Early spring is a great time to think about planting new trees. If you worry that your thumb isn’t “green enough” to plant and grow a tree, start with something hardy. The USDA Plant Hardiness Zones and the Colorado State Forest Service recommends these 13 trees are recommended for Northern Colorado. Bur oak (Quercus macrocarpa) Produces acorns, fall color yellow to brown and occasionally red, very hardy and long lived Hackberry (Celtis occidentalis) Very hardy, can be susc