IN THE GARDEN WHEN TO WORRY ABOUT EUCALYPTUS TREES.

Byline: JOSHUA SISKIN

Q: I have two eucalyptus trees about half an acre apart that were infested with lerp psyllids two to three years ago but seem to have recovered. Both have openings in their outer bark, one 3 inches above ground level and the other 3 feet above ground level. What is this, and is there any treatment? I'm afraid this will weaken the trees and they might fall over and hit someone. I have 11 other healthy eucalyptus trees.

- Penny Frisbey, Santa Clarita 

A: In a description of lerp psyllid damage from the Los Angeles Department of Recreation and Parks, it was reported that in addition to defoliation, the most common symptoms were splitting and peeling of bark shortly before dying. Before you take drastic measures to remove the trees, however, especially since they seem to have recovered, I would consult with an arborist. Eucalyptus trees are known for shedding their outer bark, only to reveal smooth patches of older bark below. Ascertain that your problem is related to psyllid damage, and not to normal sloughing off of bark, before pulling your trees.

The fact that most of your eucalyptus trees are healthy indicates that you probably have a variety of types since the lerp psyllid, a sap-sucking insect, locally attacks two species: red gum (Eucalyptus camaldulensis) and flooded or desert gum (Eucalyptus rudis).

Q: My friend turns his sprinkler system off entirely for the duration of the winter. I leave mine on, generally, but when it rains, or is forecast to rain, I turn it off, often for several days at a time, and usually wait until temperatures return to the 80s before resuming irrigation. Which one of us is right?

- Andy Roth, North Hills

A: This winter was warmer than most and it was necessary to water the lawn two or three times a week until the rain finally fell. However, if your neighbor's lawn faces north and yours faces south, for example, you would probably have to water more often because of greater sun exposure. You also need to factor in exposure to the wind, which can suck water out of lawn and plants regardless of temperature.

There are a number of other factors that contribute to a lawn's ability to survive with less water, starting with soil preparation. The amount of organic material used in preparing soil for planting a lawn can have long-term effects on water economy. The more amendments - compost, Nitrohumus, Gromulch - used prior to planting, the greater a lawn's ability, over time, to make do with less water. Even if you did not improve soil prior to planting, you can improve water retention by sprinkling a thin layer of compost or gypsum on the top every few months. Aeration is also helpful, as is application of wetting agents that make water stickier and soil more water retentive.

Q: Last fall, I separated and transplanted three Clivia miniata that a friend gave me. I planted them in front of a pine tree. They get morning sun, and are in the shade by about 11 a.m. But they aren't blooming. They do have a couple of new leaves in their centers, but the rest of the leaves look brown on the ends. Are they: Not acclimated to the soil yet? Too close to the tree and competing with the roots for water? Needing more or less sun?

- Susan Schless, Northridge

A: Kaffir lily (Clivia miniata) flowers with as little sun as any other perennial. Its flowers are usually orange, but yellow and white varieties are also available, accompanied by sea-green straps of foliage. Clivia is a slow grower, however, and acclimation following transplant could easily take a year or more. The fact that you have new growth in the center is a good sign, and I would not worry about burnt leaf tips. You should not worry about competition from pine tree roots since clivia roots, like those of all herbaceous or bulbous perennials, are shallow. Clivia growth will not be inhibited by the few hours of morning sun you receive.

TIP OF THE WEEK: The most beautiful plant that is flowering right now is Centradenia grandifolia, which grows up to about 3 feet tall even as it spills all over the place. This relative of the princess flower (Tibouchina) is virtually unnoticeable most of the year as it slouches around the garden. But just when you think it is only taking up space, it erupts in a bright magenta display. It requires no special attention, and you need only resist the temptation to pull it out, since it does sulk most of the year.