Growth: Hydrangeas are relatively non-finicky plants. They will grow in a multitude of soil conditions including clay, stony or sandy that are either alkaline or acidic. Naturally, hydrangeas are found in either full sun or in dappled shade provided by deciduous trees. Deep shade, like that provided by dense evergreens, tends to lead to unthrifty plants. It should be noted that hydrangeas require ample moisture and will perform poorly if it is not provided in either condition. Scorch is not an uncommon problem for plants in a sunny, dry position.
Flowering: A summer-flowering plant, the flower heads usually consist of a mix of sterile and non-sterile flowers. Most flowers change color when they age. The sterile flowers don’t fade and go to seed, which is the reason for their long blossoming time. Flower color for macrophylla and serrata hydrangea types tend to be influenced by soil acidity.
Feeding: It is beneficial for hydrangeas to receive a spring feeding with a balanced fertilizer high in nitrogen and a top dressing of compost. When adjusting pH to influence bloom color towards blue, use a fertilizer high in nitrogen and potash, and low in phosphates. Avoid superphosphates as they tend towards alkalinity. Gar- den sulfur is one of the best additives for increasing soil acidity.
When adjusting pH to influence bloom color towards pink/red, use a fertilizer with high phosphorus. Dolomite lime is one of the best additives for decreasing soil acidity. For the above pH adjustments, apply 1/3 of the annual amount 3x a year so as not to burn the roots. Be persistent; it may take up to 3 years for a hydrangea to settle into its permanent color.
Pruning: As a group, hydrangeas are unique in that the best time to prune them is during winter. Each group has slightly different requirements, but in general remove dead and diseased branches, thin weak stems and reduce the height as desired. Selective pruning has the added benefit of increasing the quality and size of the flowers.
*In the fall, after the plants have gone dormant, certain varieties require 12 inches of mulch
for winter protection directly over the center of the plant. Most of these varieties are found in the macrophylla and serrata families. Ask your nursery professional for further
Disease and pests: Hydrangeas are relatively pest-free. Slugs and snails may occasionally bother the macrophylla types; control with slug bait. Mildew could be a problem in wet, humid summers; apply a fungicide to control it.