|Lee Valley's Floating Covers|
|Lee Valley's Ventilating Cloche|
|Lee Valley's Garden Cloches|
I've also used in the past overturned plant pots, cloches, pop bottles (with bases cut off) which also work great. In windier situations, place a large stone over such plastic covers, or heel in with some soil so that it remains stable. With the darker pots, you must remove them in the sunlight the next day but with the clear plastics/glass, you can leave until fear of frost is gone. All plastic covers should have a venting hole so that it doesn't get too hot inside.
I've also used newspaper and garbage bags, but the items mentioned above were most effective. Some folks may have budding and partially leaved Japanese Maples. These should be covered with sheets if possible.
Hopefully with these methods, frost damage can be avoided. Unfortunately for fruit trees, a large tarp or cloth needs to cover the entire tree if you want to protect the bloom. This is hard to do. Many fruit groves use overhead sprinkling systems to run all night to make sure the cold air doesn't come in contact with the blossoms and leaves.
So many things we can do to try and prevent these strange springs, but thankfully, plants will recover in time.