Commentary

Ron Krupp: Identifying and controling invasive plants

Editor’s note: This commentary is by Ron Krupp, who is the author of “The Woodchuck Returns to Gardening.”

Every year, I identify and learn about invasive plants I wasn’t aware of. In 2019, I came in contact with three invasives including Japanese hops and wild parsnips in my community garden, and buckthorn while walking in Red Rocks Park in South Burlington which borders Lake Champlain and Shelburne Bay.  

JAPANESE HOPS (Humulus japonicas) — This summer, I saw an invasive in my garden at the Tommy Thompson Community Garden in the Intervale in Burlington. Japanese hops is native to Japan and eastern China.  This annual climbing/trailing vine was introduced to the United States as an ornamental plant in the mid- to late 1800s. Unlike its close relative, Humulus lupulus (common hops), Japanese hops have little value in the brewing industry.  By the way, common hops grow high in one of the perennial beds at the community gardens. 

Japanese hops is a dioecious, fast-growing, herbaceous vine in the Cannabinaceae family.  Its leaves are simple, opposite, heart shaped and palmately divided, usually into five lobes. Flowers are greenish and bloom mid to late summer. Green hops produced by female plants contain oval, yellowish brown seeds. The seeds are believed to remain viable in the soil for three years and are dispersed by wind and water along rivers and streams and in fields.  The stems are 8-35 feet in length and are covered with rough prickles that are irritating to bare skin. I can attest to that after removing them this summer. 

Plants can be hand-pulled and removed from the area before seeds ripen. When pulling the plants, attempt to remove as much of the rootstock as possible. Long sleeves, pants, and gloves are essential to avoid skin irritation. It is likely that resprouts could occur from both the rootstock and the vines. I pulled out the hops and also dug them out with a shovel. 

This hops species has a high reproductive rate, rapid growth rate, long range dispersal, and broad photosynthetic range. Japanese hops can form dense, almost solid, stands that outcompete native vegetation and have the potential to displace native riverbank and floodplain vegetation. Vines begin growth in May. Growth is rapid and the vines quickly climb over adjacent vegetation. 

Japanese hops can grow in sandy, loamy, clay, acid, neutral and basic soils. While it requires moist soil, it can grow in semi-shade to no shade environments. It threatens open woodlands, fields, prairies and riparian corridors. It is widespread throughout the eastern United States and ranges from Maine south to Georgia and west to Kansas and Nebraska. I’m sure I’ll be removing hops for years to come. 

WILD PARSNIP (Pastinaca sativa) — In the summer of 2019, I found some wild parsnips growing in my community garden plots. Wild parsnip, also known as poison parsnip, can be seen by its tall yellow flowers growing along roadsides across Vermont. It’s a dangerous plant as it can cause second-degree sunburns, painful rashes and blisters on your skin especially in the presence of sunlight. When I dug them out of my community garden, I wore gloves, long sleeves and pants. My garden neighbor wasn’t so lucky. He had burns on one arm.  

Poorly maintained swaths of land, like pastures, the roadside and abandoned fields, are notorious for hosting the tall yellow flowers, according to the Vermont Department of Health. Make sure to steer clear of this invasive species.

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Poison parsnip is often mistaken for its harmless lookalike, Queen Anne’s lace, which can be distinguished by its white flowers. The weed can grow up to 4 feet and looks and smells like cultivated parsnip. Its leaves have jagged edges, while leaflets are shiny, and diamond shaped. Wild parsnips are closely related to carrots, parsley, angelica and giant hogweed. 

Years ago, I left some sweet parsnips in the ground over the winter. Come early summer I didn’t harvest them, and they grew into 8-foot-tall plants. I harvested the parsnip seeds and planted them in my garden soil along with carrots, beets, turnips and rutabagas. I left the mature parsnips in the ground over winter and harvested the sweet roots come spring. There’s nothing better tasting.

COMMON BUCKTHORN (Rhamnus cathartica) – In my daily walks through Red Rocks Park with Hercules, my famous lab-newfie mix, I see more and more buckthorn. Under the direction of Ashley Parker, South Burlington staff naturalist, the city has undertaken invasive plant removal and control without the use of herbicides in both Red Rocks Park and Wheeler Nature Park. In my walks, I use garden clippers to remove the young buckthorns and loppers for the smaller trees.  

A method of control is to cut the stump and then return periodically to remove the growth that emerges from the stump thus weakening the tree from further growth. Under Parker’s direction, the Youth Conservation Corps has done much of the cutting. South Burlington has also sponsored several “Weed Warrior” programs led by Mike Bald of Got Weeds, a professional invasive plant removal expert, who trains volunteers on the proper removal techniques. 

The common buckthorn is an invasive to natural areas since it was introduced in the 1800s as a hedge row landscaping feature. It spreads easily by way of fruit (little black berries) scattered by birds. It is easy to identify since it is among the last to lose its color and leaves in the fall and first to appear in the spring. Buckthorn provides little nutrition to wildlife and inhibits the growth of native trees in forests by its leaf formation early and late in the season along with its hedge like structure. 

I didn’t mention poison ivy which grows rampant throughout Red Rocks Park. I’ve noticed how with the greater warming of our planet each year, poison ivy spreads more and more.    

You can help stop the spread of invasive plants by following these eight easy guidelines: 

1. Ask for only noninvasive species when you acquire plants. Request that nurseries and garden centers sell only noninvasive plants. 

2. Seek information on invasive plants. Sources include botanical gardens, horticulturists, conservationists, and government agencies. 

3. Scout your property for invasive species, and remove invasives before they become a problem. If plants can’t be removed, at least prevent them from going to seed. 

4. Clean your boots before and after visiting a natural area to prevent the spread of invasive plant seeds. 

5. Don’t release aquarium plants into the wild. 

6. Volunteer at local parks and natural areas to assist ongoing efforts to diminish the threat of invasive plants. 

7. Help educate your community through personal contacts and in such settings as garden clubs and civic groups. 

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8. Support public policies and programs to control invasive plants. 


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