Sunday, March 24, 2013

Critical Temperatures for Fruit Buds

   Temperatures are predicted to go down to 20 to 21 F tonight and the next night.  Thankfully, the colder weather of the last few days slowed the development of fruit buds.  All the fruit trees have swollen fruit buds now, but bud development has not yet progressed to the pink stage on peaches, green tip on apples, or bud burst on pears.  If buds had progressed to those stages, the temperatures predicted would have eliminated this year's peach crop and hurt the pear crop.  
   Fruit buds are extremely cold-hardy while dormant.  Peach buds can withstand winter temperatures down to -10 F without damage, and apple and pear buds can take winter temperatures down to -20 to -30 F, depending on the variety.  Once fruit buds start to grow in spring, they progressively lose cold hardiness as they develop.  They are most vulnerable to freezes at bloom and post-bloom.
Our peach trees are thankfully still in the swollen bud stage, so the peach crop shouldn't be hurt by temperatures predicted to go down to 20 to 21 F over the next two nights.
   At the swollen bud stage where they are now, peach fruit buds would suffer about 10% bud kill if temperatures drop to 18 F, and 90% bud kill if temperatures drop to 1 F.  Apple buds at the silver tip stage would suffer about 10% bud kill if temperatures drop to 15 F, and 90% bud kill if temperatures drop to 2 F.  Pear buds at the swollen bud stage would suffer about 10% bud kill if temperatures drop to 15 F, and 90% bud kill if temperatures drop to 0 F.
   So thankfully, this freeze should not hurt our fruit crops.  We still might have frosts in the next 3 weeks that could hurt the tree fruits while they're blooming, though a light frost down to 28 F and no lower during bloom is actually beneficial, so we don't have to do so much fruit thinning.
Just a week ago we had temperatures in the 70's and were pruning peach trees.  Our son Michael helped with this while home from college on spring break, as did our other workers.
   All the small fruit crops bloom later, so aren't usually hurt by frosts.  Usually I would have removed the winter mulch from the strawberries by now, but the cold March kept new leaves from growing, and thankfully I left the mulch on the strawberries until now, which insulates the fruit buds against the cold.  The early 'Natchez' blackberries have broken bud, but the leaves grow first on blackberries and raspberries and they don't bloom until much later, usually after the frost risk has passed.
   It looks like strawberry season will start a bit later than most years, probably about May 8 or 10.  That's quite a change from last year.  We'll still have 'Enterprise' and 'GoldRush' apples for sale until early May this year.  They're protected from freezes in our sales building, and keep in top condition for 6-8 months in our cooler.  If you want to get apples (or more apples), call 620-597-2450 to let me know when you're coming.  Thanks.