into your greenhouse, it is unlikely the problem will return. Be sure to vent the greenhouse well when you move the treated plants into it.

Horticultural oil can be used on edible herbs as well. If you are growing basil, parsley or other annual herbs, it might be best to start with new seedlings.

A year ago we had a large poplar tree removed from our side yard. It had been planted too close to the house, and the roots were going under the house foundation and tearing up sidewalks and patios. Now, the roots continue to advance, and little poplars are sprouting everywhere. What can we do to kill the roots and finally be rid of this home invader?

Treat the sprouts with an herbicide. Any herbicide containing triclopyr or glyphosate will work. Brush it on or apply it with a sponge to prevent any spray from drifting onto other plants. Use triclopyr if you must wait until after leaves have fallen to treat the sprouts.

Scott Aker is a horticulturist at the U.S. National Arboretum.

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