Hydrangea blooms head by head: dozens of small flowers crowding into one ball, weighing the branch tips down, a single clump able to hang a dozen balls. The strangest thing is the color—acidic soil turns it blue, alkaline soil pink.

Flowers That Hold Together in Balls

Hydrangea blooms in balls: each head is gathered from many small flowers, crowded tight, bloom against bloom, almost too round. Its leaves are large and thick with toothed edges, making the flower heads look all the neater.

In fact, the showiest rings around the ball are mostly sterile flowers—the petal-like parts are enlarged sepals, and the true flowers hide within. The head is round because the whole clump’s strength has been spent on the outer ring.

— Botany Notes, self-inscription —

A courtyard of gathered snow, changing with the seasons;

it asks no right or wrong of the human world.

Blue or Pink—the Soil Decides

Hydrangea’s most famous trait is that its color follows the soil: on acidic ground it blooms mostly blue, on alkaline ground mostly pink, with purples and transitions in between.

The reason lies with aluminum in the soil: under acidic conditions aluminum is taken up and binds with anthocyanins to show blue; under alkaline conditions it is not absorbed and the color turns toward red-pink. Ornamental gardens therefore control color by adjusting the soil—the same cultivar can open in two colors.

One of the Most Generous Bloomers of the Courtyard

It likes half shade and moisture and fears strong sun—best planted on the east side of a courtyard or in the thin shade of a large tree. The soil should be loose and water-holding; in summer it must not go dry, or the flower heads collapse.

The heads are heavy and the branchlets thin, so wind and rain topple it easily—leave room around the plant or add supports. In the month of bloom, a single clump can open a dozen heads; it is one of the most generous flowers a garden can have.

• How to know it: Deciduous shrub; leaves large, opposite, toothed; corymbose inflorescences forming large balls, mostly sterile flowers around the outside, blooming May–July.
• Season: Blooms May–July; heads last about a month; leaves yellow in autumn; winter sheds leaves but keeps branches.
• Caution: Likes half shade and moisture; avoid strong sun and drought; pruning must follow whether the cultivar blooms on old or new wood.

Pruning Depends on the Cultivar

Hydrangea must be pruned by cultivar: bigleaf hydrangeas mostly bloom on old wood—prune lightly after flowering, and do not cut the old wood away in winter and spring, or next year brings leaves without flowers; some new-wood cultivars, however, accept hard pruning in early spring.

Knowing which class your hydrangea belongs to is the first step to growing it well. Pruning is a question: first learn where it makes flower buds, then decide when to take the scissors.

◆ ◆ ◆

Keywords: hydrangea · color control · courtyard · half shade