Basjoo is pretty tough once it gets established, I have several clumps from seed that have been in the ground for over ten years with no protection. I would suggest that you wait until your plants are at least a foot or more tall before you think about putting them in the ground. Wait until your soil warms up, probably around mid June. mature basjoo can handle cool conditions, they just won't grow much. Don't forget to harden them off before planting them outside. Give them plenty of water and fertilizer during the summer and stop feeding in the fall. After the first hard frost cut the stalks back to about a foot and mulch heavily. If you have wet winters the corms tend to rot. Plant in full sun.