Small Trees for Eastern or Northern Exposures

Shade trees 40’-60’ high and wide are great on the south and west sides of our houses and offices. They reduce temperatures and reduce cooling costs in the warm months, but they are not always appropriate. We don’t want dense shade where we grow most xeriscapes, rock gardens, herb gardens, most natives and many perennials. In addition, there is no need for big shade trees on the north side, and the morning sun is usually welcome on the east side of our houses and workplaces. And many plants prosper in morning sun and afternoon shade. It is also significant that a 20’ tree costs far less to have pruned than a 40’ tree. So it seems to me we should be growing small trees under 30’ tall on the east and north sides of our buildings.

         Here are some examples of trees 15’-30’ high and wide that will perform well on most eastern and northern exposures that are not heavily shaded by big trees or very large structures:

         Ginnala Maple, Acer ginnala, is a tough little tree from the Amur region of Manchuria. It is fairly well-known but often not well grown. Sprawling and broken specimens and yellowing chlorotic leaves give this tree an unnecessarily bad image. Although Ginnala Maple can be grown as a single trunk tree, it has a tendency toward multi-trunked forms. A single trunk has a natural balance and stability. The problem with many trunks is that they lean away from each other for light, making them vulnerable to snow load damage. The solution is to limit the number of trunks to 2 or 3, shorten lanky branches 10%-20%, and remove branches that are making weak crotches. When these corrections have been made, Amur Maple will be a very attractive and dependable tree growing to 15’-25’ in full sun or part shade. The three-lobed leaves are attractive and provide a glorious display of red and orange fall color. The surprisingly fragrant little flowers mature into winged seed capsules (samaras) that turn from chartreuse to reddish green or bright red. This is a very drought tolerant tree that only needs watering once a week or less. It is very cold hardy and has no serious pest problems.

         To avoid the problem of the yellowing iron deficiency known as chlorosis, avoid planting in highly alkaline soils or you can amend yearly with sulfur and iron. The common cultivars are ‘Flame’ with flaming red fall color and red samaras; and ‘Compactum’ also with good red fall color and growing to a petite 6’-10’ high. Because these forms of Ginnala Maple are hardy to zone 3 or 8500’, they can be artfully pruned to be long-lived substitutes for zone 5-6 Japanese Maples.

         Another smaller maple that does well in Colorado, but tolerates our alkaline soils better than Ginnala Maple is Tatarian Maple. This 20’-25’ tree can be bushy or single trunked and makes a handsome specimen. The fall color is yellow or reddish and the winged seed heads are rosy-red. The selection ‘Hot Wings” found by Ft. Collins Wholesale Nursery has really red samaras that are as showy as flowers and persist for a long season. It has red with yellow fall color and the branching structure is stronger than the species. Tatarian Maple, Acer tataricum, is very hardy to zone 3 and can grow in drier conditions, though will do better and grow faster with one good watering a week.

         Many hawthorns are superior small trees for Colorado, thriving in our alkaline clays and even tolerating drought.  Toba Hawthorn (Crataegus x mordenensis ‘Toba’) is a hybrid with our native Craetagus succulenta. It grows 15’-20’ with a beautiful rounded form. The double white flowers are held in small bouquet-like clusters and fade to an attractive pink.They are said to be fragrant while other hawthorns are “malodorous”, and the thorns are few or absent. The red fruits are 3/8” and are not messy, but do not persist long. The fall color is yellow to orange. Toba Hawthorn is very cold hardy to zone 3, resistant to rust and is quite drought tolerant. My still small specimen has been growing bravely on the south side of our herb meadow where it is only occasionally watered, and still it blooms, fruits, and gets stronger every year.

         Another good hawthorn for an eastern or northern location in Colorado is the Thornless Cockspur Hawthorn.  Whereas the species C. crus-galli has 2” long thorns, C. curs-galli inermis is thornless and grows to 15’-25’. The single white flowers bloom in flat-topped clusters with a slightly unpleasant odor for a week, then form half inch bright red berries that persists into winter. The fall color is often a beautiful orange-red. The horizontal branching and glossy, dark green foliage add to the ornamental effect. It is hardy to zone 3 or 4, is generally healthy in Colorado and resistant to aphids.

 Eastern Redbud, Cercis canadensis, says woody plant expert Michael Dirr, “…has no equal among small flowering landscape trees.” And because it blooms so early, before the leaves have unfurled, and because the color of the pea-like flower is a bright violet, it is as welcome in spring as the reddest tulip. It has a reputation for being fragile and for needing protection here in Colorado. One local catalogue says to plant it in filtered shade to shade, but the 25’ specimen at our house is on the south side of the house and is successfully shading our bay window.

  Because Eastern Redbud succeeds in a wide range, hardiness of individual trees is dependent on the seed source, so it is important to buy a tree grown from a local or northern seed source. I have noticed many self-sown seedlings that are quite tough, but also have heard reports of Redbuds dying to the ground. Gary Epstein, of Ft. Collins Wholesale Nursery, told me that when a Redbud dies back a year or two after it was planted, we should select the best sucker from the root and let it grow, and if it dies back the next winter, again select the best sucker and cultivate it. In this way a bigger root system will eventually support a tree which will then get big and live for years.

         Redbud has beautiful heart-shaped leaves. The branches  have a tendency to make narrow crotches, and these co-dominant stems can easily split, so it is wise to select the stronger or best-placed of the two branches and remove the other in order to have a strong framework. It has no disease or insect problems, but seedlings need to be weeded. It is common to find round “bites” taken from the leaf-edges. These are cut-outs made by leaf-cutter bees that are important native pollinators and should be cheerfully tolerated. Redbuds can grow 15’ or 30’ and can develop great character after many years.

Wafer-Ash or Hoptree (Ptelea trifoliata) is a native of the eastern and southwestern US, including Colorado where it is found mostly on dry hills and canyons. It is a unique small tree or big shrub, growing fairly slowly to 15’ or 20’. The three-parted leaves are dark green, very glossy, and turn bright lemon yellow in autumn, often falling all at once and creating a dramatic effect under the tree. Wafer-Ash bears clusters of vanilla-scented greenish-white flowers in May. The “wafers” are the flat, elm-like seeds that can be one inch in diameter and are showy. It is drought tolerant, but mine has taken 15 years to reach ten feet, under very xeric conditions, and is now a handsome specimen. It has no serious pests or diseases, and can grow in full sun or full shade. Its lovely branching structure and dark brown bark make it very attractive in winter.

Apricot, Prunus armeniacum, makes a very good small tree 20’-25’ high and wide, that is very long-lived for a Prunus. White flowers appear in very early spring and are very attractive to honeybees and the occasional hummingbird. Although fruit is a rarity, it is well worth growing. The bark is attractive and the wood is stronger, and so it breaks less than peach or cherry. The fall foliage is gold with some reddish coloration. Apricot is winter hardy and quite tolerant of xeriscape conditions.

There are many bird-fruit and people-fruit trees that do well with an eastern exposure, and a northern exposure can be beneficial if there is enough light. A fruit tree on the north side of a building or evergreen tree will be protected from the winter sun and will be less likely to be coaxed out of dormancy by early warm temperatures, only to have its blossoms frozen. This of particular benefit to apricots and peaches, but can be helpful to other fruits as well.

Apples and Flowering Crabapples are very good small trees for Colorado growing from 12’ to 30’ high and wide. In general, trees grafted onto dwarf rootstalks are weak and vulnerable to diseases, drought and blow-over. Semi-dwarfs are also weaker, but are successful with good care. The flowers can be white or shades of pink or deep pink and are sweetly fragrant, attracting and feeding honeybees. The fruits, of course, can be good to eat or purely ornamental. Crabapple fruits that are smaller and persist into winter provide a long season of ornament without a mess. Apples and crabapples have very strong wood and if pruned occasionally, will have little storm damage. They can be very long lived.

Fireblight is a very serious bacterial disease which affects apples and flowering crabapples. Therefore it is important to select varieties know to have good resistance to fireblight. Some apples with fireblight resistance are: Haralson, Sweet 16, Cortland, Liberty, Red and Yellow Delicious, and Honeycrisp. Some flowering crabapples with resistance to fireblight are: Brandywine, Centurion, Coral Burst, David, Dolgo, Indian Summer, Profusion and Thunderchild.

Another great small tree is European Mt. Ash. Sorbus aucuparia ‘Michred’ is a smaller (20’-25’) selection that is more resistant to fireblight than the species. This is a beautiful ornamental tree with dependable white flowers, brilliant red fruit and glorious fall colors, combining red, gold and orange with plum and russet. True, the flower fragrance is not delightful, but the long season of interest is well worth it. The compound leaves give a fine-textured look and the growth is upright. It is also a favorite fruit of many birds. It was a sacred tree to the ancient Druids who claimed that eating the fruits would give a man the strength of ten men. Of course I had to try it and found that it takes the strength of ten men to eat them.

These small trees may only create limited shade, but they still give altitude and can define spaces. They also make protected microclimates without depriving plants of too much sunlight. In addition, artistic pruning can make them into sculptural elements that fit well into small spaces. They can provide structural beauty in seasons when flowers are not putting on a big display, and they can make a screen without blocking as much view.