- Summer has reached its peak, and so has that most emblematic of Hamptons garden flowers - the hydrangea. Those big blue pompoms seem to be everywhere right now. This week From the Garden takes a look at the hydrangea clan.
A classic blue mophead.
There are more than 80 species of hydrangeas, and countless varieties of the most popular cultivated kinds, with new ones arriving in local and mail-order nurseries every year. Here's a rundown on some of the best.
The iconic Hamptons hydrangea is a big-leaved type belonging to the species macrophylla. The most widely grown ones are the mopheads, or hortensias, which have big round pompom flowers that are mostly blue. The color can change according to the pH of the soil. This species is native to the coast of Japan, which probably explains why it takes to our sandy soil and salty air. The plants can grow to six feet high and equally wide. Nikko Blue is one classic variety. Endless Summer is a newer one that blooms through most of the summer and well into fall. There are also varieties with red, mauve, pink or white flowers. Blushing Bride starts out white and turns to pink as the flowers age. For a small space, try the dwarf red-pink variety Pia.
The elegant lacecap varieties of this species have flat, airy flowerheads that are made up of a central cluster of tiny round fertile flowers (that can produce seeds) surrounded by a ring of larger sterile (non-seed-producing) flowers.
Bluebird and Mariesii are two blue-flowered varieties. Lanarth White has white blossoms and Veitchii has two-toned blue-and-white flowerheads.
If you want to prune macrophylla hydrangeas, do the pruning right after the flowers stop blooming.
What Color Are They, Really?
The color of blue and pink hydrangeas is influenced by the pH of the soil they grow in. The flowers are blue in acid soil and pink in alkaline soil. To make your hydrangeas blue, or bluer, add sulfur (the organic kind is derived from elemental sulfur) or aluminum sulfate (both are available at many garden centers) to the soil. Fertilizing with a fertilizer formulated for acid-loving plants (such as HollyTone) also helps keep the flowers blue. To make your hydrangea flowers more pink, add lime to the soil.
The native smooth-leaved hydrangea (Hydrangea arborescens) grows as a clump of tall stems and bears large white flower clusters in early to midsummer. Annabelle is the best-known variety. This species blooms on new wood (shoots formed during the current growing season), and can be cut back in early spring. The plants are generally hardier than the macrophyllas.
Peegee (Panicle) Hydrangeas
Another popular species, Hydrangea paniculata, grows taller and blooms later in summer than mopheads or Annabelles. The plants are tougher and less moisture-sensitive, too, and their color is not affected by soil pH. The peegee hydrangea (Hydrabgea paniculata 'Grandiflora') has snowball-shaped flowerheads. Other fine varieties are Tardiva (with large, conical white flowerheads), Pink Diamond (which starts out greenish, then turns white, then rosy and finally greenish pink). A new one, Quick Fire, blooms earlier than the others, with big cone-shaped flower clusters that open white, then gradually turn pink, then deep rosy red in fall.
Other Noteworthy Hydrangeas
Another classic blue mophead.
Other hydrangeas for your garden include the oakleaf, whose lobed leaves somewhat resemble their namesake. It bears pyramidal white flowerheads and sports rich red autumn foliage. The lovely climbing hydrangea has white lacecap flowers in late spring, and glossy, deep green leaves. It's delightful climbing a tree trunk (it won't hurt the tree).
Why They Don't Bloom
If your hydrangeas fail to bloom, there are several possible reasons.
• The most common cause is pruning at the wrong time of year. Macrophylla and paniculata hydrangeas set their buds for the following year's bloom after the current season's bloom is over. Pruning in spring can remove the buds.
• A late spring frost can kill the flower buds after they've begun to grow.
• Deer love hydrangeas and may snack on tender shoots, along with the flower buds.
• Too much fertilizer - especially one high in nitrogen—can hinder flowering, too.
Smooth-leaved hydrangeas make a flowery, billowy hedge.
• Hydrangeas aren't difficult to grow. Give them regular moisture and a balanced fertilizer. A blended organic product will release its nutrients gradually, which is beneficial to the plant.
• There's really no need to prune them unless the plants outgrow their space, except to remove dead, dry stems.
• Hydrangea flowers are long lasting, but eventually you will need to remove the old, dry flowerheads. If you wait until spring to do it, cut back the old flower stems only to the uppermost pair of buds on the stem. Don't cut off any green shoots - that's where this year's flowers will grow.
Most of all, be sure to cut plenty of the flowers to fill vases all around your house and deck.
Anne is a writer, editor and professional gardener, and the author of 17 garden, home and nature books. She lives in Hampton Bays.