None of the milkweed varieties are perennial here in zone 7 so it has to be started by seed. The plants are challenging to locate and if you can find it, the cost is ridiculous, well, unless you want to have Monarch families.
The one year I purchased tropical milkweed, I dug it up in the fall and replanted it the following spring. That's always an option if you want to protect your investment. I start seeds each winter after a period of cold stratification in the refrigerator or by winter sowing in containers outside.
Monarchs are one of the few butterflies that migrate twice a year. We usually get a few in the spring but a lot in the fall. During the drought years they avoid us, seeking better egg laying ground but this year's rain should put them back in our gardens.
Recently I thought I saw Monarchs while outside weeding and pruning, but since other butterflies can resemble them when they flutter by so fast, I doubted my eyes. The caterpillars on the plants I saw today (photos above) reveal that they were indeed Monarchs.
As you can see, other butterflies mimic the Monarch. Birds have learned to avoid Monarchs because they taste nasty and make them feel less than optimal - Monarch's primary food, milkweed, is toxic. So, other butterflies adapted for the safety of their survival. Click over to the UC Santa Barbara link above for a more detailed piece about that topic.
Skippers, bees, wasps, butterflies and all their flying friends are welcome in our garden. We feed them, put up bee houses, leave tall grass for their cover on rainy days and celebrate them when we see them.