Winter hardy to zone 5, the deciduous hydrangea blooms on large buds formed on previous season’s growth. Any pruning should be done immediately after flowering. It performs well in moist, rich garden soil in partial sun to fairly deep shade. Be sure that tree roots are not competing with the roots since this will slow growth dramatically. Usually hydrangea is free of insect or disease problems. In the florist industry, hydrangeas are forced into bloom by placing them in temperatures below 65°F for 6 weeks to initiate flower buds. Then plants are defoliated and given 6 weeks of complete darkness at temperatures between 33° and 40°. Forcing requires 3 months of 60° nights and 65° to 70° days. A soil pH between 4.5 and 5 and little or no phosphorous gives blue flowers. Pink flowers result from a soil pH of 6.3 to 6.5 and high levels of phosphorous. Pruning is done after flowering. If terminal buds are injured or pruned off, the plant will not bloom. Though florist type hydrangeas may survive planted outdoors in St. Louis they rarely reflower outdoors as the flower buds are frequently killed by winter cold.
Almost everyone is familiar with the enormous, round flower heads of hydrangea, in various shades of white, pink and on acid soils blue. They are borne in late spring to early summer on top of the rounded canopy of rich foliage. The coarse green foliage works well as a foundation plant or accent in a flower garden, or does well in containers for use on shaded patios and decks. Massed together on three to five-foot centers, their foliage makes a strong statement in a shrub border or in other areas of the landscape. If your plant has been received as a florist plant grown in a container, sink the pot in your garden soil during the warm summer months and bring indoors when leaves fall and keep cool but above freezing. Hydrangeas are forced commercially primarily for Easter through Mother’s Day.
Aphids, spider mites, scale, leaf scorch from dry air, drafts or excessive sun; root damage from high salts and dry soil.
Landscape plant or flowering florist’s crop
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