frost damage to fruiting trees' blossom - at what stage?

Are tree fruit blossoms eg gage, plum, pear, apple susceptible to frost damage right from flower bud opening to fruit development, just at a particular stage or is it a big depends?
I'm asking as tonight and tomorrow we are forecast a frost and my Golden gage tree has been in full bloom for a couple of weeks . Last week I covered the tree in horticultural fleece but we have heavy rain now and am feared a soggy weight of fleece might do more harm than good and it made me question what is it that gets damaged.

thanks
Cesca

Try this:

Critical Temperatures for Frost Damage on Fruit Trees - https://extension.usu.edu/files/publications/factsheet/pub__5191779.pdf

it's a table for light and severa damage temperature for various fruit trees - apple, pear, apricot, cherry, peach, plum - at different stages of flower bud development up to the full blossom.

If you need the temps in C, just go to Google and type in for example: 2 F in C

The flowers getting rained on might actually help as the process of conversion of liquid water to ice actually acts as a buffer - as long as ice is still forming the temperature will stay at 0 C, not below. That's why spraying with water is actually used on purpose in case of frost warnings - http://fruitgrowersnews.com/article/protecting-your-fruit-from-frost-and-freeze/

excellent information, thankyou

Well then... We just had a -25 F / -4 C night after all the various fruit trees have already set fruit (except quince but blossoms being hit instead of fruits is not really any better). I guess only the hardcore will survive - haskap, juneberry, aronia, seabuckthorn. Grapes were setting flowers. Black locust also. If that got wiped out (it sure looked sad in the morning) first super bee forage will be pumpkins in June.

my sympathies to you and the bees! I've about thrown the towel in trying to fleece and/or spray the trees, we've had a few -2C.
Just bought myself a lonicera caerula (had to look up what haskap was) so good to hear the blossom on that are hardy? You've got seabuckthorn and aronia flowering now?

Just came back after having had to do some other stuff elsewhere.

The orchard looks, well, apocalyptic.

- Anything green has been entirely burnt off on grapevines, mulberries, sweet chestnuts, kiwis (arguta), black and honey locusts, paulownia, koelreuteria. Evodia and buddleia only partly but still a horror to look at.
- Apricot leaves don't look as cooked as the ones above but are limp and fruits have split.
- Fruit on sweet cherries and pears has wrinkled and is turning black.

I don't think I've seen such destruction since starting the orchard 8 years ago. Spring was quite early, everything was going full steam ahead and this was a really brutal interruption. I'm not even sure that the youngest plants will survive. Very very sorry so see this since the fruit set was excellent and we were very much looking forward to having the first really abundant harvest.

On to the possible survivors...

- Gooseberries and currants look fine at the moment but not sure if that just means the damage hasn't shown yet.
- Plum and apple trees look sad (like me) but relatively fine. Ditto quince. Might get some fruit there. Some of the apple varieties are quite late to come into leaf/flower (Winterrambour, Rote Sternreinette).
- Peach trees look suspiciously fine - I don't really expect the fruit to survive. The varieties we have are supposed to be more robust than the average but this was brutal.
- Aronia is in flower and is supposed to be quite hardy. Haskaps should be VERY hardy as they can normally even start flowering at below-freezing temps (they have already finished). Seaberries might be OK. Juneberries (amelanchier) also.
- Raspberries were developing flower buds but I think that even if they were hurt they will regrow and set new buds - we have the everbearing Autumn bliss.

Rain is now forecast followed by another frosty night Wed/Thurs. Chuck Norris might possibly survive after this second wave.

There will be no black locust for the bees this year -- and that's usually the main flow. Crimson clover looks relatively OK and might even be of use to them. Oilseed rape was in full flower when the frost hit but it's in the cabbage family so dunno. The first strong flow that I really expect to be possible in the remainder of the year is from pumpkins and that's mid-June.

Crt Jakhel wrote:Well then... We just had a -25 F / -4 C night after all the various fruit trees have already set fruit (except quince but blossoms being hit instead of fruits is not really any better). I guess only the hardcore will survive - haskap, juneberry, aronia, seabuckthorn. Grapes were setting flowers. Black locust also. If that got wiped out (it sure looked sad in the morning) first super bee forage will be pumpkins in June.

And... Again

Spring came 2 weeks early vs. the average (measuring by flowering times of early trees) in the previous year. It came 3 weeks early this year and it seemed for a while that we might not have to pay the bill for that. It did come though, same as before. Even the overnight temperature was the same. Threw an impromptu hallooween party (young trees all clad in white) but didn't seem to make a difference.

Some lessons from the previous year:

- yes, the black locust definitely gets wiped out - if we're really lucky the tops of oldest, tallest trees will still be in flower
- soft fruit will still bear a crop - although smaller
- the flowers of elaeagnus umbellata/multiflora can take -25 F / -4 C - (don't know how much more but so far, so good) - the bees keep going at them and in the fall berries form normally
- bees can be suported by buckwheat during the summer but the loss of main flow does have an impact on how the hives develop and what level of mite problems can be expected
- crimson clover did indeed survive, started to flower and helped the bees during May in the absence of locust

Are you prepared for late frosts?  

Do you have any other insights for how to protect blossoms and developing fruits from freezes in their early stages?  

Bumping this topic to help people get more fruits this year..  

This is a good topic to bump up right now. I have a couple of strategies to deal with frost and cold weather this time of year.

Years ago, I read that spraying seaweed extract can prevent frost damage. Apparently, compounds found in seaweed extract such as  betaines and cytokinins help protect plants from frost damage. The potassium that is found in seaweed extract can also protect plants. Check out this article:

https://deepgreenpermaculture.com/2022/01/17/how-to-protect-plants-from-frost-with-seaweed-extract/

A foliar application of seaweed extract will give plants 2-3 C. degrees of protection for 10-12 days. I use Maxicrop or Neptune's Harvest.

Another thing I do when cold weather persists into the flowering period for certain trees and no bees are to be  seen is to hand pollinate trees with an old paint brush. I just go from tree to tree brushing the flowers. I sometimes hand pollinate my favorite apricots, peaches/nectarines and  Japanese plums/pluots this way. I think this really helps set more fruit when we have a cold, wet spring like this year.