The crab apple tree (Malus), like the apple tree, belongs to the rose plant family (rosaceae) but differs from the apple on account of fruit size. Any fruit 2 inches or less in diameter is a crab apple and any fruit larger than 2 inches is an apple, according to the Tree Help website. Crab apple trees are rounded, upright, pyramidal, spreading or weeping, and grow to a mature height of 15 to 25 feet. The trees bloom with single, double or semi-double flowers during spring in shades of whites, pinks and reds making them a popular ornamental trees. Crab apple trees are easy to grow and need little pruning to keep in shape.
Purple Prince Crab Apple
The purple prince crab apple tree is rounded in shape and grows to a height of about 20 feet with an equal spread, according to the Lark Nurseries website. The tree blooms with rose-red flowers and has bronze-green foliage that turns purple during fall. Purple prince is a fast-growing variety that is resistant to breakage. The fruit of the purple prince is dark maroon in colour and 1/8 to 1/2 inch in diameter. Purple prince has excellent resistance to apple rust and fire blight and a moderate resistance to mildew.
Royal Fountain Crab Apple
Royal fountain crab apple is a weeping crab apple variety and grows to a mature height of about 15 feet, according to the Lark Nurseries website. The tree has a 15-feet spread and has bronze-green foliage that changes purple in the fall. The flowers of the royal fountain are rose-red and the 3/8- to 1/2-inch fruit is deep red. The branches of the royal fountain start to display their weeping growth habit while the tree is still quite young. The tree is resistant to apple rust and mildew and moderately resistant to fire blight.
Adirondack Crab Apple
According to the Lark Nurseries website, adirondack crab apple is among the most favoured varieties of crab apple used as an ornamental given its upright, slightly inverted cone shape and its striking display of flowers. The tree is compact and dense, and blooms heavily with white flowers during the spring. The tree grows to a mature height of about 18 feet with a 10-feet spread. The foliage is medium green and the 1/2-inch fruit is bright red. Adirondack is highly resistant to scab, cedar-apple rust, fire blight and mildew. The adirondack crab apple variety was introduced by Don Egolf of the U.S. National Arboretum.
Centurion Crab Apple
Centurion crab apple tree is narrow in growth and grows to about 20 feet with a 15-feet spread, as cited by the Lark Nurseries website. The tree blooms with rose-red flowers and has glossy, light green foliage. The tree produces a heavy amount of red, 3/8-inch fruit. The younger trees are upright but assume a more upright spreading form as they mature. Centurion crab apple has superior resistance to cedar-apple rust and mildew and a moderate resistance to scab and fire blight.