A.The answer totally depends upon what you are putting in your planters. I have already planted mine up with primula, tulips and daffodils. I did it last week and they should be fine now. If it gets very cold then I will cover them with something at night because they are completely out in the open. In the middle of May I will take those plants out, because most of them will be over. The primula can then be planted in a shady location in the garden.I wouldn't recommend doing your planters with annuals before around the 10th of May depending where you live and the choice of annuals.