I have a granny smith and a yellow crisp apple tree in my back yard. This year the yellow crisp apples are completely different and have a texture and shape more like my granny smiths. Is this possibly caused by cross pollination?
Multnomah County Oregon
Thank you for your question about your apples. Apple trees, like most other fruits, may be self-fertile (they can fertilize themselves), while other apple trees must be fertilized by the pollen from another apple tree (cross-pollination.) It is generally believed that self-fertile trees' apples taste better--and set more fruit--if they are cross-pollinated. Apple trees are divided into 4 groups (1 through 4, or A through D, depending on who is doing the categorizing.)
Your Granny Smith is in flowering group 3 and it is self-fertile. I cannot find a "Yellow Crisp" variety, but Honeycrisp is in flowering group 4, and needs a pollinating partner. (You can look up the flowering group for your apple variety on the Internet, if it's something other than Honeycrisp.) I suspect that, whatever it is, is needs a partner. Here's a link to an article about pollination and apples.
And, sure enough, once the cross-pollination takes place, the "new" apples--on both trees--will start to take on the traits of the other. (When done in the greenhouse or lab, controlling for wanted traits, it's called hybridization.)
Hope this is helpful.