I live in Iowa and I recently purchased 2 semi dwarf Liberty apple trees and 1 semi dwarf Wolf River apple tree. They are planted about 150 feet away from another apple tree that I have (the house I moved into had 3 apple trees and 2 pear trees) do I need to purchase another tree for them to pollinate with or will they be good on their own? I'm new to working with Apple trees and am eager to learn. Thank you.