Hydrangea serrata 'Blue Billow'

Latin Name Pronunciation: hye-dran'jee-uh 

Growing H. serrata

Light/Watering: Most varieties thrive in full sun in the North, but in the South require afternoon shade. Moist soils that do not dry out are best; do not plant in hot, dry, exposed sites. Mulch to conserve moisture and buffer soil temperatures.

Fertilizer/Soil and pH: In some varieties, flower color is determined by the pH of the soil; at low pH (acid soils) flowers will be blue and at higher pH, flowers will be pink. Generally, a pH below 5.0 results in deep, vivid blues and as the pH rises the flowers range from blue to lavender to mauve to a vivid deep pink at pH 7.0 (neutral). The pH determines the availability of aluminum in the soil; this element is more readily available in acid soils, and this availability results in the blue flower color. Since phosphorus ties up aluminum in soils, using a fertilizer low in this nutrient will aid in attaining blue flowers. If pink flowers are desired and your soil is acid, simply add lime to raise the pH and use a balanced fertilizer. Aluminum sulfate will lower pH if blue flowers are desired.

How to test your soil?

We recommend that you visit your local Cooperative Extension Service to find out about soil testing in your area. Follow this link for a directory of institutions involved in the Cooperative Extension program.

Pests/Diseases: None serious. Occasionally powdery mildew will infect the foliage, especially in humid areas with poor air circulation. Treat with an appropriate fungicide if the problem is serious, and be sure to rake up and destroy all fallen foliage in the autumn.

Pruning: Little pruning is needed, but if shrubs grow too large, cut back stems by about one-third by the end of August. In spring, only prune out dead wood. Most Hydrangea serrata varieties bloom on old wood. H. s. Tuff Stuff™ is a variety that blooms on both old and new wood. If no fall pruning was done, stems can be cut back by one-third in spring if necessary—but this will sacrifice the bloom on the old wood and shrubs will not flower until late summer.

Transplanting: Young plants may be transplanted when dormant in early spring; larger tree-form varieties are difficult to move once established, but it can be done. Prune top growth after transplanting to reduce water loss.

End of Season Care: Rake up and destroy any fallen foliage that was infected by powdery mildew or other fungi.

Calendar of Care

Early Spring: Prune out any dead wood from all varieties. Check soil pH and adjust up or down if needed for desired flower color. Feed plants with a fertilizer high in phosphorus (such as 15-30-15) to encourage blooms. Complete any transplanting before leaves unfurl.

Mid-Spring: Mulch plants after soil has warmed to conserve moisture and buffer soil temperatures. Watch for powdery mildew and treat as needed.

Summer: As soon as blooms fade, remove old flowering stems. If needed, prune as indicated above by the end of August.

Fall: Remove and destroy any fallen foliage that was infected by powdery mildew. If not pruned in spring, plants can be shortened, or pruned back to the ground.

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