columnar apples trees not blooming
What would prevent healthy columnar apples trees from blooming? I have 5 columnar apple trees planted about 7 years ago that have never bloomed. Each year the foliage is thick and green. The trees always appear to be very healthy. I fertilized in early years and have since stopped. They are all planted in a mulched bed, and are on a slight slope. Three are Red North Pole and two are Golden Sentinel. They receive at least 5-6 hours full sunlight in their location. Following advice of an article two years ago, I tried the shoveling down around the base of the trees to cut through the roots with no effect. I have pruned very lightly in winter to remove branches at bottom and to keep a good shape. At this point, should I just remove these and try different type? Thanks for any information someone may have.
Here is a link to a very interesting extension article on why apple trees don't bloom (refer to page one)- it has great insight and provides many ideas to try: