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Many people confuse the terms invasive and aggressive, or even use them interchangeably. An invasive plant is generally defined as a non-native plant that grows quickly, reproduces efficiently, and has no natural enemies to restrain its expansion. There are several species that are considered invasive by the Ohio Invasive Plants Council. Their website http://www.oipc.info/ is both helpful and informative in identifying these species.
On the other hand, an aggressive plant is one that may take over the area where you plant it, becoming an uncontrollable pest in the garden. Mint is a great example. People love to plant it because it’s lush, green and smells great. But it sends runners out under the soil that you can pull for days and never get it all. However, you don’t tend to see mint popping up in the woods, or crowding out native species. Aggressive plants may take over where you plant them, but they don’t usually seed freely into natural areas.
Listed below are plants that don’t necessarily qualify as invasive, but that you might want to think twice about including in your garden. That’s not meant to out right condemn these plants, but to make sure you plant it with care.
Iris pseudacorus, Yellow Flag Iris
Native to Europe, this iris does flourishes in wet areas, on the edges of streams or lakes, or in rain gardens. Beautiful yellow flowers make this plant appealing, but it grows and spreads quickly, taking on a more weedy habit. Listed as an invasive plant or noxious weed in several states, this iris can now be found throughout most of the United States and Canada.
Pycnanthemum sp., Mountain Mint
There are twenty one varieties of mountain mint, all native to the eastern half of the United States. Silvery leaves and white or pink flowers, mountain mints have been used as a culinary and medicinal herb. While it is a beautiful plant, if you decide to include it in your garden take great care in where you put it. It grows by sending out runners on and beneath the surface, quickly taking over a large area.
Mentha sp., Mint
The genus Mentha includes between 20-25 species, in a variety of scents, leaf shapes, sizes and flowers. But they all share the same growth characteristic of being aggressive growers in the garden. Like mountain mint, listed above, mint species grow via runners that travel on and beneath the surface. One plant can take over a large area, easily overtaking other desirable garden plants. While many gardeners choose to grow mints in containers, if you do find it growing in your beds, it’s always enjoyable to weed.
Running Bamboos (several genera)
There are several varieties of bamboo, including the non-aggressive clumping varieties and the more aggressive running varieties. The running varieties are frequently used for screening out unwanted views or neighbors, but gardeners beware. These plants can be very aggressive, sending runners underneath sidewalks and roadways; popping up in places you don’t want it. Once established, running bamboo is very difficult to eradicate. There is a native running variety that is slightly less aggressive, but given time can also become pushy and over-bearing.
Panicum virgatum ‘Prairie Sky’, Switchgrass
Usually a good team player, most cultivars of switchgrass make excellent choices for the home garden. ‘Prairie Sky’, however, has proven that it can seed readily into the surrounding landscape, making it a nuisance to weed and an unwanted intruder. Try Panicum virgatum ‘Northwind’ or ‘Shenandoah’ as replacements.
Houttuynia cordata ‘Chameleon’, Lizard Tail
Colorful foliage makes this plant an appealing choice for a groundcover, but be careful where you put it. Spreading from underground rhizomes, this plant forms a dense mat. Breaking the fleshy underground stems only encourages new growth, so pulling can be frustrating. It does exceptionally well in moist soils and might be more restrained in drier locations. Best used with boundaries, such as sidewalks, to prevent uncontrolled spread.
Petasites japonicus ‘Giganteus’, Japanese Butterbur
Flowers that push out in late winter followed by enormous, textured leaves make this a unique and interesting choice for the garden. The male and female flower parts are on different plants, so it can’t make seeds unless you have one of each. Probably just as well, since it’s prolific, almost to a fault. Watch out for the runners that allow this plant to spread rapidly through the garden.
Euonymus fortunei, Wintercreeper
Commonly used as a groundcover, this evergreen can also be grown as a vine or a mounding shrub. Unfortunately, not only is it an aggressive spreader in sun or shade, it also has a habit of turning up in new places thanks to the birds eating the fruit.
Hedera helix, English Ivy
Even weekend warriors can identify the three to five-lobed leaves of English Ivy. Like wintercreeper, ivy can be used as a ground cover or a vine and spreads aggressively to fill in empty spaces, like under trees. When growing horizontally, its only offense is that grows out of control rapidly and can be difficult to eradicate should you change your mind. When allowed to grow vertically on trees or walls however, the leaf shape will eventually become more rounded and the vine will begin to produce berries which the birds like to eat and disperse.
Physostegia virginiana, Obedient Plant
Don’t let the common name fool you, because this plant is anything but obedient. Beautiful and unique, but it doesn’t exactly stay where you put it. It’s called obedient plant because you can turn the flowers to face one direction or another. A neat party trick, to be sure. It does exceptionally well in moist soils, but can spread unchecked by underground rhizomes when it’s found a happy spot.
Euphorbia cyparissias ‘Fen’s Ruby’, Cypress Spurge
A beautiful groundcover with fine, blue-green leaves that start out red in the spring. It grows well in drier soils and forms a dense mat. Unfortunately, it can spread aggressively and be difficult to eradicate once established. Being a euphorbia, it releases a milky sap that can irritate the skin when you are weeding.
Aegopodium podagraria ‘Variegata’, Snow-On-The-Mountain, Bishop’s Weed
A variegated groundcover to brighten shady areas, this plant is commonly used when quick coverage is desired. It is tolerant of a variety of soil conditions and spreads readily via underground stolons. Best when used with boundaries, such as between the foundation and a sidewalk. To give an idea of its aggressive habit, I have seen this plant compete admirably with English Ivy.
Lysimachia nummularia ‘Aurea’, Golden Creeping Jenny
Often sold in garden centers as an annual, this plant is a beautiful addition in containers, draping brightly and gracefully over the side of the pot. However, it is hardy and can spread rapidly and aggressively in the garden. It grows best in moist, shady soils. Whether planted purposefully or allowed to reach the ground from the side of a container, one small piece of this plant can form a six foot golden mat by next year.
Ranunculus repens ‘Buttered Popcorn’, Creeping Buttercup
An attractive spreading groundcover with small yellow flowers. It is adaptable to sun or shade, but spreads more aggressively in moist, shady spots. Like all buttercups, this plant should be planted with caution.
Rhamnus cathartica, Common Buckthorn
Ranunculus ficari, Lesser Clendine
Polygonum, Japanese Fleece Flower
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