When do I start this process?
I live in central Michigan. When do I plant the seeds and set the jugs outside? Does this work for all vegetables and perennials? I'm especially interested in starting sea holly from seed. Any suggestions?
Most generally, you place the seed sown containers outside around the last week of December.
Regarding which vegetables and perennials, I can't think of on vegetable or perennial that won't come up via wintersowing. Here is a small list of vegetables: List of Vegetables. I'm not personally sure on sea holly, but you could always give it a try!