Question: What about when there's a chance of late frost or freeze in spring?
Answer: For a late frost: Buds, flowers and tender new foliage are vulnerable to frost, which can form on cold, still nights, particularly if it is clear. Lightweight nursery fabrics will protect against frost damage and can easily be removed and stored for the next event. Secure them against winds that may accompany cold fronts.
For a late freeze: Floating lightweight nursery fabrics can still gain you several degrees' worth of protection, provided they're draped over your plants prior to the low temperatures, and if they're left there until temperatures are back into the high 30s.
Some folks want to put a sprinkler under their fruit trees if a late freeze catches them in flower. That's something commercial growers do, but you have to be careful that the weight of the ice that forms doesn't break the branches. You have to leave the sprinkler running until the temperature has risen above freezing. It may be better not to do this unless you're familiar with the technique.