Milkweeds for monarch caterpillars
Milkweed is NOT a "weed"! (And what's a "weed" anyway??)
REMEMBER: No milkweeds, no monarchs! Here's how to grow them.
Milkweeds are interesting plants with interesting flowers and an interesting history. Schoolchildren collected the pods in WWII to fill life jackets, and they're now experimenting with other ways to use the silk. I found one website business advertising "syriaca" bed comforters. I'm sure most people don't realize they're buying milkweed!
All species of milkweed are in the genus Asclepias. Thus, Asclepias tuberosa is butterfly weed, Asclepias incarnata is swamp milkweed, and so on. (I've found that learning the botanic names is really useful.)
Bee with pollinia stuck in milkweed flower
The milkweed flower's individual florets are intriguing.
Insects (in addition to butterflies) flock to get the nectar, but they sometimes get stuck in the flower.
Unlike many other flowers, milkweed flowers don't have pollen grains. They have structures called pollinaria instead. In their quest for the milkweed's abundant nectar, insects legs get stuck in the slit between the "hoods" of the flower. Most of them can pull away, along with the attached pollinaria, but some never make it or leave a leg behind.
Milkweeds native to the Northeast
Fields full of milkweed used to be a common sight; alas, no more. This CNY field is slated for someone's vacation home.
Below are some milkweeds native to the Northeast. (Additional milkweeds are native to other regions.) Some sources indicate that there are 72 milkweeds native to the US and 108 native to the continent, of which 30 (so far) have been shown to be used by monarchs.
Why native milkweeds? Many people grow tropical milkweed and assume just because the monarchs "like it" that it's a good choice. But there are lots of reasons for sticking with the natives (see the sidebar for a factsheet on this).
Most common milkweeds available here
Swamp milkweed (Asclepias incarnata)
In our yard, swamp milkweed is a monarch favorite. It's also a beautiful garden plant.
Contrary to its name, swamp milkweed doesn't grow only in a swamp or in wet areas, at least here in Central New York. (It may need more moisture in hotter climates.) Most of ours are growing in "regular" soil, though some are growing in the shallow edges of our pond.
We're growing them in sun and in part sun conditions, but they don't thrive in deeper shade.
Common milkweed (A. syriaca)
As the name indicates, common milkweed is a very commonly-seen milkweed growing in the wild.
(Or at least it used to be common before people started ripping it out as a "weed" — which is the reason we need to plant more.)
Common milkweed can be tall
It's great for monarchs and one of their favorites, but some people are reluctant to plant them in a home landscape since it spreads by traveling underground.
We don't mind, and although they come up here and there, we haven't found them to be a problem with a little management. We cut them back or simply yank out the errant stalks. (Be careful not to get the sap in your eyes!)
Regrowth after pruning
After a hard pruning, it regrows tender new leaves and doesn't reach its former height.
It's not very particular as to soil, though we wouldn't plant it in really dry soil. It does best in full sun, but we do have it growing (albeit less vigorously) in partly shaded conditions.
Unlike our other species of milkweeds, some of which are lightly scented, common milkweed has a glorious, heavy fragrance—my favorite plant for fragrance.
Butterfly weed (A. tuberosa)
Butterfly weed is a good milkweed for dry, sunny areas with poor soil, but like the swamp milkweed, I also grow them in "regular" soil. It does NOT like rich, moist soil.
The leaves are heavier and more leathery than the swamp milkweed, and I don't find as many eggs laid on these as I do on swamp or common milkweed.
I don't rely on these for monarchs, but they can support the growth of monarch caterpillars.
Other milkweeds native to our area
Poke milkweed (A. exaltata)
Poke milkweed is a good milkweed for shady areas.
We only have a few of these, but I've found monarch caterpillars on them, so this species would be a good choice for a yard that has less sun than ours.
Purple milkweed (A. purpurascens)
This is an absolutely gorgeous flower—such an intense, beautiful color! We only had one plant, and unfortunately, it died out.
I've read that it needs a genetically different individual to pollinate this in order to produce seeds. I've rarely seen it available for sale.
I didn't notice any monarchs interested in it, but I only had one individual plant of this compared to many, many swamp milkweeds.
Whorled milkweed (A. verticillata)
Whorled milkweed is a very slight plant, very delicate.
We have a small, but modestly growing patch of this type of milkweed, but we haven't noticed any eggs on it. One caterpillar could easily eat the whole thing!
A pretty little plant, but since I don't have a decent sized patch of it, it's probably not as useful for monarchs.
Close doesn't count!
Dogbane as seen by the road on our walk to Wegmans
Dogbane, one of which is hemp dogbane (Apocynum cannabinum), is a native relative of milkweed, and it also has milky sap. BUT it is NOT a host plant for monarch caterpillars.
It's easy to confuse milkweed and dogbane. I recognize this plant by its different branching structure.
Dogbane does happen to be a host for other moths and butterflies, though.
Swallowwort (both black and pale) is another milkweed relative, and it also does not support monarch caterpillars. It, however, is a non-native invasive plant.