Advice on Planting, Pruning and Picking Up

Q: Our oak trees have been dropping enormous quantities of acorns for weeks. In addition, they are shedding masses of tiny granular objects. Some sidewalks look like they're covered in sand. Can you tell me what it is? -- Ursula

A: The oaks might be shedding acorns because of the exceptionally long drought. Perhaps they didn't ripen well. Some rotted and fell; some are being eaten or buried by squirrels.

The "sand" could be from an infestation of oak lace bugs. Look closely and you will see minute, rounded, black or tan pellets. The nymphs hatch and feed on the underside of the leaf by sucking nutrients from it. The 1/8 -inch-long winged adults feed the same way. Pellets are droplets of waste from each insect.

Look at oak leaves on the ground. You can see tan and dark brown specks stuck to the underside of leaves. Verify the diagnosis with a licensed pesticide applicator, and discuss appropriate treatment.

Another possible issue is an insect called obscure scale. Some sloughed off the tree with the leaves. Scale forms about a 1/8 -inch-thick waxy covering that makes it tough to control.

Finally, wildlife is causing some of the debris. Squirrels eat bark and leaves and collect nuts for storage. Raccoons, which also like acorns, knock down a lot of nuts while climbing and feeding.

I would like to plant a fig tree or two that would produce lots of figs. Which variety would do best in Northern Virginia's clay soil and chilly winters? What are its requirements for sun and shelter? -- Susan

The most dependable fig for this region is Brown Turkey ( Ficus carica"Brown Turkey"). It needs moist, well-drained soil and full sun with protection from freezing in winter. A sunny southeastern wall of the house would be ideal. Planted about 18 inches from the wall, it is easy to make into an informal espalier, trained as a vine. Plant it six feet away if you want a shrub or small tree. Its mature size is 10 to 15 feet.

Plant with one part compost to two parts of your clay. Virginia clay is rich in nutrients, but it needs compost to help the fine particles release their "natural fertilizer." Plant fig trees in the spring, and don't let them go completely dry, as was easy to do this summer.

What is your opinion regarding the addition of plants in the nightshade family into a compost pile? -- Mary Lou

Plants in the nightshade family, such as tomatoes, peppers, potatoes and eggplants, are susceptible to viral and fungal infections that aren't always killed by composting. Even those infections that can be controlled must be subjected to high temperatures (150 degrees Fahrenheit) and remain hot for some time, while the pile continues to be turned, keeping it moist and mixing the sides into the middle almost daily to ensure good heat distribution.

Instead, when plants in this family freeze or stop producing, put them into the trash to help prevent the spread of disease next season. Also, choose plants that are bred to be resistant to as many of these diseases as possible. Codes on the seed packet or plant label will provide this information. Several key designations to look for are A (alternaria), ANTH (anthracnose), ALS (angular leaf spot), DM (downy mildew), F1 or F2 (fusarium wilt), PM (powdery mildew), T or TMV (tobacco mosaic virus)m and V (verticillium wilt).

I would like to try small volcanic rock mulch in my beds. What material should I put under it that won't shred easily? -- Brooke

I prefer a fabric barrier between soil and volcanic rock or other aggregate mulch. It helps control weeds and holds on to moisture. Pick a strong fabric, such as DeWitt Weed Barrier Pro, that you could use to lift the rocks if you decide to remove them.

Is it a good idea to rototill sand into clay soil? My yard has a layer of soil only three or four inches deep. Under that, it looks like solid clay. I will be tilling in compost and could till in sand, as well. Should I add sand or small pea gravel to the clay? Do you have any suggestions for organic matter than can be obtained locally? -- Woody

Organic material is the toughest substance to keep in the soil; it's also the most beneficial for improving drainage and adding nutrients.

Some plants, such as alpine plants that are adapted to exceptionally well-drained soil, will benefit from a finely -crushed gravel amendment. Spruce, fir, rhododendron, mountain laurel, heath and heather are examples. Other plants, such as oak, sycamore, river birch, sweet bay magnolia and winterberry holly, prefer heavy clay soil.

You can get ground leaves from your county or other municipality. The leaf mold might not be well aged at this point, but it can decay on the site where it is rototilled into soil.

Add about one part organic material to two parts native soil. Till to a depth of eight to 12 inches when soil is lightly moist.

We have a holly in front of our kitchen window that is at least 20 years old. It's about 10 feet tall. It will eventually block the view from the kitchen. Can we prune it so it will not grow taller? When is the best time to do so? -- James

I will assume it is a broadleaf holly, the type that has some thorns on the leaves. It can be pruned at the end of winter before growth begins. Cut it back from one-third to half its height by selectively cutting branches back to a crossing stem and lowering the shrub one branch at a time, while shaping it, until you have achieved the desired height. There should still be some greenery in the lower part of the plant, but it will be much more open. When growth begins in spring, the holly will renew at the new height and grow new foliage by August. If it is still not low enough, you can do another renewal pruning the next winter. During the coming years, touch up the plant as needed by pruning it in late winter.

I live in a condominium, on the fifth floor facing south. My balcony gets sun all day. I have a Bloodgood Japanese maple in a large container on my balcony. Despite daily watering and regular fertilizing, the leaves had brown edges all summer, and the plant is not thriving. What evergreen care do you recommend for a container? -- Jennifer

Japanese maples will commonly show heat stress in direct hot sun all day. Put it in a shadier location, and it should thrive. An evergreen that will take baking all day, provided you keep it moist, is American arborvitae ( Thuja occidentalis). Considered hardy to USDA Zone 2, it should stand up to summer and winter and can be pruned to any shape and size. Prune the roots when the plant becomes pot-bound in four to five years.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, http://www.gardenlerner.com.