My cherries all fell off of the tree?
This is the second year in a row, where all of a sudden, ALL of the small developing cherries fell off of the tree, and did so in a single day. What the heck? The tree is healthy otherwise. No signs of bugs. The tree was laden with small (Olive size) cherries, some already turning a little pink. The tree is a grafted type with four different varieties of sweet dark fruit. Please help.
Multnomah County Oregon cherry trees
Thank you for your question about your cherry tree. There are several reasons that cherries drop prematurely from trees before fully ripening. Different varieties have to cope with different problems, so it would be helpful to know exactly which have been grafted onto the trunk or branch.
But here are some typical factors: (1) for cherries that are not self-pollinating, there may have been a lack of pollinators, and the cherries that are there aren't capable of producing a seed (the 'pit,' the plant's objective). (2) Your soil may lack sufficient nutrients, which you can measure by having your soil tested, both for nutrients and for pH. (3) There may be a severe carbohydrate stress when there has been insufficient sun and heat due to cool, cloudy weather. This weather phenomenon also limits the activity of pollinators such as bees, which are declining for a variety of other reasons. (4) There may have been a frost during the bloom. And (5) your tree may need to be pruned so there are adequate resources (water, nutrients, sunlight) which can be remedied by pruning while the tree is dormant to open up the branches (and, therefore, the leaves) to more sunlight. Here is a link to an OSU Extension article about pruning.
Cherry trees, like other trees, are often afflicted with insect infestations and fungal infections, but if your tree looks otherwise healthy, there is nothing from which either of these might be diagnosed. If you see leaf or bud anomalies, please photograph and write back.
I'm sorry there's not just one clear answer to the problem, but soil testing and pruning are really the only things over which you have any control. Good luck!
My reply to the expert: soil pH is 7.0, I fertilize quarterly with a light dose of 16-16-16, and there are both Orchard Mason and honeybee nests within 50 feet. The trees have been properly trimmed and were sprayed with dormant spray on early February. What am I missing? No sign of pests
A couple of other resources that deficiencies of boron and zinc might be an issue (although that seems likely in clay soil), that too little sunlight (less than 8 to 10 hours a day), and an inappropriate fertilizer ratio might also impact cherry tree fruit drop. Specifically, rather than the 16-16-16 (which is equal parts nitrogen, phosphorus and potassium), you should be using a 5-10-10 mixture. (Nitrogen promotes leaves; phosphorus promotes roots and potassium promotes flowers, fruits and seeds.)
You can't control for weather or sunlight, but a soil test might get you answers about the issues you can.