When crabapples are planted in a soil of average fertility and provided moderate amounts of organic matter, they need little to no fertilizer. However, if annual growth is less than five to six inches fertilizer may be needed. In general, apply two to three pounds of actual nitrogen per 1,000 square feet of root zone area.
For example, for a fertilizer with an analysis of 20-5-10 (These numbers essentially refer to the percentages of nitrogen, phosphorus, and potassium--NPK--in the bag), to apply two pounds nitrogen per 1,000 square feet, use ten pounds of a 20-5-10 fertilizer spread beneath the trees over an area measuring 31.5 feet by 31.5 feet or its equivalent (not applicable for small trees!).
Pruning
Crabapples require little pruning. Watersprouts (rapidly growing shoots from branches), suckers (rapidly growing shoots from roots or base of tree), dead, diseased, damaged, and crossing branches should be removed. Watersprouts will not re-grow as vigorously if removed in mid-summer. Occasionally pruning is necessary to open up the center of the plant to sunlight and air movement or to remove a wayward branch.
When pruning is done it should be completed before early June. By mid-June to early July, flower buds for the next season are beginning to form in most crabapples. Pruning after July will reduce floral display and fruiting for the following year.
Irrigation
If trees are well established after the first year, little additional watering is needed unless drought conditions prevail. In a drought situation it is necessary to water thoroughly and deeply as needed. Depending on the soil type and drought severity, a couple of inches of water should be applied at each watering interval.
