Common Hackberry (Celtis occidentalis)
Why would anybody be interested in a tree that is just the common variety? In this case, we Coloradoans can be very interested because “common” means it will grow just about anywhere. In our harsh country that provides a good living for people planting and replanting and pruning and re-pruning trees, the Common Hackberry is somewhat of a relief. It will grow to 7000’. Our 25 below zero winters do not bother it as it is hardy to zone 2, which helps a lot in adjusting to our sudden warm-to-cold swings. It is also not picky about soils, tolerating both acidic and our usual alkaline conditions; rocky is fine, heavy clay is OK; it really likes rich, moist, but grows right along in poor, dry, windy, polluted cities.
It is known as (one of) the fastest growing hardwood trees, growing to 40’-65’ high and almost as wide and producing very white, strong wood that stands up well to our heavy wet snows and 100 mph winds. Naturally it will do better with some care, but in my experience, if it is watered enough to live the first year, it will survive after that with no additional watering. Regular watering will make it grow a lot faster. Like a lot of young trees, the hackberry has a somewhat gangly youth; it is almost pyramidal and quite dense, then spreads with age.
The leaves are elm-like, rough and turn yellow in the fall. The hard, corky gray bark is attractive, especially in winter. The fruit is not showy, but the small, orangy-red drupe turning purplish is appreciated by the birds. Its very twiggy, dense growth also makes it good for nesting. I prefer its appearance, however, when some of this dense growth is pruned away from the trunk and larger branches. Thinning also reduces snow load as it allows the wet snow to fall through. Also it is good to shorten the branches a little if they grow too long and thin which will happen if they are watered a lot. Like most trees, it is important to remove the narrow, weak-crotched main branches when the tree is young.
In general, the Common Hackberry is a very healthy tree, but its appearance is often marred by the Hackberry nipplegall, which makes bumps on the underside of the leaves. These galls do not appear to harm the tree and in fact the psyllid insects causing them provide food for house finches, evening grosbeaks, chickadees, nuthatches, goldfinches and other species. The gall is also attacked by tiny parasitic wasps, which can be attracted by planting yarrows, dill and other umbellifers. An eriophyid mite sometimes will cause a dense twiggy growth called “witches broom” which is seldom a problem.
This xeric, rugged, medium to fast growing tree may be less suitable than some to be the main specimen in your front yard, because of the ‘warty’ leaves which can be really dramatic some years, but there are many, many other areas where the Common Hackberry will really shine– like on the west side of the house where burning, late afternoon sun and fierce westerly winds can be screened.