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Hydrangea 101

We know it can be a daunting process trying to decide which hydrangea is best suited for your landscape. We are going to break it all down and demystify these beautiful shrubs.

Let's start with the six main types commonly grown in North American gardens:

Big-leaf (Hydrangea macrophylla) Hardy to zone 5

also known as florist's hydrangea, hortensia,mophead or lacecap

bigleafhydrangea

Panicle (Hydrangea paniculata) Hardy to zone 3

also known as peegee hydrangea

paniclehydrangea

Smooth (Hydrangea arborescens) Hardy to zone 3

also known as Annabelle hydrangea

smoothhydrangea

Climbing (Hydrangea petiolaris) Hardy to zone 4

climbinghydrangea

Mountain (Hydrangea serrata) Hardy to zone 5

mountainhydrangea

Oakleaf (Hydrangea quercifolia) Hardy to zone 5

oakleafhydrangea

All hydrangea have similar cultural needs, requiring:

  • Moist but well-drained soil (hydrangea will not tolerate wet feet - ever!)
  • Some sun each day. Most people think of hydrangea as shade plants, but they look and flower best with at least 4 hours of sun, ideally in the morning. Panicle hydrangeas are the most sun tolerant, and can take full sun in the northern climates.
  • Plenty of water, especially as they are getting established. Hydrangeas have shallow roots, so they dry out quickly. A 2-3" thick layer of bark mulch is a useful addition to any hydrangea planting.

Flowering

  • Panicle and smooth flower on new wood. Flower buds on these hydrangeas form after the plant leafs out in spring, and open a few months later in summer. These plants flower reliably no matter how cold the winter was.
  • Big leaf, mountain, oakleaf and climbing flower on old wood. Flower buds on these hydrangeas begin to form in late summer and must remain undisturbed all through the fall, winter, spring, in order to flower the following summer. Pruning these types of hydrangea will remove potential buds. They can also be browsed by deer, which will eat potential buds. These types can also be damaged by weather. The cold weather isn't the problem, it is in spring, when several days of warm temps are followed by a sudden freeze, that flower buds are most likely to be damaged.
  • Reblooming hydrangeas are types of big leaf and mountain that have the ability to flower on both new and old wood. Even if the buds are damaged in winter weather, the plant can still flower on new wood it produces that season.

Pruning

  • Avoid pruning rebloomers and those that flower on old wood. Instead, site these appropriately so they do not need to be pruned and choose varieties that don't get to big for their space.
  • New-wood hydrangeas can be pruned each early spring, just as new growth emerges.
  • Hydrangeas do not strictly require regular pruning. They will grow and flower well with nothing more than the removal of spent flowers and any dead wood each early spring.

Color

All hydrangeas undergo some color change as the flowers age, but only big-leaf and mountain hydrangeas can change their color in a predictable, controlled way. The pH isn't the only thing responsible for the change. It is the presence of aluminum in the soil that causes a change in color.

Generally speaking, the more intense the color, the less likely it can be altered. It is much easier to change pink to blue than from blue to pink. Both endeavors involve making chemical applications at specific times and in specific amounts. Garden lime and soil acidifier can be added to your soil to raise or lower pH. Both are available at the garden center.