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Digging In: Scott Aker

When Flowers Lose Their Power

By Scott Aker
Special to The Washington Post
Thursday, April 14, 2005; Page H09

Q We moved into a new home two and a half years ago and planted a garden on the side, facing east. Although the garden gets some morning sun, nothing seems to flower here. We have hydrangeas that get very leafy and full, but no blooms since the first year. Other non-performers include a viburnum and astilbes.

Is this a soil issue or not enough sun?

A It may be a lack of light. Viburnum and astilbe will bloom if they have very light shade all day or at least a few hours of intense light. If there are trees to the south and east of where you have planted them, the plants may not be getting the full intensity of light that they need at their brightest period of the day.

A hydrangea can bloom in surprisingly little light, but it doesn't produce as many flowers and they tend not to be as large as they are in full sun. Some hydrangeas really require full sun. Any of the Hydrangea paniculata cultivars need full sun to reach their full potential. Florist hydrangeas and oakleaf hydrangeas can tolerate a lot more shade, but they won't bloom if they are pruned heavily in winter, since the flowers are in the terminal buds that are removed when you prune them.

I have planted tomatoes in the same plot for seven or eight years. Each year I turn the soil and bury pine needles, leaves and vegetable waste from the kitchen. There is no room to rotate my crop of tomato plants. Should I be doing more to replenish the plot? Would lime help?

A gardener doesn't rotate crops to build soil, but to prevent the buildup of pests and diseases linked to a specific plant or plant clan.

The organic matter that you are incorporating every year is feeding the soil as it breaks down. If you haven't seen a reduction in yields due to all the blights and wilts that tomatoes are prone to, simply continue with the practices that you have established. If you find that diseases are a problem, you may need to give tomatoes a break for a few years. This will also mean a rest for other edible members of the nightshade family, such as potatoes, eggplant, peppers, ground cherries and tomatillos. You can leave the plot fallow or plant a cover crop of soybeans or rye, or grow vegetables of different bloodlines. Generally, two to four years is long enough a hiatus to reduce the disease buildup.

In August I noticed what seemed to be white mites coming out of the mulch and flying everywhere. They were especially prevalent on my weeping cherry tree. I sprayed my plants and have tried to rake up the old mulch and dispose of it, but I am worried I will have a terrible infestation this year. What can I do to eliminate this problem?

I suspect you noticed an insect named a woolly planthopper, and it has nothing to do with the mulch.

Planthoppers are in the same group of insects as scale insects and aphids, and like them, they take their nourishment by sucking sap from plants. Unlike aphids and scale insects, they have the ability to hop away when disturbed. They also excrete strands of woolly wax, particularly when they congregate on a host plant. The waxy mess confuses predators.

Planthoppers feed on a wide variety of plants, and I have seen large numbers of them on flowering dogwood and flowering cherries.

Woolly planthoppers are often first noted during the dog days of summer, when they can be seen bumbling through the air. If you catch one, you will note that they are prone to hop around and already have a tuft of waxy filaments on their body. Gardeners often confuse them with mealybugs, which are far more damaging and harder to control. Woolly planthoppers do very little damage to plants and you needn't worry about trying to control them.

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

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