A closer look at compost tea

Q: My local nursery is selling compost tea, and the salesperson claims it will make my roses healthier. What do you think?

A: Compost tea is a hot-button topic among gardeners, some of whom swear by its near-miraculous results, while scientists question its worth. Linda Chalker-Scott, associate professor at Washington State University Puyallup Research and Extension Center, says master gardeners no longer sell nor recommend compost tea. Chalker-Scott puts compost tea under the heading "horticultural myths," and says scientific research fails to show its value.

I also checked with Bainbridge Island plant pathologist Olaf Ribeiro, who took part in a compost-tea panel at a recent meeting of the Washington Florist's Association. "Claims have been made that compost teas will suppress or control a wide variety of plant problems. Thus far I haven't seen any of this in the landscapes where compost teas have been applied," says Ribeiro. "The big drawback is that compost tea has to be applied frequently, so it's costly for homeowners."

Also, the teas need to be kept aerated, or you end up with more anaerobic than aerobic microorganisms in the brew. It needs to be applied as soon as possible after brewing for maximum microbial effect. "This is a short-lived product," concludes Ribeiro, adding that while the compost tea's long-term effect of adding microbes to the soil is beneficial, it can be done more inexpensively with aged manure or well-composted mulches.

A major concern with compost teas has been in the inconsistency of their make-up. This problem has been reduced by the use of commercially produced compost brewers, but Ribeiro says his clients who have purchased brewers have not seen much difference to justify the extra cost.

Many expert gardeners and landscape managers feel compost tea has clearly proven its worth by the results they've seen. But I have to say that many of the compost-tea proponents have a financial stake in the product, as opposed to the scientists quoted above. Common sense suggests that compost tea is an extra step in the process and one that is expensive with unproven results. Why not just apply compost and manure and let nature have its way with washing the nutrients down into the soil? This tried-and-true approach won't have such instant results, but improves the soil and feeds the plants over a longer time.

Q: I saw some boxwood cones in pots and am thinking about planting some small shrubs to make into topiary. Is this a bad idea?

A: If you like the look of topiary, it fits the style of your garden and you don't mind the work involved in shearing and shaping, then it isn't a bad idea. But Cass Turnbull, pruning diva, warns that "just because it's sheared doesn't mean it's topiary."

Turnbull defines topiary as a form of pruning art that breaks the rules of good pruning to create an effect, while not harming the plant's health. The trick to successful topiary is to choose the right kind of plant in the first place, which is one with lots of very small leaves growing close together. Ideal plants for topiary are tough enough to take repeated clipping, and they break bud soon after shearing, so fill back in quickly. The boxwood you admired, plus yew, privet and pyracantha, are all good bets for clipping, shearing and shaping.

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.