2014 December 10
by Marilyn Loser
Last week I attended the Western Slope Tree Care Workshop in Grand Junction (GJ). While the presenters focused on trees suitable for Grand Junction, there were some that might be appropriate for Alamosa. Alamosa is much colder and higher than GJ. I consider our United States Department of Agriculture Plant Hardiness Zone to be 3 since many of our record lows for January are below -30 degrees Fahrenheit (all temperatures listed are in degrees F).
Is Alamosa generally on a warming trend? I don’t know. We had a record low of -32 on January 15 last year. The only other record low this century was -32 on January 17, 2008. With the exception of 6 record lows (ranging from -27 to -34) in January 1984, all other record lows were before the 1980’s.
Would one cold night kill a Zone 4 (-20 to -30) tree? Again, I don’t know. Typically, by January our trees are dormant and a short cold spell might not be too hard on them.
I’m hoping any readers that have had experience with the trees listed below will let me know since I don’t know of any specimens in our area.
Dr. Mike Kuhns, Utah State University Extension Forester, gave a talk on Trees for Western Colorado. He lists Ginkgos (Ginkgo biloba) as being in Z3 while the Denver Street Tree Guide (DSTG) lists it as Z4. Also known as Maidenhair Tree, it has distinctive fan shaped leaves and is considered a “living fossil” according to the Colorado Tree Coalition (CTC) website. Its origin dates back more than 170 million years ago when the dinosaurs roamed!
“Once widespread in Europe and North America, most died out during the Ice Age,” reports the CTC. “Surviving trees were found in China. If it were not for their preservation by Buddhist Monks, the trees would likely have gone extinct. None exist in a wild state.”
I am fascinated by this tree! They line the streets in Santiago, Chile, and I loved seeing them. If you purchase one, make sure it is a male! The females produce messy fruit that stinks. Some cultivars are slow growers. Randy Coleman, Forestry Crew Leader – Grand Junction Parks and Recreation, has one specimen that is growing very slowly.
European Larch (Larix decidua) is another A3 tree Kuhns suggested. It does like acidic soil (Alamosa’s natural soil is alkaline). Unlike most conifers, it drops its needles in the winter. There are no significant diseases of larches in Colorado according to CTC.
I had never heard of the Amur Corktree (Phellodendron amurense) recommended by Kuhns. Again, he lists Z3 while the DSTG says Z4. It has glossy dark green leaves that turn bronze-yellow in autumn. It needs a large root space. Kuhns says to plant males to avoid the messy fruit and that it tolerates a wide range of soil and other site conditions. He mentioned that if “Amur” is in the name, the species probably originated in a cold climate.
White Oak (Quercus alba - ZE) was on Kuhns’ list, but he didn’t talk about it during the workshop. It prefers full sun and likes moist, well-drained, acidic soils (according to the CTC) so I’m not sure why he would suggest it for a fairly dry environment like GJ. Again, I wonder if anyone knows of one around town.
Have you ever seen a Japanese Tree Lilac (Syringa reticulate – Z3)? I’m a big fan of lilacs and would like to try a tree shaped species. According to the DSTG, its mature size is 25’ by 20’ and it has creamy white blossoms in the spring. The guide notes that it “leafs out early and frequently suffers frost damage in spring.” Perhaps this isn’t a good selection for Alamosa since we can have some nasty spring frosts.
Several other Z4 trees were discussed during the workshop. They might be worth a try. Coleman let a walk through GJ’s beautifully landscaped downtown shopping park. He says he likes “Sensation” Box Elder (Acer negundo – Z4) as a street and park tree. There are a few mature box elders in Alamosa’s downtown residential area, but I don’t know what variety they are. “Boxelder trees are usually very tolerant of temperature extremes, drought and high pH (alkaline) soils,” says the CTC. “Sensation is a male tree and not very attractive to the boxelder bug.”
I’ll continue this topic in a future column. Please write me at Marilyn@AlamosaTrees.net if you have any information on these trees.