Answer: It doesn't sound as though the flowers of your apple trees are being pollinated. All varieties of apple trees should be cross-pollinated with another apple or crabapple variety. To attain the best fruit set on apple trees, the king blossom (the largest and first one to open) in the flower cluster must be pollinated. Thus, the bloom periods of the pollinizer and the king blossom of the apple tree must overlap.
In backyard plantings, two semidwarf apple varieties that bloom at the same time should be planted within 50 feet of each other. Two dwarf apple varieties with similar bloom periods should be spaced less than 20 feet apart to ensure the transfer of pollen between trees.
Although some apple varieties, such as Lodi, Liberty, Empire, Winesap, Jonathan, Jonagold, Gala, Golden Delicious, Rome and Granny Smith may be listed as self-fruitful, they will set more fruit on an annual basis if they are cross-pollinated. Additionally, some apple varieties, such as Winesap, Stayman, Mutsu and Jonagold, produce sterile pollen and therefore cannot be used to pollinate other apple varieties. Since you don't know what your red variety is, I'm not sure it's a compatible pollinizer.
I'd recommend planting a third tree to ensure pollination of your Granny Smith. Try Fuji or Braeburn for best fruit set.
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