Scientific Name
Zelkova sinica
The zelkova genus has been known in our region for at least several decades through the species Zelkova serrata, the Japanese zelkova. It was considered a good possibility for diversifying the urban forest and has been used for that purpose in several cities in the eastern half of the U.S. but ran into some problems with our climate that were not immediately apparent. The most important issue was not surprisingly the sudden deep freezes that can occur in fall and spring. A radical temperature drop in the spring about ten years ago severely damaged many Japanese zelkovas, including some older established ones. There were also at times problems with broken limbs caused by the weight of snow when there was still foliage on the trees. The largest Japanese zelkova in Colorado, prior to those difficult weather events, lived on the Regis commons, but it failed at that time. There are currently no others of its species at Regis, but there are some that suffered little or no damage in the surrounding area, so it cannot be written off as unsuited to this region.
In 2014, Regis received a donation of a Chinese zelkova sapling from a nursery in Oklahoma, and it grew well in the Regis tree nursery for around five years. Unfortunately, about a week after it was moved to a site near the Residence Village in the spring of 2020 and began to leaf out, another one of the sudden freezes occurred. The tree not only lost its new leaves and many smaller branches, but also had severe bark splitting. Although the tree didn’t resprout during the growing season, Regis decided not to remove it, and it began to grow again the following year. At this point, despite the obvious damage one can see on the trunk, it seems to be gradually regaining a reasonable canopy.
The several zelkova species that are generally hardy in this climate do not vary greatly in leaf shape, buds, twigs, fruit, etc. The bark on many as they age is an attractive feature as it often exfoliates in patches to reveal an orange-colored bark underlayer. The jagged leaves also resemble elm leaves, though they have symmetric bases. The fall foliage color can often be an attractive mixture or yellow, orange and red. The Chinese species is one of the smallest zelkovas at maturity and may reach 30 feet in height. Often zelkovas will branch low on the trunk, and they generally show a vase-like habit as they develop. They were often recommended as a replacement for the vase-shaped elm trees that were being decimated by Dutch elm disease, but zelkovas are very resistant to that it. Being a close relative of elms, as they are part of the same botanic family, they may have some problem with elm leaf beetle infestations. At this point, we know of no other Chinese zelkovas in the region, and this tree is certainly an experiment that bears watching.