Hydrangea: Great Balls of Pink and Blue

blue hyrdrangea plantIf you have left that shrub with the showy, blue flower clusters to its own devices, but want to know more about the ubiquitous hydrangea, now is a good time to learn more.

Perhaps that shrub growing in the side yard was a potted Easter gift, or maybe it just happened to be there when you moved in. Maybe your hydrangea is blooming pink, and you wonder why it didn’t stay blue. Early July is a great time to take note of hydrangeas in the home landscape, as many are in peak bloom.

Hydrangea flower shapes

Hydrangeas are easy to describe by flower shape:

  • Mophead: large globe-shaped blooms, also known as snowballs or French hydrangeas
  • Lacecap: flat, less showy flower discs, also known as pinwheels or rays
  • Panicles: cone-shaped blooms bearing clusters of florets from a central axis

Hydrangea macrophylla, also known as “big-leafed hydrangea,” includes both the “mopheads” and the “lacecaps”. Hydrangea paniculata is a larger shrub or tree, and the most frost-hardy hydrangea. It sports cone-shaped blooms in mid to late summer. Hydrangea arborescens, known as “smooth hydrangea” or “wild hydrangea,” is easy to grow and has densely-packed, snowball-shaped blooms.

lacecap hydrangea

In USDA Zone 7, hydrangeas are happiest when they receive morning sun and afternoon shade. They also like a moist, but well-drained location.

Hydrangea flower color

Hydrangea colors range from pastel to vibrant. Hydrangea macrophylla is very pH-sensitive. In general, this shrub produces blue flowers in acid soil (6.5 or less) and pink flowers in alkaline soil.

pink hydrangea

But there are some caveats to these rules of thumb. For instance, color can vary from year to year or from flower to flower. And when a plant is moved, the flowers will tend toward red. Note that hydrangeas may be moved at any time.

To make a hydrangea more blue:

  • Add peat and/or sulfur. (125-250 grams of sulfur per square yard to lower pH by 0.5 is recommended.)
  • Add potassium aluminum sulphate. (4 grams per gallon of water; releases slowly)
  • Do not use superphosphates or bone meal when planting.

To make a hydrangea more pink or red:

  • Add dolomitic lime to the base of the plant in spring and fall.
  • Avoid excess alkalinity or leaves will yellow.

Exciting new developments in the world of hydrangeas include red stems, purple flowers and plants that hold their color regardless of soil pH.

Pruning hydrangea

Most hydrangea gardening instructions advise that no pruning is necessary. But always prune to make sure a shrub is well-balanced before planting. Hydrangeas may also need a “rejuvenating” hard pruning about once every three years.

Timing is important. Note if your hydrangea blooms on old or new wood, as improper pruning can destroy next year’s blooms. “Everblooming” varieties actually bloom on both old and new wood.

Hydrangea flowers are long-lasting, which makes them great cut flowers or dried decorations. Old flowers protect the branches’ growing tip, so it is best to leave them on the plant through the winter, if possible. Cut them when new growth is visible.

Buying hydrangeas

Some hydrangeas to look for:

  • H. macrophylla ‘Blue Wave’ - the most popular of the lacecaps, very hardy
  • H. paniculata ‘Pee Gee’ (also known as Hydrangea paniculata 'Grandiflora') - Known as “Tree Hydrangea,” grows from 10 to 25 feet tall
  • H. paniculata ‘Bombshell’ - a dwarf with pure white flowers, blooms profusely
  • H. paniculata ‘Limelight’ - unique green blooms; tolerates full sun; blooms dependably all summer
    limelight hydrangea
  • H. Arborescens ‘Incrediball’ - boasts improved stronger stems and massive flowers
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