Botanical name: Hydrangea
Plant type: Shrub
Soil type: Any
With immense billowy blossoms, 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 H. macrophylla flowers are affected by the relative availability of aluminum ions in the soil. 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.
- When growing H. macrophylla varieties in Zones 4 and 5, don't prune unless absolutely necessary, and then do so immediately AFTER blooming. Otherwise, remove only dead stems in the spring.
If you need to prune an older hydrangea, it depends on which variety you have.
- The common Bigleaf hydrangea should be pruned AFTER flowers fade (late spring/early summer). If you prune before bloom, you may not have blossoms the following spring.
- Oakleaf, panicle, and smooth hydrangeas blossom on the current seasons' wood so they should be pruned BEFORE bloom when plant is dormant, i.e. late winter or early spring.
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.)
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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
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 fro 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.