Trailing Geraniums Dislike D.C. Heat

By Scott Aker
Special to The Washington Post
Thursday, July 2, 2009

Q In France and Israel I've seen beautiful trailing geraniums planted everywhere in window boxes and planters. They have red and white flowers and look like the common upright geraniums except that they trail. I would like to plant them but haven't been able to find them locally. Will they grow well here?

A You are referring to ivy geraniums. Balcon is the name of a series that is widely used in Europe for window boxes and hanging baskets.

They are not popular here because they do not thrive where summer night temperatures are much above 65 degrees. They may survive but are not likely to flower well during summer heat.

I suggest you try growing coral plant, Russelia equisetiformis, in window boxes. It thrives in heat and will be in full color during the hottest period of summer. Its wispy, grasslike foliage sets off the coral-red flowers very nicely, and it will continue to bloom until frost.

I planted a dark pink dogwood tree three years ago, and each year it has bloomed more than the year before -- until this year, when it had only two blooms. It gets sun until midafternoon and is in a small front yard. The soil is not great, but I mulch every year, and it hasn't been a problem before. The tree is thriving except for the lack of blooms. Is there anything I can do to encourage more blooms next year?

Plants are more complex than most people realize, and flowering is controlled by a host of factors acting on the plant at the same time. Dogwoods and other spring-flowering trees and shrubs begin to develop their buds the previous summer and fall. If the soil is too dry or wet at that point, the result can be sparse blooming. This is a common problem with dogwoods.

Also, powdery mildew may have compromised the tree's ability to make and store carbohydrates needed to produce flower buds. In addition, vigorous growth may compete against flower bud production. If you want a bumper crop of flowers, avoid fertilizing the tree, including on any turf that might be in the area shared with the tree's roots.

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

View all comments that have been posted about this article.

© 2009 The Washington Post Company