Plant Patrol: Nipping Space Hogs in the Bud

Keep out of the garden!

This warning might be meant for horseradish, mint, garlic chives and other incorrigible plants that can take over a garden. Unless these plants are watched carefully, the best place for them is a patch defended by a lawn mower or a semi-wild back corner of your yard.

With any of these unruly plants, choose the site carefully and keep an eye on them. All have assets to offset their bad behavior: the garlicky flavor and starry white flowers of garlic chives; the pungent, sinus-clearing flavor of horseradish; the yellow, buttonlike flowers and pungent aroma of tansy.

Horseradish is one of the worst offenders. Once this plant takes hold, it is almost impossible to remove from the garden. The most thorough digging will not remove every bit of root, and even the smallest bits of root will only resprout.

Try starving the roots out by repeatedly cutting off the leaves. New leaves keep pushing out, but three years of diligence might get rid of this plant.

Be careful even about throwing old horseradish pieces into the compost pile. Perhaps the traditional method for discarding quack grass should be applied to horseradish--pull it up, burn it, then spread the ashes where you are sure you’ll never want it to grow.

Garlic chive is another plant that can be frightening. One plant allowed to self-seed will be surrounded by hundreds the following year. This would not be so bad, except that the seedlings cling tightly to the soil, and the strap-like leaves are slippery and snap when you pull them--leaving the roots intact to resprout.

You could snip off the flower heads so seeds do not form, but most gardeners want to see the pretty flowers at least as much as they want to taste the garlicky flavor of the leaves.

Mint is almost as bad as horseradish. Whenever you see a sprig of mint poke up through the ground, rest assured that there is a foot-long underground stem pushing out from which will sprout new sprigs. The only way to rid an area of mint once it has established is by tracing the courses of these underground stems and combing them out of the soil.

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Horseradish, garlic cloves and mint are not the only unruly garden plants, of course.

Be especially wary of any plant that spreads where you can’t see--underground. Or any plant whose stems arch to the ground and root. Tansy and yarrow spread both ways. The way to keep these plants from spreading too far is to hack back their tops and chop back their roots every year.

Beware also of plants that, like garlic chives and horseradish, self-seed too readily or repeatedly sprout from root pieces. You need to plant dill and borage only once; from then on, your job each year is to remove excess self-sown plants rather than sow new plants.

These seedlings, unlike those of garlic chives, are easy to uproot--so with a little diligence they never get out of hand.

Jerusalem artichoke plants repeatedly sprout from even the smallest tubers left in the soil. But the plants just keep sprouting--not really spreading--so it rarely becomes as weedy as horseradish.