Garden

[depglass]

We have a Honey Crisp and a Zestar planted outside the kitchen window.  They are several years old and last year we got a few blossoms on the Zestar only.  First time and we've never had blossoms on the Honey Crisp. I know there are male and female squash plants, but asking neighbors for help with why we are having problems brings out ignorance on the love life of trees.  

[gardenman]

Apple trees have both male and female flower parts on the same tree, but need pollen from a different tree to set fruit. If a neighbor has a different tree the bees might pollinate your trees even if you only have one tree in flower. The bees can bring you the foreign pollen needed from a neighboring yard. It's easier if you have two flowering trees at once.

[JustJazzmom]

And if in the neighborhood there is a crabapple tree in bloom, the pollen from that can fertilize the 2 apple trees you have. 

It's an old farmer's trick to put a flowering branch from one apple tree and put it into another apple tree to get fruit.

As gardenman said, you need 2 varieties of apple trees for each to set fruit.