Hydrangea arborescens 'Annabelle' will tolerate a wide range of conditions and produce large, white flower heads that measure 10 inches across. The plant is not particularly fussy. It is extremely hardy, withstanding temperatures as low as -30 degrees F, and will do well as far south as Georgia. Due to its large flower size it does need protection for high winds and will benefit from staking.
Soil and Fertilzer
H. arborescens 'Annabelle' prefers rich, moist, well-drained soil that is not soggy. It benefits from the addition of organic matter such as compost, leaf mold or manure. Soil acidity is not important. If the soil is a heavy clay, work in some sand and peat moss when planting. Fertilize H. arborescens in late spring with a slow-release, balanced fertilizer for flowering plants. Do not fertilize it after mid-August, as this can promote winter damage.
Annabelle will tolerate more sun than most hydrangeas, especially in the northern part of its range. In warmer regions, choose a spot that receives morning sun and dappled shade in the afternoon. It will not do well in deep shade anywhere in its range.
Although Annabelle prefers moist soil, over-watering will result in root rot. Watering is important during the first couple of years and during droughts. Check below the surface before watering.
Best Time to Plant
Annabelle is best planted in early summer or late fall. When possible, purchase container grown plants in bloom. Wild species of H. arborescens will give disappointing results. Set the plant at the same depth as it was planted in the container. If planted too deeply it will not perform well. Mulching the plant until it is established will help maintain needed moisture and an even soil temperature.
Annabelle blooms on new wood so pruning down to the ground will not hurt it. The stems will support the flower heads better if they are not pruned all the way back, but are allowed to thicken with age. Remove dead, damaged or weak stems in later fall or early winter.
Pests and Diseases
A number of fungus diseases attack hydrangeas. Most occur during periods of cool, wet weather, and include powdery mildew, black spot and grey mold (botrytis blight). During warm, wet weather anthracnose can be a problem. All these conditions can be controlled by applying a fungicide and practicing good sanitation. Remove all plant debris and sanitize gardening tools.
Mushroom root rot is a more serious problem. An otherwise healthy plant will suddenly develop one or more wilting shoots. The shoots will not recover when watered and the wilting will spread to the rest of the plant. There is no cure. Pull and destroy infected plants.
Pests that attack hydrangeas include aphids, scales, whiteflies, thrips, spider mites and weevils. Insecticidal soap can be used to control most pests. Your garden center can give you advice if something stronger is needed.