They are sets and bulbs that I bought and planted. I planted them probably 4 weeks ago. They have established roots. The tops on the bulbs are about an inch tall and the tops on the sets are a few inchesIt all depends. Are they sets you recently planted? Are they seedlings that you started in the house? How tall are the tops? If you've recently planted sets, they should be fine down to 20*, according to the literature. if they are seedlings that you've recently set out, I'd plan to cover them.