I planted 2 carpathian english walnut trees about 12 yrs ago & about 20 feet apart. They started about knee high. One tree is about 15 feet now & the other is only about 10 feet tall. The problem is that they are not blooming at all yet. All they have done so far, is growing very slowly. They do look healthy ok. The goal was that we would have some walnut's by now.....Any idea's ??