Q. Can you eat the tuber from ornamental sweet potato vines such as 'Blackie' or 'Marguerite'?

A. 'Marguerite,' 'Blackie,' 'Sweet Caroline,' and others are ornamental cultivars of Ipomoea batatas, the familiar edible sweet potato. These ornamental varieties have been selected for their colorful foliage rather than their nutritional value or flavor. Their tubers are reportedly bitter tasting and not considered edible, although there is nothing toxic about them.

Q. I am fond of the shrub leucothoe, but mine are so marred by leaf spots that they are not as pretty as they should be. Is there anything I can do, besides spraying?

A. There are two primary species of leucothoe that are common in cultivation: Leucothoe fontanesiana and Leucothoe axillaris. Both are known by the common name dog-hobble, and are native to the southeastern United States, from Virginia south into Florida. These broadleaved, evergreen shrubs bloom in spring with drooping clusters of white, urn-shaped flowers. They are attractive landscape plants when not disfigured by leaf spots, and seem to be deer resistant in many areas. The new growth may be light green, or have a pink or purple tinge that hardens off to a lustrous dark green through the summer. Leucothoe develops a purplish winter foliage color that is quite attractive. L. fontanesiana grows 3 to 6 feet tall with a similar spread; L. axillaris grows 2 to 4 feet tall with a similar spread.

There are a number of leaf spot diseases that impact leucothoe in our climate, but the most common is a fungus known to pathologists as Cylindrocladium. It causes both a leaf spot and a root-rot disease that eventually kills infected plants. I have read that L. axillaris is more resistant than L. fontanesiana, but there are reports of serious leaf spot problems on both species.

Leucothoe is very fastidious about its cultural requirements. It prefers a shaded location -- the high shade of mature trees is ideal -- with an evenly moist, yet well-drained soil that is slightly acidic and has good organic matter content. It is found in the shade along stream banks throughout the southern Appalachian Mountains.

If you cannot provide such a habitat, leucothoe is almost certain to suffer from leaf spots. It does not tolerate heavy, poorly drained clay soil, full sun, drought or road salt.

It is best to avoid overhead irrigation that keeps the foliage wet for long periods of time. Although you cannot keep it dry from rain or heavy dew, you do not have to add to the problem by wetting the foliage when you water. Use soaker hoses or drip irrigation, if possible. At least water by hand with a watering wand so that you can direct the water down onto the soil where it does the most good.

Good air circulation around the plants helps them dry off faster, too. It is also good to use an organic mulch such as shredded hardwood or bark over the roots, but only use an inch or two, and never allow it to make physical contact with the stems. Mulch helps maintain soil moisture, moderate soil temperature, and provides some weed control.