Q My fifth-floor condo balcony is enclosed and contains two window boxes. One has been planted successfully, but the lower box is a flop. The balcony is bright but doesn't get direct sunlight. Is there anything I can plant that would succeed, preferably something with flowers?
A If you want flowers, think begonias. A species named Begonia boliviensis has flowers more refined than the related tuberous begonias and is wonderful in any container or hanging basket where it can drape itself gracefully over the rim of the pot. The Angel Wing begonia is also easy to keep happy and is widely available in spring.
But don't discount foliage, especially in winter when the begonia may be between bloom cycles. I would suggest some ferns. I have been particularly impressed with Australian sword fern and a relative of the old standby Boston fern, the macho fern (Nephrolepis biserrata). It is much larger in every respect and the fronds are more leathery and darker green.
Try plants with colorful foliage such as Stromanthe sanguinea 'Triostar.' You can combine Triostar with variegated Hakone grass to stunning effect.
I live in an older Bethesda neighborhood where there are many pin oaks in the 35-to-45-year-old range. I planted two in my front yard in 1991. The older neighborhood trees are being marked by Montgomery County for removal, and my younger trees are dropping far too many leaves. The county tells me that pin oaks are suffering from a "bacterial leaf scald" and there is nothing that can be done to save them.
Should I just go ahead and cut my trees down now?
Bacterial leaf scorch is a disease that has been around for a long time that is getting more attention lately because of its prevalence in red oaks, scarlet oaks and pin oaks.
Trees may live for many years with infections and usually only die if faced with drought or some other stress. Symptoms are more pronounced in dry years.
Bacterial leaf scorch is caused by a bacterium called Xylella fastidiosa, transmitted to the trees by sap-sucking insects, usually leafhoppers. Once inside the vascular system of the tree, the bacteria multiply to the point of clogging leaf veins. This then causes leaf tissue to brown and die from a lack of water. Scorch is worse in drought conditions. It may also be more pronounced on a single branch or portion of a branch at first, often progressing to other branches or the entire tree.
Young trees from nurseries may be infected when you purchase them. The most frequent hosts are red, scarlet and pin oaks, and sycamores, American elms, sweet gums and mulberries.
There is no cure. Some arborists are willing to inject trees with an antibiotic. The symptoms usually go into remission for a time after the injection, but the disease is not eradicated, and treatment is expensive. Anything you can do to alleviate drought stress will slow the development of symptoms. If a single branch appears to be infected, removing it can slow or prevent the spread of the disease to other parts of the tree. If the symptoms are advanced, you may want to consider planting another tree that is resistant to bacterial leaf scorch, such as a white oak, willow oak, black gum or hickory.
Are there any weed killers that don't contaminate the soil?
Herbicidal soap is one option, and it works very well in situations where you have a carpet of new seedlings to contend with. Herbicidal soap is not very toxic and is largely ineffective against perennial weeds. However, it is very irritating to the skin and eyes, and should be used with caution.
Corn gluten meal works as a pre-emergent control for a variety of weeds. It is very expensive because you have to use a relatively large amount of the material for effectiveness. It also acts as a nutrient and supplies nitrogen and other elements as it breaks down. This may be a plus in some situations but is a detriment to plants that don't need extra nitrogen.
Scientists have studied using vinegar as a weed killer. Although it is quite effective against a variety of weeds, it only works when it is about twice as concentrated as household white vinegar. Like any acid at this concentration, it burns the skin on contact and its fumes may even pose a hazard to the lungs and eyes.
There is a theme here -- there may be some organic methods and products that may work on weeds, but they carry their own risks. The label will tell you the toxicity levels of various materials. Weigh the risks against the efficacy of the herbicide, regardless of whether it is natural or synthetic.
Scott Aker is a horticulturist at the U.S. National Arboretum.
Have a question about gardening? Write Digging In, Home Section, The Washington Post, 1150 15th St. NW, Washington, D.C. 20071; fax 202-334-5059 or e-mail home@washpost.com.
