Black Swallow-wort, Dog-strangling Vine, Louis' Swallow-wort

Cynanchum louiseae

Family: Asclepiadaceae (ass-kle-pee-ad-AY-see-ee) (Info)
Genus: Cynanchum (sigh-NAN-chum) (Info)
Species: louiseae
Synonym:Cynanchum nigrum
Synonym:Vincetoxicum nigrum



Vines and Climbers

Foliage Color:

Unknown - Tell us

Bloom Characteristics:

Unknown - Tell us

Water Requirements:

Average Water Needs; Water regularly; do not overwater

Where to Grow:

Unknown - Tell us


4-6 ft. (1.2-1.8 m)


24-36 in. (60-90 cm)


USDA Zone 4a: to -34.4 C (-30 F)

USDA Zone 4b: to -31.6 C (-25 F)

USDA Zone 5a: to -28.8 C (-20 F)

USDA Zone 5b: to -26.1 C (-15 F)

USDA Zone 6a: to -23.3 C (-10 F)

USDA Zone 6b: to -20.5 C (-5 F)

USDA Zone 7a: to -17.7 C (0 F)

USDA Zone 7b: to -14.9 C (5 F)

USDA Zone 8a: to -12.2 C (10 F)

USDA Zone 8b: to -9.4 C (15 F)

USDA Zone 9a: to -6.6 C (20 F)

USDA Zone 9b: to -3.8 C (25 F)

Sun Exposure:

Full Sun

Sun to Partial Shade


Parts of plant are poisonous if ingested

Bloom Color:


Bloom Time:

Late Spring/Early Summer

Blooms repeatedly



Other details:

May be a noxious weed or invasive

Soil pH requirements:

5.6 to 6.0 (acidic)

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

Patent Information:


Propagation Methods:

Self-sows freely; deadhead if you do not want volunteer seedlings next season

Seed Collecting:

Bag seedheads to capture ripening seed

Allow pods to dry on plant; break open to collect seeds

Allow seedheads to dry on plants; remove and collect seeds

Properly cleaned, seed can be successfully stored


This plant has been said to grow in the following regions:

Boston, Massachusetts

Bridgewater, Massachusetts

Hull, Massachusetts

Waltham, Massachusetts

Davisburg, Michigan

Warren, Michigan

Helena, Montana

Farmington, New Hampshire

New Milford, New Jersey

Rochester, New York (2 reports)

Seattle, Washington

show all

Gardeners' Notes:


On May 10, 2017, MTVineman from Helena, MT (Zone 5a) wrote:


On Sep 21, 2014, tutusmith from Davisburg, MI wrote:

Just found this vine on our property in Davisburg, Michigan. Not happy after seeing how it is climbing up and trying to choke out other plants. Seems it will be very hard to get rid of on our acreage as it takes digging or using roundup which I try to avoid as it is poisoning our soil everywhere. Please do not plant this if you do not have it already.!!! It is a problem for the Great Lakes region and can cause Monarch caterpillars to die after they are laid as the vine is not their food.


On Feb 21, 2014, coriaceous from ROSLINDALE, MA wrote:

I've seen this noxious weed replace grass in lawns and meadows. It also grows well in shade.

This is a perennial weed and an invasive plant destructive of natural areas over a wide swath of northeastern and midwestern North America (and California). Its planting, trade, and transport is illegal in my state and three others.

And, yes, it's responsible for significant Monarch butterfly

It's late to emerge from dormancy, often not till June in Z6a. It begins to shed seeds in late July and continues till frost. If you cut the stems or harvest the seedpods, it can produce more that same season.

At least it IS possible to eradicate it from your yard. Here's how:

Just pulling on the stem makes it snap of... read more


On Jan 21, 2014, RCCWMA from Little Canada, MN wrote:

This plant is a noxious weed in the State of Minnesota (and others). Do not plant it. It is also a plant that is detrimental to the monarch butterfly population. Butterflies are confused by this plant and lay eggs on it, but the caterpillars die. If you have this weed on your property, please get rid of it.

Please always check to see whether that new and interesting plant is invasive before planting. This is easy to do online. Just type in the common or scientific name and the word "invasive". Thank you!


On Jun 4, 2013, Jadwin59 from Rochester, NY (Zone 6a) wrote:


*Please don't cultivate this plant.* It's invasive, very difficult to eradicate, and it kills butterflies that mistake it for the more beneficial milkweed. It will choke out everything else in your garden and spread, through its floating seedpods, all around your neighborhood.


On May 19, 2013, Dean48089 from Warren, MI (Zone 6b) wrote:

I originally found this plant growing in a sidewalk crack. The glossy leaves and black flowers looked interesting, so I snatched a seed pod and raised some seedlings. At the time I was gardening in sandy loam with a lot of shade, where this plant stayed small and grew 2-3 feet up the fence. My new house, where I still live, has heavy clay soil and lots of sun -- where the black swallowwort quickly turned into a monster. Besides filling the air with billions of seeds, which germinate immediately as soon as they land, it also spreads via underground stems. The waxy leaves repel all herbicides and any little bit of root left in the ground will quickly turn into a new clump.

A local specialty nursery used to sell this plant because it is apparently the food source for a par... read more


On Jul 30, 2012, theoldhorse from Hull, MA wrote:

This is an absolutely TERRIBLE INVASIVE WEED. It will grow quickly up and engulf adjoining plants in your garden, entwining its single central stem and climbing other plant stems and foliage and jumping from plant to plant.
As it gets larger it produces many pepper-like seed pods that are heavy enough to weigh down other plants. The very tiny near-black precursor flowers are virtually unnoticeable having no aesthetic value whatsoever. It will spread from the garden to the lawn where mowing will not eliminate it.

It is extremely invasive and practically impossible to eliminate. Its central stem is attached to a spider weblike root system made up of hundreds of radiating and branching white roots. Even the smallest of plants cannot be pulled because the roots con... read more


On Feb 1, 2012, iloveperennials from Rochester, NY wrote:

This is probably THE WORST WEED I have on my acre...and that's saying alot because I also have poison ivy and bittersweet vine. It grows about 2-3 feet tall, twining around itself so you can't walk through it, hence one of its many nicknames 'dog strangle weed'. It makes winged seeds that the wind blows around. Roots are hard to get out IF the ground is dry. I'm trying to eradicate it by pulling it up by hand when the ground is moist but we're talking 1 plant/3 inches, BEFORE it goes to seed. You there in Seattle, who is growing it on purpose - HUGE MISTAKE! imho.


On Jun 30, 2010, LOVIE2 from Boston, MA (Zone 6a) wrote:

I hate this vine! It's taken over my yard and is trying to work it's way to my gardens. Round up for poison ivy works wonders!


On Jun 19, 2010, gregr18 from Bridgewater, MA (Zone 6b) wrote:

Extremely aggressive and extremely foul-smelling vine that can grow anywhere. It can strangle trees and shrubs with ease if given the chance. It smells like a dirty rabbit hutch or guinea pig cage. The smell gives me a headache. Although the dark green foliage can be attractive, I recommend killing this vine. Cut the stems close to the ground and dip the freshly wounded main stems in RoundUp concentrate.


On Feb 22, 2008, Malus2006 from Coon Rapids, MN (Zone 4a) wrote:

This is consider an invasive species in North America and acts as an attractive for Monarch butterflies to lay their eggs on it. The larvaes have a high death rate as the plants don't have the chemicals that the larvaes need for defense and also larvaes starves to death because swallow wort don't have the right kind of nutrients for them. This vine is currently the most common around New England, most of the Great Lakes area west to Wisconsin.


On Apr 21, 2006, MontanaVineMan from Helena, MT (Zone 5a) wrote:

This is a very interesting vine, I must say. So far, I have had a positive experience with it. How I acquired the plant is actually fairly funky. When I lived in Seattle, I was the landscape manager for a large and well known nursery. One day, the crew came back with this plant stuffed into a pot. They saved it as none of us had ever seen it before.

It had been growing in the middle of a patch of low growing Juniper! Obviously a very tough plant! I saved the plant for about a year or so in our company grow lot, in just a 5 gallon black plastic generic pot. I eventually moved back to my native state of Montana and brought this plant with me among countless others. I thought it would for sure die in our cold Winter climate as I had left it outside as an experiment. Well, surp... read more