Botanical name: Hydrangea
Plant type: Shrub
Soil type: Any
With immense flower heads, hydrangeas flaunt an old-fashioned charm that is hard to resist. Colors also beguile with clear blues, vibrant pinks, frosty whites, lavender, and rose—sometimes all blooming on the same plant!
The colors of some hydrageas—especially mophead and lacecap—can change color based on the soil pH which affects relative availability of aluminum ions. Acidic soils with a pH of less than 5.5 produce blue flowers; soils with a pH greater than 5.5 product pink flowers. White flowers are not affected by pH.
Unrivaled in the shrub world, these elegant ladies are easy to cultivate, tolerate almost any soil, and produce flowers in mid-summer through fall (when little else may be in bloom). Hydrangeas are excellent for a range of garden sites from group plantings to shrub borders to containers.
- Most hydrangeas thrive in rich, porous, somewhat moist soils. Add compost to enrich poor soil.
- They prefer full sun in the morning, with some afternoon shade; however, many will grow and bloom in partial shade. This is especially true for the bigleaf hydrangeas (see Recommended Varieties below).
- Plant in spring or fall.
- Dig a hole as deep as the root ball and 2 to 3 times as wide.
- Set the plant in the hole and fill it half full with soil. Water. After water is drained, fill the rest of the hole with soil.
- Water thoroughly.
- Space multiple hydrangeas about 3 to 10 feet apart.
- For the first year or two after planting and during any drought, be sure hydrangeas get plenty of water. Leaves will wilt if the soil is too dry.
- If your soil is rich, you may not need to fertilize hydrangeas. If your soil is light or sandy, it's best to feed the plants once a year n late winter or spring. Too much fertilizer encourages leafy growth at the expense of blooms.
- In the fall, cover plants to a depth of at least 18 inches with bark mulch, leaves, pine needles, or straw. If at all possible, cover the entire plant, tip included, by making cages out of snow fencing or chicken wire, and loosely filling the cages with leaves. (Do not use maple leaves.)
How to Prune a Hydrangea
Many of our readers' questions are about pruning a hydrangea. And no wonder it's confusing! It depends on the variety of hydrangea.
Common Hydrangea Shrubs
- The most common garden hydrangea shrub is the Bigleaf variety, H. macrophylla). One type of Bigleaf is the "Mophead" with the big snowball-size blooms. The other type of Bigleaf is the "Lacecap" with the pretty flowers almost hanging down from a flat center of tiny blooms.
- The Bigleaf variety or,H. macrophylla, as well as H. paniculata and H. quercifolia are pruned AFTER the flowers fade.
- Flower buds actually form in the late summer and flower afterwards the following season, so avoid pruning after August 1.
- Only cut away dead wood in the fall or very early spring.
- To prune, cut one or two of the oldest stems down to the base to encourage branching and fullness.
- If the plant is old or neglected or damaged, prune all the stems down to at the base. You'll lose the flowers for the upcoming season, but also renovate the plant for future years.
- It's best not to deadhead (remove faded blooms) on the big mopheads; leave them over the winter and cut them back in early spring (to the first healthy pair of buds). It's fine to deadhead the lacecaps; cut down to the second pair of leaves below the flower head.
- Oakleaf, panicle, and smooth hydrangeas are treated differently. They blossom on the current seasons' wood. They should be pruned in the later winter when the plant is dormant BEFORE bloom. This means if the buds are killed during the winter, they will produce new buds in the spring which will produce blooms.
- In general, prune only dead branches, and do not prune to "shape" the bush.
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Try drying hydrangea flowers to create a wreath or other decorations around the house:
- Harvest the heads when the flowers have matured and developed a papery consistency.
- Remove leaves from stems, and hang upside down in a warm, dry, dark, airy room.
- When completely dry (usually a couple of weeks), store in a dry location out of direct sunlight.
- To enhance flower color, spritz dry flowers with diluted Rit dye.
There are two main groups of hydrangeas.
Group 1: Plants that bloom on new growth (this year's stems)
These hydrangeas, which form their buds in early summer on new growth, will flower reliability each year, requiring no special care.
- Panicle hydrangeas ( H. paniculata) are hardy to Zone 3 and boast fat, cone-shaped flower heads. They are a good choice for a beginner. The most common cultivar is 'Grandiflora', or P.G. (PeeGee) after its initials, a big old-fashioned floppy shrub that is 10 to 15 feet tall.
- Smooth hydrangeas (H. arborescens) or "snowballs" are excellent for cold climates, flowering reliability in Zone 3. The flowers look like oversized white-flowered pop-poms. Look for cultivars 'Grandiflora' and 'Annabelle' which produce large blooms in late summer.
Group 2: Plants that bloom on old growth (last year's stems)
If you live in Zone 8 or warmer, choose plants from this group.
- Oakleaf hydrangeas (H. quercifolia) exhibit incredible bud hardiness and thrive in Zone 5. This graceful plant is noted for its spectacular fall colors that range from red to purplish burgundy. The flower heads turn a rich brown that lasts all winter. Try 'Snow Queen', 'Snow Flake', and 'Alice.'
- Bigleaf hydrangeas (H. macrophylla) are the most common species and come in two flower shapes: Mopheads (or Hortensias) which are hardy to Zone 6 and bear large, ball-shaped flowers and Lacecaps which are suitable for Zones 5 to 9 and form airy, elegant, flat-topped clusters of flowers. We love 'All Summer Beauty' (Hortensia) which has profuse, dark blue flowers, pinker on soil near neutral. 'Nikko Blue' (Hortensia) is vigorous, with large, rounded blue flowers. 'Blue Wave' (Lacecap) produces rich blue to mauve or lilac-blue to pink flowers.
- Climbing hydrangeas are just magnificent, lighting up the trunk of a tall tree. This vine blooms from late June to early July, exhibiting flat, lace, creamy-white flowers against glossy leaves.
Wit & Wisdom
Changing the Color of a Hydrangea
It is possible to change the flowers' colors but not instantly. Color correction takes weeks, even months. It is easier to change blue flowers to pink than pink to blue. Wait until the plant is at least 2 years old to give it time to recover from the shock of its original planting.
- Start with the Hydrangea macrophylla variety. Have your soil pH tested.
- To get blue flowers, you need to lower the pH, which you can do by adding sulfur or peat moss to the soil. To get pink to light red flowers, add ground limestone only around the plant; a pH above 7.5 will result in poor growth.
- Note that hard water can affect the flower colour, turning blue flowers more pinkish so use rainwater to water your hydrangeas.
- In the fall, hydrangea flowers will naturally fade, often to a combination of pink and green. This is simply the aging process which can not be reversed. Next year, the flowers will return to their original color.