Answer: There are lots of variables with plants and lots of confusing cultivars. If the plant tag says it will grow 2-3' wide then you probably have the Pyramidalis cultivar. These plants truly do grow tall and narrow and are great for privacy hedges. The Emerald Green Arborvitae species grows 8 feet wide. If you have the narrow growing arborvitae, plant them 3 feet apart and they will grow into a nice thick hedge. As for amending your native soil with compost or other organic matter, the jury is still out on the advantages of doing so. While mixing organic matter into the soil will help it drain quickly and make for a nice, rich planting spot, the roots of your arborvitaes may not want to venture out into the native soil if you only amend the planting hole. If you amend a large area with organic matter rather than just the planting hole, you will encourage the roots to spread out and grow well. So if you're you are going to amend the native soil, be sure to do an entire planting bed, not just the planting hole. Hope this clarifies things.
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