To grow trees in Idaho, we need to be aware of some limitations. The first limitation is the excessive lime in our soil. When the glaciers ground up the limestone mountains north of here, we were left with a wind-blown, ground limestone deposit, in some cases 22 ft. thick. This means that we need to pick trees that are adaptable to this high ph. The second limitation is that SE Idaho is in zones 4-5. I've experimented with some zone 6 plants with some success. The third limitation is some serious pests have now moved into the area, the most notable being borers, that have made growing ash, black locust, and birches very difficult. So here are a few trees that are way under-planted in SE Idaho, but do very well here.
#1 Turkish Hazel 'Corylus colurna'
Tree Hazels can grow 6-18 in. a year and can reach 70-80 ft. tall. They are very pyramidal when young, and are shaped just like a Little Leaf Linden. Their beautiful white or tan bark and their dark green leaves make this tree really stand out. They are very adaptable to our soils and climate. They will need regular watering when young, but then become very drought tolerant. In really hot, dry years when so many trees are being scorched, the Turkish Hazels still look gorgeous. The bonus feature with this tree? It produces sweet edible hazel nuts!
#2 Chinkapin Oak 'Quercus muhlenbergi'
This adaptable tree is native to Canada, The United States, and Mexico. It grows surprisingly fast; I've had several grow over 4 ft a year. They typically reach 80 ft. tall, with the record holder being over 160 ft. It has a dainty branching habit that reminds me almost of birches. It does produce acorns, but they are small, and don't really present a clean up problem, because the squirrels haul them off as fast as they fall. Chinkapins live well over 300 years. Because, like other oaks, it has an aggressive tap root, transplanting is almost impossible, unless you buy from a reputable nursery, who propagated them in air pots. (In some future blog, we'll talk about the benefit of trees grown in air pots.)
#3 Red Flowering Chestnut 'Aesculus carnea'
This hybrid between the White Chestnut and the Red Buckeye is very beautiful! It gets the large flowers from the chestnut parent and the red color from the buckeye parent. There is a large Red Chestnut in Pocatello that has been the cause of traffic accidents. People are caught completely by surprise when they see this tree in bloom. It grows reasonably fast, up to 3 ft. a year, and doesn't scorch in the summer heat. Studies have been done on what types of flowers humming birds visit most often, and the Red Chestnut and Red Buckeyes scored very high. If you don't have room for the Red Chestnut, which can get quite large, plant Red Buckeyes, which also have the beautiful flowers but are much smaller.
#4 Yellowwood 'Cladrastis lutea'
This tree has it all! For starters, beautiful, white flowers in panicles up to 15 in. long. It also has beautiful, smooth, grey bark, very similar to a beech. The fall color is a clear yellow. It's in the pea family, so it's roots support nitrogen fixing bacteria, which improve the fertility of surrounding soil. This tree is hard to find at nurseries, but it's worth the effort! I propagate this every year with the intent to grow them larger, but they always sell out. Another tree in the pea family is Kentucky Coffee Tree, which also does very well here.
#5 Hybrid Oak 'Quercus macrocarpa x turbinella'
This little oak is a hybrid between the big bur oak that grows throughout the mid west and the little live oak that grows in Southern Utah, Arizona, and Mexico. We planted one just for fun in the outdoor smokers lounge at the old Bannock Memorial Hospital. Over the years, it has become such a beautiful tree; most people who see it think it's some kind of holly. This tree was breed by Dr. Walter Cottam at the University of Utah. This tree can be grown without any irrigation, but it looks like a small shrub. However, when it's irrigated, it becomes a beautiful tree with leathery, holly shaped leaves that stay green clear into December. It can reach up to 35 ft. tall, with a 35 ft spread.
Remember when we plant trees that are less common we increase the diversity of our plant communities and limit the risk of major pest attacks that can strike trees that are over-planted.