lilac (Syringa vulgaris) photo by Schoeband
Queries concerning an assortment of garden plagues were received via e-mail during the past month.
Q: We have a lilac bush that we purchased about a year and a half ago. The leaves are moldy, and it is not growing. All the leaves have fallen off. It has buds on it, but it has never bloomed. It’s sick! What is the proper care for a lilac bush? How often should it be watered? Do you have any tips or advice on how to grow a healthy lilac bush?
– Kathy and Edna Fry
A: The fact that your lilac leaves are moldy is a sign that your shrub is not getting enough sun and/or air circulation. Lilac shrubs are highly susceptible to powdery mildew fungus on their foliage when sunshine and air movement are lacking in their immediate environment or microclimate. Although lilac leaves will burn from hot afternoon sun, they require a fairly exposed location nevertheless, open to plenty of ambient light, in order to reach their full potential.
More often than not, it is a lack of winter chill that prevents or limits lilac flowering in the spring. Lilacs are the classic spring-flowering shrubs in New York and Chicago, but not in Los Angeles. Yet there are several species (including Chinese, Persian, Hungarian and common lilac varieties) that should bloom reliably enough in the San Fernando, Santa Clarita and Antelope valleys.
The fact that your lilac has not bloomed during its first year and a half in your garden is no cause for alarm. It can take flowering shrubs several years to adapt to specific soil and climate conditions. I have seen shrubs bloom little, if at all, during their first several years in the garden, only to explode in bloom one fine spring day.
Lilacs require well-drained soil and regular watering.
They are not drought-tolerant plants and should be soaked twice a week during the summer. They prefer an alkaline soil pH, consistent with the pH of most soils in our part of the country. Lilacs should be pruned as soon as they finish flowering, since flower buds that open in spring are formed during the previous year’s growing season. Lilacs are deciduous, so do not be concerned when they defoliate at this time of year.
For the best local lilac display, make sure to visit the Descanso Gardens, located in La Canada Flintridge, in late winter or early spring.
Q: In August of last year, I noticed the hibiscus in my front yard seemed to have a white fibrous mold on many of the leaves and, when disturbed, some very small white flies flew around it. I water-sprayed the leaves with partial amelioration. This year the infestation has spread to nearby magnolia trees and climbing jasmine. The infestation is too high (up to 15 feet) and too prevalent to make spraying a viable option. Do you have any experience with or advice concerning this problem?
– Jerry Fagin, Valley Village
A: If your whitefly infestation is severe, the only way to alleviate it is by radical pruning two or three times a year, followed by weekly spraying with a strong stream of water from a hose. Although some progress has been made against the whitefly by release of its natural insect predators (parasitic wasps) in selected areas of California, the whitefly has become an increasingly unpleasant resident of Valley gardens.
As you indicate, the whitefly has been found locally on plants that, up until this year, had not been bothered. Lately, it has been observed on saucer magnolia, liquidambar and fruitless mulberry trees. It is to be hoped that with wider releases of parasitic wasps, this plague will soon be brought under control.
Q: Is there any way to get rid of nutgrass?
– Frances Russell
A: The only sure way to rid yourself of nutgrass is to sell your property and move to another neighborhood. I have found no reliable chemical-free solutions to this problem. The best product available for combating nutgrass is Manage, a liquid potion manufactured by Monsanto. It has been effective at controlling nutgrass in both lawns and flower beds.
