Answer: Do not continue to use herbicide on the part of a lawn where bulbs are naturalized. Also keep in mind that wherever bulbs grow, the lawn cannot be mowed until the bulb foliage has died down naturally, which is usually late June for crocus.

        Q: Two years ago I planted Monarda didyma “Croftway Pink.” It took hold and grew well the second year, but disappeared the third. What is going on?

        A: Bee balm thrives in full sun to partial shade in any kind of soil. Because it spreads rapidly by underground runners, you should space plants — when initially set out — at least 2 feet apart. When grown in one spot for two or three years, bee balm often becomes weak, their centers bare. Dig up weakened clumps in early fall and replant young, rooted shoots taken from the outer edges.

        Q: About five years ago, my well-established Lirope plantings started to develop brown leaf tips in the fall. The plants don't die but are unsightly. What is the cause, and is there a cure?

        A: Brown leaf tips suggest a problem in the root area, often due to dry soil. The shallow roots of Lirope demand conscientious watering during long, hot summers. Use a slow, soaker-hose method and water to a depth of 6 inches. During a drought period, water weekly.

        Q: What can I do about an infestation of bagworms in my trees?

        A: The bacterial insecticide called Bacillus thuringiensis is an effective non-chemical control for bagworms. Read and follow directions on the label. Recommended chemical controls include diazinon or malathion (follow dilution and safety precautions on the label exactly). If you can puncture the nest (use a stick or pole), a spray will penetrate better.

        Q: The large conifers in my yard — red and white pines, American arborvitae, Norway and Colorado spruce — are underplanted with Baltic ivy and Virginia creeper. The vines have made their way up the trees to a considerable height. Will they hurt the trees?

        A: Some horticulturists believe that woody vines can kill trees by strangling or smothering them. Bittersweet (Celastrus scandens) is capable of this. The loose growing Virginia creeper and the straight-growing Baltic ivy do not strangle, although there is a remote danger that a small tree might be smothered by excessive shading out if these vines are vigorously growing and heavily leaved.

        Q: Is it true that perennials such as daylilies and coneflowers will choke underplanted bulbs such as daffodils?

        A: It's possible — especially with the thickly matted roots of daylilies. But choking is not the main problem here. When it's time to lift and divide either the perennials or the underlying bulbs, it's difficult, if not next to impossible, to work with one without damaging the other. You can avoid this problem by using good spacing between perennials and spring bulbs.

       Contact Tim Morehouse by Web site: www.getmoregarden.com; mail: c/o Cincinnati Enquirer. (If writing, enclose a self-addressed, stamped envelope.)

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