Q: We have lots of rhodies (not sure of the variety, as we didn't plant them). Only one bush produces flowers, although they all bud as though they are trying to produce flowers. Someone told me to fertilize them and put compost around them, so I did that last fall, and still nothing this spring. Any thoughts?

A: The usual suspects when rhododendrons fail to bloom are dense shade, drought or overfertilization. Some sources also say rhodies need careful and thorough deadheading to bloom their best, although I've seen many rhododendrons in near-abandoned gardens that are never deadheaded, nor fertilized, and still bloom just fine.

While we think of rhodies as shade plants, they do need light and some sun to set bud and open flowers. Experts at Oregon State University recommend fertilizing with a 10-6-4 formula (more nitrogen than used to be suggested for rhodies), once in February or March before the plant blooms, and again after bloom in June or July.

Rhododendrons have suffered from drought in recent years, because they prefer to be constantly moist. In spring, the plants use large amounts of water for new growth and flowers. Since their evergreen leaves can create an umbrella that sheds the rain, the poor plant's rootball remains dry and the flowers suffer. If a plant hasn't received sufficient water, the buds might fall off without opening, which sounds like what might be happening to your rhodies.

So, water them regularly and thoroughly, paying special attention not only during summer drought but also in springtime; fertilize sparingly twice a year; top-dress with compost (but not too thickly, as rhododendrons have shallow root systems); make sure they're getting some sun, and your rhodies should bloom again next year.

Q: I separated my irises two years ago, and they haven't bloomed since. The green leaves get tall, but no blooms.

A: I consulted Brian Thompson, iris expert and librarian at the Miller Library at the Center for Urban Horticulture. He says your iris problem suggests the plants are receiving insufficient light, especially if the leaves are taller than normal (stretching for the light). But some iris varieties are just slow to reestablish. Also, while some early varieties already are in bloom, many later ones have yet to show buds but still should bloom this spring. For more help, Thompson recommends the King County Iris Society's bearded iris culture page at: www.kcis.org/kcisbeardedculture.htm.

Valerie Easton also writes about Plant Life in Sunday's Pacific Northwest Magazine. Write to her at P.O. Box 70, Seattle, WA 98111 or e-mail planttalk@seattletimes.com with your questions. Sorry, no personal replies.