Find Your Zone, Check Your Species
To understand which hydrangeas need protection, determine the lowest temperature likely in your garden by consulting the USDA Hardiness Zone Map . The map bases its estimates on years of historical data.
Protection through the winter varies by species. The common hydrangea species are
- Hydrangea anomala subsp. petiolaris (climbing hydrangea, a vine)
- Hydrangea arborescens (smooth or native hydrangea eg., 'Annabelle')
- Hydrangea aspera
- Hydrangea macrophylla (bigleaf hydrangea the most common species eg., 'Nikko Blue')
- Hydrangea paniculata (panicle or PG hydrangea eg., 'Tardiva')
- Hydrangea quercifolia (oakleaf hydrangea eg., 'Snow Queen')
- Hydrangea serrata (mountain hydrangea eg., 'Blue Billow')
Take Action If ...
...the lowest temperature in your garden is
- Always above 0 degrees F No protection of any species needed through the winter. Once established, all commonly grown hydrangea species are cold hardy in this temperature range.
- Always above -10 degrees F Protect Hydrangea aspera and certain selections of Hydrangea macrophylla.
- Always above -20 degrees F Protect Hydrangea macrophylla..Hydrangea serrata and Hydrangea quercifolia (depending on the cultivar) may need protection.
- Always above -30 degrees F Protect all hydrangeas except for Hydrangea arborescens & Hydrangea paniculata.
- Always above - 40 degrees F Protect all hydrangea species.
If your hydrangeas are young or newly planted , you may need to take extra precaution.
How to Protect Your Hydrangeas
Hydrangea macrophylla & hydrangea serrata species most commonly require winter protection.
Encircle the shrub with a wire cage.
Carefully wrap the stems using burlap or spunbonded polypropylene ("Reemay" is one of many brands)
and/or fill the cage with a lightweight mulch (pine straw, hay, straw, deciduous leaves).
This process helps to protect the flower buds along the lower portion of the old stems, which will flower if not killed by cold even if the terminal bud is lost. Leave protection in place until after risk of frost has passed. Be careful when you remove the protective construct so that you don't pop off any buds along the stems.
Protecting Emergent Buds at Winters End
Any garden is at risk from a late cold front moving in just when we, and the hydrangeas, thought that spring was finally here. You can either gamble that your losses won't be great, or you can cover the shrubs for the spell of freezing weather.
If you choose to cover your plants, cover them completely to the ground. The ground helps maintain a warmer temperature within the covering.
Use whatever you can get your hands on garbage cans, large plastic pots, sheets, blankets, fur coats, frost blanket material and secure the cover to the ground with whatever is at hand bricks, pieces of firewood, landscape staples, flower pots, children's toys.