Trees are like people. Some are fat. Some are skinny. Some are tall. Others are short. But unlike people, we can usually predict what shape a tree will become when mature, which is a real advantage for those of us who select trees for specific locations.
Selecting trees that fit the available space also makes good sense – both in common sense and dollars. Trees that stay narrow in a narrow location, or short under overhead wires, reduce the potential for future interference and thus reduces the need for repeated pruning. Dollars can then go towards more planting instead of costly maintenance.
Visualizing the ultimate mature size and growth characteristics of a tree is very difficult for the inexperienced consumer. In addition, trees have different branch patterns and characteristics. Some branches are smooth and stout, like most Mountain Ash and Horsechestnut. Others are irregular and twiggy, such as some Locust and Serviceberry. Their growth and branch pattern may also dictate the necessity and/or frequency of future corrective pruning, to maintain desirable shape and density. Mountain Ash and Karpick Maples seem to need little corrective pruning, whereas the serviceberry and crabapples may push early branches in all directions, as well as periodic sucker growth. These tendencies are not only related to final size and shape, but also the cost and time in maintaining that shape.
What we need is more useful information on how the many varieties perform, especially the new ones. The following are ten trees that appear to fit the limited space category. These ten are just a scratch at the surface of what is available. This information comes from nursery catalogs, tree lists, textbooks, and a lot of hearsay and experience.
1. Sorbus tianshanica, Red Cascade Mountain Ash (according to Jacobson, this is a clone of Sorbus americana or Sorbus americana ‘Dwarfcrown’).
Grows to 20 ft. x 8 ft. wide, with white spring flowers turning to orange-red fruit. Green pinnately compound leaves turn yellow in fall. We have found this tree to be easy to grow, transplant, prune, and care for. It is straight and narrow with stout twigs, and performs very well in tough street locations. We have seen no insect or disease problems. As far as messy fruit, the birds strip the tree of its berries before they ever reach the ground. This is a carefree tree. Zone 3.
2. Amelanchier x grandiflora ‘Autumn Brilliance’, Autumn Brilliance Serviceberry.
Mature height is 20 ft. x 15 ft. wide. It has small white flowers that become small, almost insignificant black berries. The clean serviceberry-like leaves turn shades of apricot to brilliant red in fall. This serviceberry is especially nice in tree form, with limbs starting at about 5ft. to 6 ft.; excellent as a street or landscape tree. It has been found to be less susceptible to rust in Washington State. This tree is less twiggy early, becoming more twiggy and dense as it matures. Zone 4.
3. Acer platanoides ‘Crimson Sentry’, Crimson Sentry Norway Maple.
Mature height is 25 ft. x 15 ft. wide. Like its parent, the Crimson King, this Norway Maple has deep, dark purple leaves from emergence to fall, when it can actually turn a slight golden yellow. But its limited height and narrow form makes this a real gem in certain locations. Although it is grown primarily with lower limbs, try to find nursery grown trees limbed up to 5 ft. or 6 ft. minimum for street tree locations. Internal twig and branch growth can become dense and crowded, so careful thinning is beneficial early in its life. Its’ most limiting drawback is its’ susceptibility to Powdery Mildew in some locations. Zone 4b.
4. Malus ‘Sutyzam’, Sugar Tyme Flowering Crab.
Mature height is 18 ft. x 15 ft. wide with very clean green foliage and white spring flowers. Fruit is small, about 1/2”, red, and persistent. Sugar Tyme can be pruned up relatively high for street tree use and appears to be tolerant of urban conditions. The Washington State Experimental Station in Mount Vernon, Washington found this tree to be very resistant to most of the crab apple diseases. It is also an easy one to transplant. Zone 4.
5. Malus ‘Prairifire’, Prairifire Flowering Crabapple.
Mature height 20 ft. x 20 ft. wide with an upright spreading shape. But most important, this is a clean crab, considered excellent in all categories of disease resistance. This is the cleanest of all the bright pinkish red flowered crab apples that I know of. The foliage is purple, then turns a reddish green. The fruit is small, 3/8 to 1/2” diameter. This tree may prove harder to buy because of its popularity, as well as difficulty in maintaining good branch structure during early production. Zone 4.
6. Acer rubrum ‘Karpick’, Karpick Red Maple.
Mature height 40 ft. x 20 ft. wide. Has the size of an Armstrong Red Maple, but has a more defined central leader and smaller lateral branches. It is also more uniform in its shape. The leaves are more deeply cut and pointed than the Bowhall Maple; and therefore, give it a finer texture. Typical green maple leaves turn yellow to orange-red in fall. This tree has shown to be tolerant of poor drainage and tough urban conditions. Zone 4.
7. Pyrus calleryana ‘Chanticleer’ or ‘Cleveland Select’, Chanticleer or Cleveland Select Flowering Pear.
Mature height is 40 ft. x 15 ft. wide. This tree is probably one of the most popular trees in the country, which accounts for its recent scarce availability. Clusters of flowers cover the tree in spring, followed by glossy, green leaves. Then the leaves turn a purplish red in fall. It is somewhat tolerant of poor drainage and urban conditions, resistant to fireblight, and much less susceptible to wind breakage than the ‘Bradford’. It is relatively easy to grow, transplant, and maintain. Zone 4.
8. Robinia pseudoacacia ‘Bessoniana’, Bessoniana Black Locust.
Grows to about 30 ft. tall by 20 ft. wide. Has medium green foliage with clusters of white flowers. Fall color is yellow. This may be one of the better small street trees for under power lines in tough, dry locations, especially on the east side of the mountains. It is compact, round headed, and usually spineless, with a clean balanced appearance and well-developed central leader. Zone 4.
9. Fraxinus excelsior ‘Globosa’, Globe Ash.
This 20 ft. x 20 ft. tree grows in a neat, dense, and formal globe shape with medium leaves and stout twigs with black fuzzy buds. This shape is maintained with little or no corrective pruning. The grafted crown expands very slowly on a 6 or 7 ft. standard trunk into the shape of a lollipop. They remind me of “Truffula Trees” in reference to Dr. Seuss’s trees in “The Lorax”. Leaves stay green late, then turn yellow and drop quickly. This is a sharp tree for outside malls, gardens, and formal entrances. This should become a very popular tree. Zone 3.
10. Acer truncatum x A. platanoides ‘Warrenred’, Pacific Sunset Maple.
Grows to a height of 30 ft. x 25 ft. wide. This is a tough mid-size maple tree that is great for under high power lines, as well as other landscapes. It has the upright spreading, rounded crown with dark green, very smooth glossy foliage that changes to hues of yellow and orange-red in the fall. Considering its Norway Maple ancestry, I suspect it possesses those tough Norway Maple characteristics. This tree has a bright future! Zone 4b.