I'm thinking about planting some Aspens out front. We're at about 8,500 alt. in Woodland Park. We don't have a lawn but do have some large ponderosa pines. I saw some Aspens at HD for sale at a reasonable price. They had three trunks in each container. It did look as though the tops might have been trimmed which made me wonder if that would impact their growth? Also if I were to purchase several of these, what sort of spacing do I need to use?