Ornamental trees have some feature, such as flowers or colorful foliage, that makes them distinct. In Minnesota, trees must tolerate a harsh winter, so they must be hardy to USDA Zone 3. Five trees that are not appropriate as ornamentals are considered an invasive species by the Minnesota Department of Natural Resources: Norway maple (Acer platanoides), Amur maple (Acer ginnala), Russian olive (Elaeagnus angustifolia), Siberian elm (Ulmus pumila), and Siberian peashrub (Caragana arborescens).
Crabapple (Malus) trees grow between 7 and 20 feet high, with a spread of between 12 and 30 feet. They produce red, pink or white flowers in the spring. Leaves vary in shades of green, purple and red. Not all are hardy to Zone 3, but varieties that are include Flame, Radiant, Sparkler, Vanguard, Red Splendor, Royalty and Snowdrift. Pink Spires and Selkirk varieties are hardy to Zone 2. Plant flowering crabapples in full sun in well-draining, loamy soil.
Red maples (Acer rubrum) average from about 50 to 75 feet high with a 25- to 45-foot spread. They are adaptable to different soils and moisture levels. The name comes from their brilliant fall color, which can be red, yellow or orange. Varieties that grow well in Minnesota include Autumn Spire, Firefall (TM), Freeman and Northwood.
The Autumn Splendor version of the buckeye (Aesculus) is a good choice for Minnesota. It grows about 35 feet high and produces clusters of yellow flowers in the late spring, followed by a fruit that is similar to a horse chestnut. It has shiny green leaves that turn bright maroon in the fall.
Flowering plum (Prunus americana) and almond trees (Prunus glandulosa) won't always produce fruit, but the attractive flowers and fall color make up for this small factor. It grows about 20 feet high, with a spread of between 15 and 20 feet. The Newport variety has pink flowers and dark purple leaves. Princess Kay produces a white double blossom with leaves that turn red in the fall. Manitou produces pink flowers and is a hybrid almond tree.
Corktrees and Coffeetrees
The corktree (Phellodendron amurense) and Kentucky coffeetree (Gymnocladus dioicus) are trees that add interest even in the winter because of their deeply furrowed bark. The Corktree is fast-growing, with an average height of 40 feet and a similar width. It tolerates alkaline soils and resists most insects and diseases. A good variety for Minnesota is His Majesty. The Coffeetree grows about 50 feet high with a 50-foot spread, and tolerates a wide variety of soils. Best of all, it is easy to grow grass under it and it has no seed pods. A good variety for Minnesota is Stately Manor.
The Minnesota variety of redbud (Cercis canadensis) is a good choice for anyone needing a smaller ornamental tree. It grows about 12 feet high, with a similar spread. It produces dark pink to purple flowers in early May.
Two ornamental pine trees that grow well in Minnesota include the jack pine (Pinus banksiana) and red pine (Pinus resinosa). The Uncle Fogey variety of the jack pine grows about 6 feet high and has a drooping habit. The Wissota variety of the red pine is a dwarf form of Minnesota's state tree---which in its original form has been to known to reach 100 feet tall. The dwarf form reaches a height of 6 feet.
A few more trees that you can consider are Amur Maackia (Maackia amurensis "Summertime"), Double Flowering Plum (Prunus triloba), European Mountain Ash (Sorbus aucuparia "Michred"), Japanese Tree Lilac (Syringa reticulata), Magnolia x Jane (Magnolia x Jane), Pagoda Dogwood (Cornus alternifolia), Paper Birch (Betula papyrifera), Russian Olive (Elaeagnus angustifolia), Showy Mountain Ash (Sorbus decora), Viburnum Nanyberry Tree (Viburnum lentago) and Walker Weeping Caragana (Caragana arborescens "Walker").