There are few summer sights more delightful than that of butterflies spotted flitting back and forth amongst a beautiful garden — and given that monarch butterflies in particular have been in greater and greater need of conservation efforts in recent years, butterfly gardens aren’t just pretty; they’re necessary. And hey, guess what? If you want to grow a butterfly garden yourself to pitch into the conservation effort, you only need to plant one kind of plant to attract monarch butterflies. What’s more, you’re probably already familiar with it. It tends to grow by the road, in fields, and in parks — heck, my elementary school had a whole bunch of it growing in the woods behind the playground. I’m talking, of course, about milkweed.
Monarch butterflies are well-known for their distinctive orange, black, and white markings and their migratory patterns. Monarchs that hatch in the eastern areas of North America migrate in the late summer and early fall to warmer climates in Florida and Mexico, while monarchs that hatch in the western areas of North America tend to migrate to southern California and Mexico each year. But before they can spread their brightly-colored wings, they have to make it successfully from egg to larva, from larva to pupa, and finally from pupa to adult butterfly.
That’s where milkweed comes in. Monarch butterflies lay their eggs exclusively on milkweed plants, because those plants are pretty much the only thing that monarch larvae eat. The eggs hatch roughly three to five days after being laid — and although the newly-born caterpillars generally start by eating the egg cases they just hatched from but no longer need, after that, they spend about two weeks eating milkweed, getting bigger and molting a few times as they do so. After these two weeks are up, they spin their chrysalises — the hard, protective shells that keep them safe while they metamorphose — and after another two weeks, they emerge from their chrysalises as butterflies.
So: If you want to attract monarchs to your yard, you’ll need to make sure there’s some milkweed around for them. But how much should you plant? Which variety? And what do you need to do to take care of the plants to ensure they’re an attractive spot for monarchs to lay their eggs?’
The good news is that milkweed is quite easy to grow and largely self-sufficient once it’s been planted. According to gardening website Gardner’s Path, common milkweed, or Asclepias syriaca, “does well in what might be considered average conditions”: If your soil is “moderately dry and well-draining,” and the spot in which you’ve planted your milkweed gets roughly eight hours of sunlight a day, the plant should do fine without any special fertilizers or other garden treatments. You don’t even really need to give it any extra watering, unless you’re experiencing a particularly dry season.
That said, though, you’ll want to pick exactly which kind of milkweed you plant based on what’s native to your region. The Monarch Joint Venture, which brings state agencies, non-governmental organizations, and academic programs together in order to help protect and preserve monarchs and their migration patterns, has an excellent fact sheet that helps identify which varieties are best for which regions in the United States depending on their climate; according to this fact sheet, butterfly weed and whorled milkweed tend to do well in a lot of different regions, but you’ll definitely want to choose carefully before you go ahead and plant anything. Butterfly weed has the added benefit of blooming beautiful orange flowers, so if you want something colorful and you’re in a region appropriate for it, that’s likely going to be a good choice for you.
As for how much you should plant? Again, that depends. According to the University of Minnesota’s Monarch Lab, one monarch caterpillar usually eats about one whole milkweed plant between the time when it hatches and when it spins its chrysalis, which should give you a baseline of how much to plant. Bear in mind, though, that the amount of milkweed any single caterpillar eats can vary depending on the variety of plant; some types of milkweed have narrower leaves than others do, which means the caterpillar might need to eat more than one plant before it enters the pupal stage.
Milkweed can be grown either from seeds or from seedlings, according to Monarch Butterfly Garden. If you plant them early enough, you can grow them from seeds (think in the fall, right about when milkweed plants naturally drop their seeds); if you plant them in the spring, though, you’ll want to plant roots or potted seedlings.
When it comes to actually acquiring milkweed to plant, you can forage if you actually know what you’re doing (I certainly don’t, but the University of Minnesota’s Monarch Lab has some useful tips on how to find it if you’re a better forager than I am ) — but it might be simpler and safer if you look for it at plant nurseries near you. Heck, the gardening department of your local Home Depot might even have some available, if your nursery options are slim where you are.
You could try ordering online, too, although as the website Monarch Butterfly Garden points out, you’ll want to make sure you do your homework on the seller before you place an order. House Beautiful points out that there are even some sellers on Amazon from whom you can get milkweed roots — but if you choose to go that route, you’ll want to vet your purchase extra carefully before you place your order. First off, you want to make sure you’ll be getting healthy roots; and second, you want to make sure that the variety you’re buying is native to the United States, not a tropical variety (reviewers of this Amazon listing, for example, caution that the variety sold is tropical). Why? Because according to a study published in 2015, tropical milkweed varieties can actually endanger monarchs, rather than help them.
There are two issues with tropical milkweed, as Science Magazine highlights. First, they don’t “die back” — that is, when they’re planted in warm environments like the southern areas of the United States, they stay alive year-round. When that happens, monarchs, too, can lay their eggs year round, which gives them no reason to perform the great migration that’s characteristic of their life cycle. But second — and perhaps more pressingly — the tropical varieties are more susceptible to a type of parasite that kills the butterflies before they’ve finished out their full life cycle. The study, which was published in the Proceedings of the Royal Society B., found that monarchs that don’t make the late summer/early fall migration due to the presence of tropical milkweed in the area in which they hatched were five to nine times more likely to fall prey to this parasite than butterflies that undertook the migration were. Again, check out the Monarch Joint Venture’s fact sheet on what kinds of milkweed are best for your region — it can make a big difference when it comes to monarch butterfly conservation.
Also, something extra worth noting: Milkweed is toxic to dogs, cats, and horses, according to the ASPCA, so if you take care of these animals yourself or live near any who have access to your backyard or garden spaces, you might want to avoid planting milkweed. This means you might not be able to cultivate a butterfly garden specifically for monarchs, but you might still be able to grow other kinds of plants that will attract a variety of butterfly species.