Blueberry shrubs are somewhat frost resistant. I have seen night-time temps dip down to 28 degrees F, while the blueberries were in bloom, and the flowers survive OK. Another plant with resistance to frost is prairie smoke, Geum triflorum. But these are the exceptions, in general, frost is damaging to flowers, and that results in less fruit, or no fruit.

Blueberries haven't opened up yet but apples plums and cherries and pears have started.

There are flower buds that are closed still, are they somewhat frost tolerant so long they hold off till frost pasts? Thanks.

This is a good resource:

Here is a link that might be useful: Critical Temperatures for fruit tree flowers

Link below is your best guide. I have found it more reliable than most of us can measure the actual temperature. In fact the amount of damage tells you how could your fruit buds experienced.

Here is a link that might be useful: illustrated spring frost thresholds

Fireweed,

You can cover your fruit tree up with a large tarp and hang a 120 V light bulb in the center. I did that a couple of nights in April and my apricots got spared from the
-24F frost.

Tony

Christmas lights work too - the C9 kind (big hot bulbs, the old style). Just be careful not to place them too close to a bloom or they could actually burn the flower.

fruitnut,

Can you explain what "old temp" means on the link you provided above?

It appears that "old temp." refers to the 30 minute damage threshold. IOW the flower/bud can withstand this temperature for durations under a half hour without fruit kill.

My apple and pear trees bear out the data from MSU as of last night when it went down to 28 in the orchard. The peach is in full bloom and appears fine as far as the petals go, don't know about the stigmas, anthers and pollen though. The bees are having a good old time in the tree today.

Golden Russet has many open blooms (maybe 20%) and they all appear fine too. Too bad GR isn't a pollen parent for Bosc pear.