Winter Protection for Bigleaf Hydrangeas
How to get next summer’s flower buds through a Canadian winter, and when it is not worth trying.
Winter protection for bigleaf hydrangeas is really protection for their flower buds. Bigleaf hydrangeas form next year’s buds in late summer, so whatever happens to the stems over winter happens to the flowers.
The University of Massachusetts rates bigleaf hydrangea to a mild US zone and says it needs protection one zone colder. In much of Canada that means every winter. Even then it warns that in harsh years the plant may die back or not bloom despite protection.
Bigleaf hydrangea winter protection at a glance: Do not prune in fall. After the leaves drop, set up a cylinder of burlap or chicken wire on stakes around the plant and fill it with leaves or straw. Add a hardware-cloth ring against rabbits. Remove the cover gradually in spring, and keep frost cloth handy for late frosts.
Unsure what to cut? See How to Prune Hydrangeas in Canada for which stems hold next year’s flowers.
What Kills the Buds
The University of Massachusetts names three: low temperatures, fluctuating temperatures, and late frost or freeze events. Its growing guide gives about −12°C (10°F) as the point below which winter can kill all the flower buds, along with early fall and late spring freezes. A cover cannot change the air temperature, but it slows the swings and shields the stems from wind.
How to Protect the Plant
The University of Massachusetts describes wrapping the plant in a cylinder of burlap or chicken wire held up with stakes, then filling it with leaves or straw. Set it up after the leaves drop, before the deep cold.
Protect against rabbits too. The University of Minnesota recommends a large ring of hardware cloth around bigleaf stems in winter, because rabbits browsing the stems remove the buds as surely as frost does.
Do Not Prune in Fall
Every stem tip you cut in fall is a flower you lose. The University of Minnesota says bigleaf plants set next year’s buds in August and September, so prune only right after flowering and before August. Leave the old flower heads on over winter.
Uncovering in Spring
Take the cover off gradually as the weather settles. The University of Massachusetts notes that cold spring temperatures and late freezes can also damage new growth, so keep a frost cloth or old sheet ready for the first warm weeks.
When It Is Not Worth It
In the coldest zones, a bigleaf may survive but rarely flower however well you wrap it. The University of Massachusetts suggests panicle hydrangea as the more reliable bloomer for a difficult spot. The cold-hardy hydrangeas guide matches types to zones.
Frequently Asked Questions
How do I protect a bigleaf hydrangea over winter?
After the leaves drop, put a cylinder of burlap or chicken wire on stakes around the plant and fill it with leaves or straw, as the University of Massachusetts describes. Add a hardware-cloth ring against rabbits.
Should I cut back my hydrangea in fall?
Not a bigleaf. It formed next year's flower buds in August and September, so cutting it back in fall removes them. Prune only right after flowering and before August.
What temperature kills hydrangea buds?
The University of Massachusetts gives about minus 12 degrees C (10 degrees F) as the point below which winter can kill all bigleaf flower buds; early fall and late spring freezes can do it too.
When should I remove winter protection?
Gradually in spring as the weather settles, keeping a frost cloth handy, because late freezes can damage new growth.
Do reblooming hydrangeas need winter protection?
It helps. Rebloomers can flower on new wood after a hard winter, but the University of Massachusetts notes most of their flowers still come from old wood.
Is winter protection guaranteed to work?
No. The University of Massachusetts warns that in harsh years plants may die back or not bloom despite protective measures.
Sources
- University of Massachusetts Amherst Extension — Growing Hydrangeas
- University of Massachusetts Amherst Extension — Why Hydrangea macrophylla Don’t Flower
- University of Minnesota Extension — Pruning hydrangeas for best bloom