Growing Concerns: Beware an Invasion of the Garden Snatchers

An article in a recent issue of a well-respected national garden magazine advises planting sweet cicely (Myrrhis odorata) to cover the flopping foliage of spent daffodils. I was shocked to read this. Yes, the herb’s ferny foliage is attractive. But what the article didn’t say is that sweet cicely has a dark side. There isn’t anything sweet about a ruthless invader that left unchecked, not only smothers bulb foliage, but can swallow up the perennial bed, the vegetable patch and the family dog.

Upon closer reading, I realized that the article directed this advice to gardeners in the Northeastern states. I assume that those infamous New England winters put a climatic leash on sweet cicely, whereas the relatively mild maritime winters of the Pacific Northwest allow the herb to easily reproduce and romp freely through our gardens.

There’s probably not a gardener alive who hasn’t experienced a problem with invasive vegetation. We’re not talking weeds here, either; rather, those attractive plants that we actually spend money to acquire. Johnny Jump-Ups jump up everywhere. English daisy, California poppy, sweet woodruff, Ajuga, Calendula, may go wild when no one is looking.

All potentially invasive garden plants are too numerous to mention here, but those loosely classified as herbs seem to head the list. There’s mint, notorious for hostile takeovers of moist areas. Valerian, bee balm, feverfew, oregano, dill and chives are also potential encroachers.

Among trees, rhizomatous (running root) bamboo can make a jungle of your garden unless grown in very strong containers such as armored vehicles or out-of-service navy destroyers. (Clumping bamboo varieties are much easier to control). Some locust trees can get out of hand, their seedlings springing up in unexpected places. English holly has become a Northwest nuisance, rapidly displacing native understory plants. English ivy is an insidious tree strangler; I’ll write more about it in a future column. Our native red alder is often considered a weed tree. Then there’s sumac, with its glorious fall coloration. Like potato chips, bet you can’t have just one! All these plants have their good points, but need to be controlled.

Speaking of glorious coloration, there’s the low-growing perennial, Houttuynia cordata. Attracted by its beauty, I took one to the counter of a local nursery, where the proprietor graciously informed me of its aggressive habits. I appreciated his honesty, and contained Houttuynia’s flamboyance in a flowerpot. On the other hand, I recently purchased bishop’s weed at a local plant sale. The name should have been a hint. Fortunately, I looked it up on the Web before planting, and learned that it could run rampant in my garden for years to come. I feel that if someone is going to sell a potentially invasive plant, that information should be provided to the buyer, either printed on the little plastic stake, or by the seller in person.

To be fair, climate, growing conditions and watchful gardening have a major effect on what’s going to be nice or nuisance. But to avoid the aggravation and hard work of ousting the invaders, even the most experienced gardeners need to educate themselves about the habits of the plants they purchase before planting.

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