Crabapples are one of the most desirable small trees to incorporate into today’s smaller landscapes. They are easy to grow in zones 3 through 7, have a dramatic spring floral display, tolerate a wide range of soil and climatic conditions, and are readily available. However, they are often mislabeled, have messy fruit, have problems with the understock, and are frequently susceptible to a number of diseases that can make them aesthetically unattractive.
In an effort to select the most trouble free and aesthetically pleasing crabapple cultivars, evaluations were made at 25 test sites ranging from Canada to Mexico and from coast to coast. Grown at these test sites were 50 of the more desirable cultivars selected from the list of 1,000+ available cultivars. All of the crabapple cultivars were grown on common rootstock. Each cultivar was evaluated based on: disease resistance, form, and flowering and fruiting characteristics.
Apple scab, caused by the fungus Venturia inaequalis, favored by high humidity, is a serious disease. It causes spotting on leave and fruit that often result in premature and permanent defoliation of trees by mid-summer.
Apple scab can be controlled with fungicides.
Fire blight, caused by the bacterium Erwinia amylovora, doesn’t occur as often as apple scab, but can cause dieback or death of crabapple trees. Infected issue appears to have been scorched by fire. The bacteria which causes fire blight thrives in warm, humid weather and is spread by insects.
Cedar apple rust, usually caused by the fungus, Gymnosporangium juniperivirginae, is a less serious problem and mostly affects leaves and fruit of native species, Malus ioensis and M. coronaria. It is active only in those areas where its alternative host, eastern red cedar, Juniperus virginian, is found.
Powdery mildew is caused by several fungi, including Odium pyrinum, Phyllactinia corylea, Posdosphaera leucotrica, and P. oxycanthae. Infected leaves become cupped and are covered with a white powdery coating. Poor air circulation and temperatures around 70º F provide ideal conditions for the growth of powdery mildew.
With over 1000 different cultivars to choose from, it is possible to have crabapples that are shrub-like, weeping, upright rounded, spreading, etc. The crabapple cultivars selected will depend upon garden size, planting site, and adjacent plants.
Fruit size varies from 1/4 inch to more than two inches in diameter. Larger than two inches in diameter, are no longer considered crabapples. Fruit color may be yellow, orange, or red, with bright red being the preferred color. Cultivars have been selected for fruit that persists well into the winter. Since fruiting occurs only when the crabapples bloom, some cultivars fruit on alternate years while others fruit every year.
Since crabapples flowers remain open for only one to two weeks, flower color progression from bud to bloom is very important as is bloom abundance and the desire to which blooms are borne along the branches. Flower color may vary from white to pink to red and color may change dramatically as buds mature to open blossoms. Red buds may open to pink flowers and pink buds may open into white flowers.
Desirable Cultivars for Maryland
Mark McGuiness of the National Arboretum suggests the following crabapples cultivars for the greater Maryland region:
- Adirondack has a dense, upright, obovate form; dark green disease resistant foliage; large single, white flowers; and bright orange-red small fruit, that persists well into winter. Mature size is 18 feet tall by 16 feet wide.
- Donald Wyman has a rounded form; medium green foliage; single, white flowers; and bright red, 3/8-inch-diameter, abundant, persistent fruit. Mature size is 20 feet tall by 20 feet wide.
- Indian Magic has a rounded upright spreading form; dark green foliage; deep pink, single flowers; and golden orange fruit that persists well into winter until it is eaten by birds. Mature size is 15 feet wide by 15 feet tall.
- Malus floribunda has a horizontal, wider-than-tall form, green foliage, red buds that open over a staggered period to pink and fade to white flowers, and 1/4 inch diameter yellow fruit that ripens early in the fall and is eaten by birds. Mature size is 18 feet tall by 25 feet wide.
- has a dense, shrubby, twice-as-wide-as-high habit, dark green foliage, profuse, single, fragrant, small, white flowers, and small, abundant, bright red, persistent fruit that attracts birds. Mature size is 6 to 8 feet tall by 8 to 14 feet wide.
- Malus x zumi Calocarpa has a rounded spreading, graceful form; green leaves; pink flower buds that open to pure white flower; and glossy red, 3/8 inch diameter persistent fruit that attracts birds. Mature size is 20 feet tall by 24 feet wide.
- Molten Lava has a horizontal to pendulous growth habit; green foliage; pink buds that open to white flowers; and glossy red, 3/8 inch diameter, persistent fruit that attracts birds. Mature size is 15 feet tall by 12 to 15 feet wide.
- Prairifire has an upright form that becomes rounded as it matures; reddish maroon foliage which ages to a dark green’ crimson buds that open to pinkish red, single flowers; and dark red persistent fruit. Mature size is 20 feet tall by 20 feet wide.
- Professor Sprenger has an upright and spreading form; green foliage; pink buds that open to single white flowers; and persistent, 1/2 inch diameter orange-red fruit. Mature size is 20 feet tall by 20 feet wide.