I'm new to raising butterflies this year and also new to growing milkweed. I ran out of tropical milkweed to feed my Monarch cats this summer and it really cost me a lot to round up food for them so want to be better prepared next year. :-)
I purchased 80 starts of Swamp Milkweed late this summer and transplanted them into cups of potting soil. Some cups are 8 oz size styrofoam and some are 12 oz clear plastic (of course, with punched holes in bottoms of all cups). I currently have them sitting on my deck.
We live in zone 7b, central Arkansas. I am wondering if I should keep them in a cool greenhouse until spring or leave them sitting on the deck through the winter months? The plant guide says they're hardy to zone 3a so I assume the roots can be frozen and still come back in the spring? In the greenhouse during sunny days of winter, I assume it will become warm during the day (first year with greenhouse) and I intend to always keep night temps above freezing so would those temps confuse the plants. Being perennial, are they expecting to be frozen during their dorment rest period?
They currently don't have any leaves on them, just look like little sticks right now. I pulled one up and it didn't appear the roots have grown anymore from what they looked like when I planted them as plugs.
My thanks for your advice.
Mary
Swamp Milkweed plugs - how to overwinter
I can't tell you for sure with swamp milkweed, but in general, roots in those small containers, up on the deck, are going to get a lot colder than roots planted in the ground, insulated by The Earth, even if they're farther north. So I would feel hesitant about leaving them there.
It looks like the recommendation is "unheated greenhouse" which it sounds like is what you have. When I have young plants in those small containers, I usually burrow them into the flower beds, with a lot of mulch. Kind of like heeling in a tree? So they're not as insulated as the ground, but they've got some protection.
Hope that helps...
I would put them in the ground for sure. The containers like RBL said don't offer much protection. They will die back but put out growth in the spring.
You wanted to know if these plants have to have a winter cycle. I don't know for sure, but some cold weather with the soil above freezing might encourage better root growth. That is one of the purposes autumn serves here in zone 5 - the top takes a rest while the roots take their turn growing. If they don't seem to be rooting, you might try some liquid root stimulant.