By Pat Dray
The Garden Spot
Pat Dray
I’m often asked if a specific plant is an invasive plant or merely aggressive. The difference can be a bit confusing since it’s really a matter of definition. According to the US Department of Agriculture, an invasive plant is one that is non-native and able to establish on many sites, grows quickly and spreads to the point of disrupting plant communities or ecosystems.
Here’s the tricky point: what does non-native versus native mean and why should a gardener care?
A non-native plant is one that is introduced with human help (intentionally or not) to a new place or new type of habitat where it was not previously found. One example of this is kudzu – referred to as “the vine that ate the South” and considered the most invasive in the world. Kudzu is native to Japan and southeast China and was introduced here in 1876 as an ornamental due to its sweet-smelling blooms and sturdy vines. Unfortunately, it outcompetes everything, including fully-grown trees, by overgrowing and eliminating the sunlight that the original plants needed.
Here in Connecticut we see lots of oriental bittersweet, which was brought here in the 1860s and now runs rampant. Like kudzu, it will eventually take down a mature tree. As you can guess, the non-natives have no native opponents to keep them in check and eventually destroy the native habitats.
Native plants originally occur within a region as the result of natural processes and are adapted to local climate and soils. They have co-evolved with native insects and wildlife and are critical to ecosystem function. This is important because over many years the insects and wildlife have developed to feed on and reproduce in these native plants.
An example that many of us are familiar with is the symbiotic relationship between the monarch butterfly and milkweed. In their larval state, monarchs only eat milkweed. Once the butterfly hatches, it helps to pollinate the milkweed. Without the native milkweed there are no monarch butterflies.
Aggressive plants are opportunistic native plants that are able to take advantage of disturbance to the soil or existing vegetation to spread quickly and outcompete other plants on the disturbed site. One of my favorite aggressive plants is goldenrod – if managed appropriately, its bright gold flowers can brighten up a woodland border. Another plus is that the deer don’t eat it.
There are a number of control strategies for both invasive and aggressive plants. The first is to identify them and not purchase one unless you are willing to continually exercise one of the following controls. You can contain it by leaving it in pots, which you bury or plant near a sidewalk or other mechanical barriers. Or you can try human control: continually pull it and dig it, being sure to get all the roots or rhizomes.
There are also some efforts at biological control. For example UConn is currently doing a research project for control of purple loosestrife. They’ve found that two particular beetles, Galerucella calmariensis and Galerucella pusilla, will eat and control it. This is part of integrated pest management.
As a last resort, spot treat invasive or aggressive plants very carefully with targeted herbicides.
Pat Dray is a past president of the Garden Club of Orange and a master gardener.