I cannot find a definitive answer online about this, so I thought I might try here, in case anyone familiar with this type of milkweed knew. I found that Asclepias Tuberosa (Butterfly Weed) doesn't have the milky sap that the other milkweed have like common milkweed. So I was wondering if this is even a suitable host for the monarch caterpillar because of that? EDIT: Reason I ask is because I currently have common milkweed planted in my garden but it is too invasive and spreads quickly via rhizomes. Although monarchs lay eggs on it and I have two caterpillars currently feasting on it. I wanted to replace it next year with a milkweed that is less invasive (if there is such a thing)
It seems that it is a host species for monarch caterpillars, but not the preferred species. The adults feed from the flowers and it has many other good features for the environment, so it's certainly not bad to plant. Asclepias tuberosa (Butterfly Milkweed, Butterfly Weed, Chieger Flower, Chiggerflower, Common Butterfly-weed, Indian Paintbrush, Milkweed, Pleurisy Root) | North Carolina Extension Gardener Plant Toolbox Lady Bird Johnson Wildflower Center - The University of Texas at Austin Monarch Danaus plexippus (Linnaeus, 1758) | Butterflies and Moths of North America
Consider finding a way to grow the common milkweed in a confined space (e.g., half-barrel container). You'll also want to remove the developing fruit every year, but that is only a few minutes of maintenance once in a while. This gives you the larval host plant in a controlled way.
If I had known a few years ago just how invasive Asclepias tuberosa ‘Gay Butterflies’ would be, I would have planted it somewhere different from where I did. Probably in a container as @Daniel Mosquin suggests. Invasiveness aside, it is a gorgeous plant so, if it does attract monarch butterflies, all the better. Beggars can't be choosers.
Are any of these milkweeds hardy enough to survive the Canadian winter in a container if left outside? (i.e. not bring it into shed or garage)
Hmm. Good question. The general rule I had heard for around here on the west coast is 2 zones difference for containers -- so in the parts of Vancouver that are zone 8, you can predict that zone 6 plants should survive (and yes, it's a general rule). If the same were true for southern Ontario, common milkweed would easily fall within that rule (since it grows in Manitoba, too).
Here is a good write-up about growing milkweed species in Ontario. Even though it doesn't mention zones specifically, the fact that it encourages Ontarians to grow the plant suggests that several types grow there. Monarchs Need Milkweed — Ontario Native Plant Nursery | Container Grown | (705)466-6290
