Garden & Landscape Tips

What is an invasive plant?

An invasive plant meets these criteria:

  • Is not native to North America.
  • Spreads rapidly by roots or a large number of seeds that easily sprout.
  • Grows and matures quickly.
  • Tolerates of many types of growing conditions.
  • Is aggressive, especially in soil that has been disturbed, disrupting natural ecosystem.

The federal government, states and regions determine which plants are invasive and offer suggestions on controlling these species and recommendations for alternatives. What is invasive in Florida may not be in Texas or Missouri and invasive species in Massachusetts may not be troublesome in Wisconsin. To find out more about which plants are invasive in your community and what you can do, visit the Invasive Plant Atlas of the United States, or your state’s native plant society.

Here are some of the worst:

Garlic mustard

garlic mustard
Garlic mustard rosette
Photo courtesy Purdue University

Garlic mustard (Alliaria petiolata) was brought here by Europeans more than 100 years ago, grown for its namesake flavors in salads. However, this plant has escaped gardens and taken embedded itself in thousands of acres of natural areas, farmlands, alleyways and garden beds.

Garlic mustard is a biennial that spreads rapidly by seed. It thrives in full sun to full shade. The first year, rounded, serrated leaves form close to the ground, called a rosette. In year two, the rosette sends up a flower stalk and blooms white star like flowers. As seeds ripen, they are spread from the flowers by wind, animal fur and birds.

What to do? For best results, remove the rosettes from the landscape by pulling. They also can be treated with a weed killer, but make sure to read and follow the label directions on the product you use.

arugula
Arugula
Photo courtesy National Garden Bureau

Try to keep garlic mustard from flowering. Chop off the plant at ground level, and it will eventually die because without leaves, it won’t be able to process sunlight for chlorophyll or take in nutrients. Do not compost garlic mustard flowers or seeds. Research has shown the seed remains viable in soil for about five years.

Alternatives: Grow arugula and other strong flavored lettuces or greens, and onions, garlic or chives.

Japanese honeysuckle vine

japanese honeysuckle
Japanese honeysuckle vine flower
Photo courtesy University of Illinois

Japanese honeysuckle vine (Lonicera japonica)) smells wonderful in spring as it clambers along the fence and up the trellis. A vigorous grower, the vine has spread beyond the back yard to woodlands in the Eastern United States, clogging pathways and smothering small plants. The flowers are yellowish-white. Several states have banned the sale of this plant, sometimes listed as ‘Halliana.’

What to do? Pull Japanese honeysuckle from the ground whenever you can. It also can be treated with a weed killer, but because it is a woody plant, make sure the product is approved for that use. The best way to apply is to cut off the vine as close to the ground as possible and apply the herbicide to the remaining stump. Always read and follow the label of the product.

Alternatives: Any of the honeysuckle vine hybrids, including ‘Dropmore Scarlet,’ ‘Mandarin’ and ‘Goldflame.’ The latter is fragrant and attracts hummingbirds.

Honeysuckle shrubs

honeysuckle shrub
Berries on honeysuckle shrub
Photo courtesy Purdue University

Honeysuckle shrubs were introduced as ornamental plants from Japan more than 100 years ago. Today, these shrubs have taken over native plantings along creek banks and in woodlands. These honeysuckle shrubs leaf out earlier and stay green longer than native species, a trait that shrouds out native flowers and other plants. These shrubs have flowers and produce red berries, which birds like and are credited with helping to plant seeds in unwanted places. These shrubs are no longer commercially available in the United States.

judd viburnum
Judd viburnum flower
© Jo Ellen Meyers Sharp

What to do? Pull small saplings by hand as they appear in the garden. Keeping the top of the shrub pruned back to the soil will eventually starve out the plant. There also are specialized tools that can be used to pull or pop large shrubs from the soil. Or, chop off large shrubs and paint the stump with an herbicide recommended for woody plants. It may take a couple of treatments to kill the shrub. Always read and follow the label directions of the product you use.

Alternatives: Almost any viburnum shrub would be a good alternative to honeysuckle. Some viburnums are fragrant, such as ‘Judd’ or Korean spice, and many have spectacular fall color and berries. A few, such as leatherleaf and ‘Burkwood’ viburnums are semi-evergreen, holding their foliage well into winter.

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