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PlantFiles: Pale Swallow-wort
Cynanchum rossicum

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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

Category:
Vines and Climbers

Height:
4-6 ft. (1.2-1.8 m)

Spacing:
Unknown - Tell us

Hardiness:
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

Danger:
All parts of plant are poisonous if ingested

Bloom Color:
Brown/Bronze

Bloom Time:
Late Spring/Early Summer
Mid Summer

Foliage:
Smooth-Textured

Other details:
May be a noxious weed or invasive
Self-sows freely; deadhead if you do not want volunteer seedlings next season

Soil pH requirements:
Unknown - Tell us

Patent Information:
Non-patented

Propagation Methods:
Unknown - Tell us

Seed Collecting:
Unknown - Tell us

Click thumbnail
to view:

By BobCrystal
Thumbnail #1 of Cynanchum rossicum by BobCrystal

Profile:

No positives
No neutrals
3 negatives

Gardeners' Notes:

RatingAuthorContent
Negative coriaceous 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
mortality.

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 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 off close to the surface. This does no good. (Nor does weekly mowing.)

It's not difficult to dig out, with the right tool. The fleshy roots radiate from a node about 2 inches below the surface (like tentacles radiating from the head of an octopus). If you can just dig that node out, you're generally good. I use a cast aluminum trowel for this, using a prying motion. This plant won't regenerate from broken roots unless there's a bit of that node tissue attached.

Very old plants may have several nodes along a vertical rhizome, and may require a little deeper digging. But most just have one.

Any nodes you've missed will signal you by sending up a new stem within a week.

Where you can't dig out the node---this plant often seeds into cracks in pavement and masonry---you can paint it with concentrated generic glyphosate herbicide. Do this when topgrowth is mature but before it can go to seed. (I do this around July 1 here in Z6a.) Buy the generic 41% concentrate and dilute it only to 25% by adding one part water to two parts concentrate. Cover all available green surface. And you may sometimes need to do this a second time, the next year.

One thing that's in your favor: this plant doesn't leave lots of dormant seeds in the soil. Unlike many persistent weeds, which can be controlled but not eradicated, you can actually eradicate this from your yard.

If your neighbors have this too---a good bet---don't despair. Over 99% of the seeds land within 10' of the parent plant. You'll need to monitor your property in June and July for the occasional pioneer invader, but you won't get masses of seedlings from seeds drifting in on the wind. The important thing is to keep any plants on your property from going to seed.

Negative greenthumbs 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 (24.43.24.85).

Negative BobCrystal 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.

Regional...

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

Rochester, New York
Newport, Rhode Island



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