Hort Minute from October '13 Meeting

From Gail Anderson, IGC Horticulturist
Have a question or want to suggest a topic for Hort Minute? Please e-mail Gail at riverfront37@verizon.net.
Question: “How do you prune hydrangeas?”
Submitted by Carol Williams (Thank you!)

General Rules of Thumb
•    Many hydrangeas do not need pruning. Simply cut off dead tips or branches in the spring.
•    If you must prune heavily to control size, the plant is in the wrong place.
•    Do not prune any hydrangeas between September and January
•    Do not “shear” hydrangeas. That is, do not cut them uniformly tight like a hedge. Cut individual stems.
•    When pruning, use hand pruners or a small hand saw, not mechanical tools.
•    Do not remove more than 1/3 of the stems in one season.
•    Remove dead flowers any time you wish.

Two Questions
Ask only two questions:
WHEN to prune?
HOW to prune?

WHEN TO PRUNE is determined by the species (type) of hydrangea
Depending on the species, hydrangeas form flower buds in one of two ways:
On NEW growth of the current season
On OLD growth of the previous season
When to prune will be determined by the time of flower bud formation. You want to avoid cutting off buds of future flowers.

Too complicated? See the WHEN and HOW of the four most common hydrangeas below.

HOW TO PRUNE is determined by the shrub’s overall shape (habit)
    Canes: If your hydrangea has canes (stems) that grow straight from the ground without branches (like a porcupine), cut the tallest or floppiest canes to the ground. Do not cut canes halfway.
    Branched: If your hydrangea has stems with branches, prune back to a crotch.
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Smooth Leaf Hydrangea (Hydrangea arborescens)

WHEN? Prune late winter/early spring
(Blooms on new growth)

HOW? Cut tallest or floppiest canes to the ground
Note: Can be completely cut to the ground—optional, done every few years in winter or very early spring.
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Panicle Hydrangea (Hydrangea paniculata)

WHEN? Prune late winter/early spring
(Blooms on new growth)

HOW? Cut branched stems or twigs to a crotch
Cane forming varieties: Cut tallest or floppiest canes to the ground

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Oakleaf Hydrangea (Hydrangea quercifolia)

WHEN? Prune immediately after blooming (early-mid summer)
(Blooms on old growth)

HOW? Cut branched stems to a crotch or to the ground
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Big Leaf Hydrangea (Hydrangea macrophylla)

WHEN?
Old fashioned: Prune immediately after blooming (mid-summer)
Blooms once a season on old growth

Reblooming (new): Prune immediately after first flush of bloom (mid-summer)
Blooms on old and new growth
Note: Deadheading spent flowers will encourage reblooming

HOW? Cut tallest canes to the ground