Q: I planted several staghorn sumacs on my back rockery a few years ago. They're really beautiful this fall but are sending up suckers everywhere. I'm afraid they'll swamp the smaller plants. I chose them because I'm trying to grow all natives in my backyard. How can I make the sumacs behave?

A: Beautiful as they are, I've never known a staghorn sumac (Rhus typhina) that came close to behaving in a garden. These big deciduous shrubs have finely dissected leaves, furry brown stems and cones, and brilliant red fall color.

Unfortunately, they're aggressive plants, ideal for the tough conditions in your rockery. They aren't, however, native to the Northwest, but hail from eastern North America.

It's the natural tendency of staghorn sumacs to form colonies by sending out rhizomes. Of course you can cut off and rip out the brittle rhizomes regularly to keep them (somewhat) under control.

Because it sounds like you admire your sumacs, it might be best just to let them colonize and take over your rockery. If this idea doesn't appeal, or if you want to try for a true native-plant palette, you should remove the sumacs before they really take over.

You can replace them with, perhaps, red flowering currant (Ribes sanguineum) and vine maples mixed with mahonia for winter interest.

To learn more about native-plant choices for difficult conditions, take a look at King County's native-plant guide (dnr.metrokc.gov) or visit the Washington Native Plant Society's Web site, www.wnps.org. If you prefer a book, there's Art Kruckeberg's classic "Gardening with Native Plants of the Pacific Northwest."

Q: Last summer I used a spray called TerraCycle on my container flowers, and they're still blooming in October. The guy at the Home Depot recommended it so highly that even though it was expensive I bought some. Do you think it really helps, or maybe it was the packaged soil I used? I hope to repeat this success next summer.

A: Wouldn't it be great if Home Depot and other big-box stores carried more organic products like TerraCycle so we could shop in their gardening aisles without feeling overwhelmed by poisonous fumes? It seems so wrong for gardening supplies to smell like chemical death, don't you think?

To answer your question, worm castings — or, as TerraCycle says, "worm poop" — is the secret ingredient in this new product. Packaged in recycled soda bottles, TerraCycle claims to have a negative environmental footprint.

It sure sounds easier to spray on some "black gold" than to take care of a worm bin in order to harvest your own.

That said, you might also want to repeat the watering regime you used this summer, as well as refresh your containers with more of the same kind of packaged soil. Fertilizer can bulk up annuals and keep them blooming, but they'll only look their best planted in good soil and watered regularly.

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.