The hydrangea (hydrangea macrophylla) is a broad-leafed shrub grown in many parts of the United States. The outstanding feature of the hydrangea shrub is the large flower, called an inflorescence, that is made up of hundreds of small flowers. The inflorescence may be blue, pink, white or green, depending on hydrangea variety. A unique feature of the hydrangea is that the flower color often depends on the acidity or alkalinity of the soil. Certain growing procedures are required to keep a hydrangea shrub healthy and encourage it to bloom.
Select the right variety of hydrangea that grows in your USDA horticultural zone. When purchasing a hydrangea plant, look on the tag or in the plant description to find out the suitable planting zone. A hydrangea that is planted in an area where the new growth or tender flower buds freeze every year may never bloom because the blooms are produced on new wood.
Plant the hydrangea shrub in deep, moist garden soil enriched with compost. The root base of the plant should be covered with a 1- to 2-inch layer of mulch. Mulch prevents weeds from competing with the plant and prevents wide fluctuations in soil moisture levels. Uneven moisture levels can have an adverse affect on bloom production. The soil around a hydrangea shrub should be kept moist, but not wet, during the entire growing season.
Locate the hydrangea shrub in a place in the garden where it is protected from the hottest afternoon sun. Hydrangeas are prone to wilting in the heat of the day if there is too much sun exposure. Excess heat can also cause blooms to be stunted or wilt. On the other hand, too much shade can limit bloom production. Exposure to four or five hours of morning sun during the growing season is best in most parts of the United States. In cloudy or cooler locations hydrangeas can have more sun exposure without adverse affects.
Fertilize the hydrangea shrub with a fertilizer specific to the plant. Read the directions carefully on the hydrangea fertilizer container label and use as directed. Never over-fertilize a hydrangea shrub or the plant will produce lots of green, tender and leafy growth at the expense of bloom production. Also, tender new growth is susceptible to insect damage.
Prune the hydrangea shrub right after the bloom period. This allows new wood to grow over the season for new blooms the following spring. If you wait until fall or winter to prune the hydrangea shrub, you will prune off the buds that create next year's blooms. For "Ever-Blooming" hydrangeas that bloom several times a year, prune as soon after each bloom period as possible.