A blueberry bush is dormant during winter when you see no swelling of the buds.
Fruit buds at the end of the branches will begin to swell, but still tolerate freezing temperatures up to 20 degrees Fahrenheit. Soon after, leaf buds will begin to emerge farther down on the stem.
Blueberry bushes are in full bloom when most of the blooms are open. The blooms can tolerate temperatures of up to 31 degrees Fahrenheit.
When the blossom petals fall off, you will see the first green fruit. This stage can be damaged by frost.
A scattering of fruit are bright blue and ready to harvest by hand.
Entire clusters of fruit are ready to pick. This harvest is often done by machine.