Experts tackle readers’ garden questions.
Q: I have lived in my house for 22 years and have only just acquired this very invasive stubborn “weed” that produces lavender-white flowers. I can’t find the starting point. But it pops up all over the garden. It winds around the plants like a snake. I go out and pull on it and a huge root comes up but before I can follow it further it breaks. A few days later, the weed is right back where I just dug it up. It is taking over the whole garden! I could pull it up every day and it would be bigger than ever the next day! It stretches all over the flower bed, at least 8 by 12 feet. What is it? How do I get rid of it?
Sue Bear, Citrus Heights
Bee garden writer Debbie Arrington: Your garden has gotten all tied up by field bindweed, a common and invasive garden thug.
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A member of the morning glory family native to Asia and Europe, field bindweed (Convolvulus arvensis) is a hardy perennial that spreads from extensive rootstock as well as from seed, according to UC Cooperative Extension master gardeners.
How deep are those roots? They’ve been found with viable buds as deep as 14 feet and can reach 20 feet down. Part of its persistence is that bindweed grows roots both vertically and horizontally. The lateral roots send out new shoots while also sending more vertical roots down. That allows the plant to spread quickly; one field bindweed can cover a 10-foot circle in one growing season, according to UC research.
That extensive underground network also allows bindweed to survive winters without foliage, then start right up again in spring stronger than ever.
Ridding your garden of this plant takes vigilance. Field bindweed can persist for many years, resprouting spring after spring. Small sections of root or rhizome, as small as 2 inches long, can create a whole new plant, too. In addition, bindweed grows from seed that can remain viable for decades. Bindweed can sprout from seed 60 years old.
This weed has deep California roots, too. Field bindweed was first reported in San Diego in 1884. By the 1920s, bindweed was declared the worst weed in California.
As you described, bindweed winds around anything vertical, often other plants. As it grows up, it smothers its support and overwhelms other plants.
Very drought tolerant, bindweed can out-compete other weeds and ornamental plants with limited water. It can really take over during long periods of drought, such as we’ve recently experienced. It favors heavy clay soils, such as those common in the Sacramento area.
Unfortunately, control of field bindweed is not easy. There’s no single treatment of an herbicide that’s effective. It will take more than a single season to make it disappear.
According to UC research, effective control requires: prevention of seed production, reduction of stored carbohydrates by deep tillage of the root system, competition for light from other plants and constant vigilance in removing top growth.
Bindweed needs sunlight to grow. It may be smothered by sheet mulching, but that won’t help your shrubs. Landscape fabric or weed cloth stretched around shrubs and covered with organic mulch may cut down on the spread of the bindweed; make sure the pieces of fabric overlap so the bindweed can’t find its way to light.
Even with mulching, the bindweed rhizomes will remain viable for three to five years and can resprout if they get light.
Herbicides can help suppress bindweed but not eradicate it. According to UC research, products containing trifluralin, oryzalin or pendimethalin applied before emergence will reduce perennial shoots and control the germinating seedlings, but those pesticides won’t kill established bindweed plants.
Roundup or glyphosate can be painted onto the bindweed foliage and slowly kills the plant, but repeated applications are necessary. Care must be taken to prevent glysophate from touching other desirable plants. This herbicide should not be used around roses.
For more information on control of field bindweed, visit http://ipm.ucanr.edu or send a self-addressed, stamped business-size envelope to: Pest Note 7462, UC Cooperative Extension, 4145 Branch Center Road, Sacramento, CA 95827.
Contact The Bee’s Debbie Arrington at email@example.com. Follow her on Twitter @debarrington.
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