Gardening Laidback Gardener Tip of the Day Weeds

Bindweeds: Stranglers with Pretty Flowers

20160728A Derek Harper, Creative Commons
Hedge bindweed (Calystegia sepium). Photo: Derek Harper, Creative Commons

The name bindweed usually refers to a climbing or creeping plant in the Convolvulaceae or morning glory family. There are several species in different genera, but the two most often seen in gardens are hedge bindweed (Calystegia sepium, formerly Colvolvulus sepium) and field bindweed (Convolvulus arvensis).

There is also a third plant commonly called bindweed, but that is in no way related to the true bindweeds: black bindweed (Fallopia convolvulus). More on this plant at the end of the text.

True Bindweeds

First, let’s look at the true bindweeds (the morning glory relatives).

The two species are quite similar in appearance, with white or pale pink funnel-shaped flowers that open early in the morning and close around noon. Also both species have arrow-shaped leaves that are similar enough in shape to cause some confusion. However, their identities are clearly given away when they bloom, for the hedge bindweed has much larger flowers, 2 to 2 ¼ inches (5-6 cm) in diameter compared to the tiny but pretty ¾ to 1 inch (2-2,5 cm) blooms of field bindweed. In fact, hedge bindweed is a larger plant all around, with larger leaves 2 to 4 inches/5 to 10 cm long and stems that can climb to 20 feet (6 m) high under the right circumstances.

Field bindweed (Convolvulus arvensis) is a smaller plant with smaller flowers.

Field bindweed, on the other hand, has leaves half that size (1 to 2 inches/2-5 cm long) and rarely grows more than 6 feet (2 m) tall.

They get their name from their twining habit as, if given a chance, they will “bind” other plants together is if with rope. Their twining stems can cover and crush nearby plants – even shrubs or small trees! – with their weight. Plus they cover their host plants with their dense leaves and cut off their light.

Both plants were accidentally imported from Eurasia into gardens worldwide and are now considered cosmopolitan weeds. They multiply to a certain degree through seeds, but even more so thanks to under ground rhizomes (creeping stems) and roots, both of which can produce new shoots. Thus, once established, they readily invade nearby plantings. A single plant can send its rhizomes out in all directions, covering a diameter of up to 10 feet (3 m) in a single year.

Don’t Waste Your Time Hoeing

Bindweed rhizomes tend to grow laterally just under the soil’s surface, but the roots can reach down 20 feet (9 m) into the ground, making controlling them by cultivating or hoeing unrealistic.

Worse, cultivating tends to chop their roots and rhizomes into segments, each capable of starting a new plant. As a result, the more you cultivate, the worse the problem gets.

Worse yet is rototilling, which chops and widely distributes rhizome and root segments.

Two Slow But Effective Treatments

Cut bindweeds to the ground to exhaust their underground storage organs.

The most ‘logical’ way of controlling bindweed is simply to cut the stems to the ground… and to repeat this pruning every time they regrow. This works because, like all green plants, bindweed needs leaves to carry out photosynthesis and to build up its reserves. If you keep cutting the plant back, depriving it of all its leaves, thus of any new source of energy, you’ll gradually weaken it.

And I do mean gradually. Well-established plants can have a considerable root and rhizome system, with plenty of reserves stored away. One simple trimming will barely slow them down. But if you prune back again each time they sprout, in other words, every 2 to 3 weeks, and keep it up for 2 growing seasons, you will be able to exhaust them to the point where they simply die.

Don’t cry victory too soon, though: there can still be some regrowth up to 5 years later, at least in the case of hedge bindweed. That’s because it produces tiny buds on its roots that can remain dormant for several years, sort of Mother Nature’s backup plan. However, these buds use up all their stored energy in producing a single shoot. It you cut back the young plant during its first few weeks of life, it won’t be able to grow back.

While cutting back to the ground will eventually kill bindweed, simply mowing with a lawnmower won’t necessarily do the job. Field bindweed, especially, will cling tightly to the ground when it has nothing to twine onto and remains very low-growing, staying below the blades of a typical lawnmower. It is, in fact, a common lawn weed in many areas for that very reason. Mowing may however get rid of hedge bindweed, which is a taller growing plant and therefore likely to be whacked back entirely by a mower blade. It’s more of a garden or hedge weed than a lawn weed.

The Tarp Method

The other possibility is to cover the plant with an opaque tarp. This is also the most laidback way of controlling bindweed.

Cover the plant with an opaque tarp to cut off its access to sunlight and that will gradually exhaust its energy reserves.

In spring, place a black polyethylene tarp (or an old carpet!) over the entire surface and hold it in place with stones, bricks, potted plants, or mulch. The tarp should cover a surface greater than the plant’s diameter, otherwise it will quickly send out rhizomes beyond the exclusion zone.

You’ll have to leave the tarp in place for 2 years in this case (one year is sufficient for most other invasive plants) because of the considerable underground energy reserves of a mature bindweed plant. In the darkness under the tarp, deprived of light, the plant will no longer be able to stock up on solar energy and will slowly exhaust its reserves.

Even after 2 years, it is still possible to see some regrowth coming from dormant buds (mentioned above), but if you cut these stems to the ground as soon as they emerge, you will eliminate them: they don’t have the reserves needed to sprout multiple times.

Herbicides as a Last Resort

I’m not an avid fan of herbicides and personally avoid them in my own gardening, but if you’ve reached the point where you’re thinking of going in that direction, at least avoid spraying these products on bindwind, because you inevitably kill the desirable plants nearby.

20160728EThe secret to a relatively rational use of a toxic herbicide is to paint it onto the foliage of the unwanted plant: yes, with a small brush. Thus, only the plant you want to eliminate will be absorbing it.

Soap, citric acid, acetic acid (vinegar) and other organic herbicides will only kill the foliage and not the roots and rhizomes. Therefore the plant will tend to grow back fairly quickly. As a result you have to apply them repeatedly, probably for 2 years, until nothing grows back, just as the methods in which you control bindweed by excluding light.

Systemic herbicides, however, such as glyphosate, will kill the roots and rhizomes as well, as they are absorbed into the plant’s sap and then circulate throughout the plant’s system. They can eliminate the entire plant with only one or two treatments if you apply them correctly.

The best time to apply a systemic herbicide on bindweeds is when the plant is in bloom, because that is when the plant begins to prepare reserves for the following year and therefore when a lot of sap flows towards its roots and rhizomes. And it is precisely the roots and rhizomes that you’ll want to kill. If you paint the herbicide on the leaves at this season, it will be carried down to the deepest rhizomes and roots.

Keep on Checking

Even if you think you’ve won the war against bindweed, its seeds can remain dormant for 50 years or more. Fortunately young seedlings will not yet have had time to create underground energy reserves and even a quick hoeing will kill them. In addition, bindweed seeds will only germinate when they are exposed to sunlight. They won’t germinate in a densely planted garden or under a thick mulch.

A Bindweed Copycat

Black bindweed  (Fallopia convolvulus) looks much like true bindweed, but has insignificant flowers.

As mentioned at the beginning of this text, there is a third common bindweed, black bindweed, also called wild buckwheat (Fallopia convolvulus, formerly Polygonum convolvulus) that is totally unrelated to the true bindweeds. It’s a type of knotweed, that is a member of the Polygonaceae rather than the Convolvulaceae.

Black bindweed is an annual native to Eurasia and Africa, but is now distributed worldwide. It is easy to understand the confusion with true bindweeds (Calystegia and Convolvulus), as it is likewise a climbing or creeping plant with arrowhead leaves. However its tiny insignificant greenish, whitish or pinkish flowers, grouped in small sparse spikes, in no way resemble the attractive funnel-shaped flowers of true bindweeds and are a sure sign that this plant really is in no way related to them. The flowers turn into black seedheads at maturity, giving the plant its common name, black bindweed.

When you find this plant in your garden, hoe it down, pull it out or cut it back, using whatever is your preferred method of weed control. Remember it is an annual: it will not sprout from its roots the following year. Remove the plant early in the season, before it goes to seed, to help reduce future infestations. However, its seeds can survive for many years (one study found 22-year-old seed still viable!), so just eliminating the plant early won’t always guarantee perfect control.

Black bindweed is, however, very easy to control in future years if you just cover the soil in the spring with at least 5 cm of mulch. That will prevent any seeds from germinating.

In conclusion, bindweeds are not easy to control, but if you put a little effort into it, you can overcome them.20160728A Derek Harper, Creative Commons

1 comment on “Bindweeds: Stranglers with Pretty Flowers

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