In the Garden:
New England
February, 2005
Regional Report

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Lovely as it is in fall, burning bush can invade natural areas because the prolific seeds are so tempting to birds who deposit them far and wide.

Plants That Don't Know Their Place

I was quite fond of the tall spikes of pinkish purple flowers that bloomed all summer in the garden of a house I had just moved into. I didn't know what they were, but I worked around them as I added new plants and dug up others. Then I started noticing these flowers all along the roadways and found out the reason they were such stalwarts. Those purple loosestrife (Lythrum salicaria) were one of the more invasive weeds in the entire United States.

Common Exotics
Loosestrife was most likely introduced into the U.S. from Europe in the 1800s, so it's called a "common exotic." The term sounds like an oxymoron (like "jumbo shrimp" or "working vacation") but it's actually a useful description. Horticulturists use the term "exotic" to describe nonnative plants, and these exotics can become common when they're popularized by plant breeders, or when they're so prolific their offspring turn up everywhere.

Exotics such as loosestrife can spread so far and fast they choke out other plants, threaten native species, and ultimately reduce biodiversity. Some of these plants may have no natural enemies (such as herbivores and insect pests) or they may be unpalatable to wildlife so there's little to keep their populations in check.

Even a native plant can become invasive if we alter its natural habitat enough and eliminate the species or conditions that used to keep it in check.

Some plants are bad actors wherever they grow; others are wickedly aggressive in some regions, while they know their place in other, less-hospitable climates. Purple loosestrife spreads naturally by floating seeds, so it's less of a threat in arid parts of the country. Similarly, the moonflowers that I try (not very successfully) to grow every summer are rampant weeds in hot climates.

Be Wary
It's easy to innocently bring plants into our gardens without realizing their potential to spread into nearby wild areas because a visit to the garden center can turn up numerous plants that are potentially invasive. Japanese barberry (Berberis thunbergii) and burning bush (Euonymus alatus), for example, tend to behave themselves in urban areas but spread easily into the wild when planted near woodlands and pastures. Birds devour the berries, and then fly away to deposit the undigested seeds, along with a little dollop of fertilizer for good measure.

Several maples, privets, and honeysuckles are on the Invasive Plant Atlas of New England, a list that includes 111 species. I was dismayed recently to read that butterfly bush (Buddleia davidii) also has rampant tendencies because of its prolific seed production. Some states are even banning them. But don't rip out your plants yet because Longwood Gardens in Kennett Square, PA, has been testing different varieties and has found that 'Orchid Beauty', 'Summer Rose', and the new B. weyeriana produce very few seeds. In addition, B. fallowiana, B. hemsleyana, B. longifolia, and B. nivea were found to be relatively low in seed production.

What To Do?
As with butterfly bush, some types of plants have invasive species and noninvasive ones. So, we do a little research and make smart choices. Or we grow questionable plants with a watchful eye and remove spent flowers, seedpods, volunteer seedlings, runners ... whatever it takes to keep them in bounds. This can be a lot of work.

With so many choices out there of wonderful plants, I'd rather spend my time enjoying the ones that are content to stick around than try to tame the ones that think the grass is greener on the other side of the fence!


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