Pale Swallow-wort

Cynanchum rossicum

Family: Asclepiadaceae (ass-kle-pee-ad-AY-see-ee) (Info)
Genus: Cynanchum (sigh-NAN-chum) (Info)
Species: rossicum (ROS-ih-kum) (Info)
Synonym:Vincetoxicum rossicum
Synonym:Cynanchum medium
Synonym:Vincetoxicum medium


Vines and Climbers

Foliage Color:

Unknown - Tell us

Bloom Characteristics:

Unknown - Tell us

Water Requirements:

Unknown - Tell us

Where to Grow:

Unknown - Tell us


4-6 ft. (1.2-1.8 m)


Unknown - Tell us


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


All parts of plant are poisonous if ingested

Bloom Color:


Bloom Time:

Late Spring/Early Summer

Mid Summer



Other details:

May be a noxious weed or invasive

Soil pH requirements:

Unknown - Tell us

Patent Information:


Propagation Methods:

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

Seed Collecting:

Unknown - Tell us


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

Iowa City, Iowa

Rochester, New York (2 reports)

Newport, Rhode Island

Gardeners' Notes:


On Sep 9, 2017, Conan from Rochester, NY wrote:

This plant is spreading all over Monroe County NY - displacing other woodland plants. Seems to thrive in both shade and full sun very drought tolerant. Very hard to control. You must dig out the roots completely to kill the plant. Once the pods form and open, seeds disperse much like Milkweed.
The parks here are all infested with his, has grown noticeably more invasive in the past couple of years.


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

This is a perennial weed and an invasive plant destructive of natural areas over a wide swath of northeastern and midwestern North America. It's also a terrible pest in the garden and yard. It twines with astonishing speed up fences and about anything standing still nearby---it isn't called 'dog strangling vine' for nothing.

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

Trade, transport, and planting this species is illegal in my state and two others.

It does best in full sun, but it also grows well in shade.

My experience is with the closely related black swallow-wort, V. louisae, but these two species are very similar. Here's what I've written about how to deal with them:

It's lat... read more


On Aug 9, 2003, greenthumbs from Toronto,
Canada wrote:

Very negative. Toronto, Summer 2002, there were a few plants on my small property. I thought they were some form of milk weed and was not particularly concerned. The excessive daytime heat prevented me from staying ahead of the problem. This year there has been an explosion in the number of these aptly named "dog-strangling vines." With the assistance of a horticultural landscaper, we have managed to remove the pods and many of the mature plants - 6 large leaf bags worth. I found a site with some info re: chemical and mechanical control - it is the Ontario section of Invasive Plants of Canada website (


On Jun 30, 2003, BobCrystal from Rochester, NY wrote:

This weed reappears in my garden, hedge and bushes every year.The flowers are small, like belladonna without the central yellow and they really are BROWN. Thanks to Giorio in the Forums section, I now know it is Cynanchum rossicum , swallowtail, a relative of the milkweed.