A Tropical Option
QI noticed some interesting shrubs planted around the National Gallery of Art last summer. They are woody with deep-yellow bell- or trumpet-shaped blooms. A friend with horticultural knowledge identified them as Allamanda schottii, a tropical plant from Brazil. To me, the flowers look different. If it is this plant, can it be planted as far north as Washington? AThe
plants you noted are a different species, Allamanda cathartica. It has become fairly common in landscapes because it flowers profusely all season long and is quite tolerant of heat. It is technically a vine, but it seldom wanders much in our climate.
There has been a movement toward tropicals such as Allamanda in streetscapes and dooryard areas where bedding plants once prevailed. Tropicals take up more space than regular bedding plants, and thus it may be cost-effective, particularly when labor is figured in, to plant a few large tropical plants than to plant scores of bedding plants in a given area. Tropicals also sail through heat and bloom, even when confronted with the worst that summer can give them. Traditional bedding plants often take a break in midsummer.
Allamanda is not winter-hardy in our region, and in most of the country it is treated as an annual and replanted every year. It would need bright light and cool conditions indoors to survive the winter. We planted a tricolor beech tree three years ago. It is beautiful, and we love it, but now we realize it will get too big for our small property. Will it grow slowly enough to be all right, can we keep it down in size, or do we have to replace it with a smaller tree?
Tricolor beech grows exceedingly slowly, particularly in a hot site. Even in cooler conditions, it is not a large tree, growing to about 30 feet with a 20-foot spread after many years. Tricolor beech will manage only about six to eight inches of growth per year on average. You may have been looking at information relating to the species European beech, which can grow much larger, to 60 feet in height with a 40-foot spread. I have a patch of black mondo grass that has been dying back severely over the past two years. Is this normal, and will it rejuvenate?
The death may have been due to temperature extremes, drought or pests. Although it is perfectly hardy, mondo grass may respond to a sudden cold snap with the death of leaves, particularly the oldest of the leaves around the margins of individual crowns. Mondo grass can take heat, but it needs a consistent supply of moisture, and if the soil is allowed to become very dry, leaves may die back. This is more likely if the plant gets direct sunlight.
Another potential cause is fern scale, which you would find at the base of the leaves, particularly on the new growth. This pest can seriously stunt liriope and mondo grass. The presence of ants may signal scale because the ants farm the insects for their sugary excretion known as honeydew. Scale can be difficult to kill because they feed between leaves that are tightly packed in the crown of the plant. Cutting infested foliage as close to the crown as possible in spring and treating new growth with a pesticide containing acephate may help reduce the number of scale insects. If you don’t see new growth this spring, the plants are dead and should be replaced.
Scott Aker is a horticulturist at the U.S. National Arboretum.