Extension Educator, Horticulture
It's spring and the flowering trees are in their glory. Few ornamental trees offer the variety of tree shapes, sizes, flower colors and ornamental fruit as flowering crabapples. There are over 500 cultivated varieties of crabapples.
Flowering dates range from early April through mid-May. Flower colors may be white, pink to red. Tree height varies from 6 to 50 feet with most in the 15 to 25 feet range. Their variety of growth habit from weeping, spreading, columnar, vase-shaped to pyramidal means many opportunities for their landscape use.
We are tempted to buy crabapples just on their flower color alone. That's like buying a car just because you like the color of the interior. First item should be disease resistance. Before purchasing a crabapple spend some time researching cultivars or go to a garden center you trust. Avoid older varieties such as 'Hopa', 'Almey', 'Royalty' and 'Eleyi' because of their susceptibility to diseases. Plant trees resistant or at least moderately resistant to fire blight, apple scab, cedar apple rust and powdery mildew.
Apple scab is a common crabapple disease. Severely blemished leaves drop in late summer. Most crabapples survive apple scab infection, but their ornamental value is questionable. Summer is short enough without seeing bare trees in August.
Fungicide sprays can be used throughout the spring to reduce infection from diseases, but the sprays must be applied regularly every year before infection occurs. Once trees are infected, fungicides show little effect.
For crabapples prone to apple scab, fungicides containing chlorothalonil, copper sulfate or potassium bicarbonate can be sprayed when leaves just begin to emerge from buds and continue at labeled intervals to two weeks past petal fall. We are past leaf emergent but sprays could be applied to protect additional leaves as they emerge. The best control is planting resistant varieties.
Depending on where you live in the state, Japanese beetles may also plague crabapples. Not all cultivars have been tested for susceptibility to Japanese beetles and information can conflict depending on the source. A study out of Purdue listed 'Bob White', 'Jack', 'Ormiston Roy', 'Molten Lava', 'Prairifire', Japanese Flowering, 'Sargent' and 'Harvest Gold' as just some of the cultivars that showed some resistance to apple scab and Japanese beetles.
Along with disease resistance, look for varieties with small fruit or fruit that persists into winter until the frozen apples shrivel or are eaten by birds. Larger fruited varieties are attractive, but the fruit can be messy around patios and sidewalks.
With so many wonderful cultivars it's hard to highlight just a few. '
A nice small crabapple is 'Sargent' with its single white flowers and 1/3-1/2 inch dark red fruit. At maturity 'Sargent' is 6 to 8 feet tall (perhaps 10) and one and one half to twice that in width. In the landscape it is a nice tree for a focal point.
For something a bit different there are some nice cultivars with persistant yellow fruit. 'Harvest Gold' and 'Golden Raindrops"'('Schmidtcutleaf') both show good disease and Japanese beetle resistance.
For more information: Manual of Woody Landscape Plants by Michael Dirr.