I am new to planting milkweed. Is it too soon to plant 1 gallon plants in Michigan now?
I would not do it. You likely won't see monarchs until early June. If you want monarchs laying lots of eggs on your plants, you don't want old plants. I'd suggest having your milkweeds seeds sprouting around the 1st or 2nd week of May. The trick is to have young plants that are attractive to egg laying monarchs plus have enough leaves to feed the caterpillars.
In my experience, monarchs' favorite milkweeds to lay eggs on are around 2" tall. So when I say they like young plants, I mean YOUNG. Once you get your milkweed established, make sure you check the tiny plants that are coming up later in the year. They will come up from the spreading rhizomes.
The OP didn't mention the species on the milkweed or whether seedlings were to be started.
I knew that but your reminder made me think more about it. As someone who spent a lot of time in MI, I figure when a Michigander says "milkweed," she means common milkweed. But now I'm thinking you don't usually find common milkweed in 1 gallon pots, something I had not considered before answering.
So, Kris, what kind of milkweed are you talking about since my answer would not apply to all milkweed.