In the Garden:
Northern & Central Midwest
June, 2006
Regional Report

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This spearmint is lovely but it's an aggressive spreader.

Plants That Wander

I spent a few hours the other day pulling mint out of a garden bed. I intentionally put it in that spot several years ago, thinking the driveway provided a boundary on one side, and there was a field on the other side where the mint could spread without me having to worry about it.

Well, of course we changed our landscape, and now that area has new shrubs and a nicely mulched bed. So, I'm digging out the mint. This is the second time I've dug it out this year, and I know it won't be the last. At least it's quite pleasant work, with the sweet scent of spearmint wafting around me as I work.

Consider Invasive Tendencies
Plants that become invasive can be real problems in the garden, and my mint incident reminds me just how important it is to make good plant choices and good site choices. Many plants that become pests because of their invasive qualities are not native to our region, although there are certainly a few native plants that can escape cultivation and cause problems as well.

What exactly makes a plant invasive? Basically, a plant is considered invasive if it spreads prolifically by runners or seed and eventually begins to replace and dominate the existing plants. These plants can cause a change in local ecosystems in such a way as to harm the existing balance.

Plants like my mint or the phlox that delivers its undesirable seedlings all over the perennial garden are not necessarily invasive but simply weedy. I keep these plants in check by periodically rooting them out. Weedy plants are nuisances to the gardener, but don't threaten the environment.

Sometimes it can be hard to predict whether or not a particular plant species will become invasive in a new habitat. We've all heard of kudzu vines in the south, which were introduced into the country to stop soil erosion. The plants found happy homes, and are now literally bringing down southern forests.

As home gardeners, we have to rely on the plant breeders and scientists at horticultural institutions to do the research for us. However, we can do our part to keep these plants out of the landscape by only purchasing tried-and true-plants for our gardens.

It's our responsibility to be familiar with the plants that can become invasive because some invasive species are still sold in garden centers and nurseries. I certainly don't think anyone would intentionally plant garlic mustard or Canada thistle, but we do still find goutweed, euphorbia, dame's rocket, and purple loosestrife on the market for home gardens.

Some others to keep your eyes open for and avoid purchasing are moneywort, Japanese knotweed, reed canary grass (an ornamental grass), porcelain berry, Japanese honeysuckle, and even Norway maple and Siberian elm. There are extensive lists available through county Extension offices, so if in doubt, check it out.

As for those weedy plants in the garden, keep roguing out the seedlings and snipping off the runners. And if you want to plant something that does tend to run, put it in a spot where it's bound by sidewalks and driveways to keep it from heading off where you don't want it.


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