Plants
Hydrangea planting zones
Hydrangea covers 3a–9b, but the zone is only half the answer. Of the 7 types below, 4 carry their flower display through the spring freeze window and 2 do not, with 1 that does both. That difference decides whether a late freeze costs you a season of flowers.
The types
Which hydrangea you are choosing between
| Type | Zones | A late freeze |
|---|---|---|
| Bigleaf hydrangea Hydrangea macrophylla | 6a to 9a, then too hot | Exposed The mophead and lacecap types. Buds set the previous summer and stand above ground all winter. |
| Mountain hydrangea Hydrangea serrata | 6a to 9a, then too hot | Exposed Like bigleaf but with tougher buds; the usual recommendation where late freezes are routine. |
| Oakleaf hydrangea Hydrangea quercifolia | 5a to 9b, then too hot | Exposed A US native. Buds overwinter, but the plant carries autumn colour and bark when flowers are lost. |
| Climbing hydrangea Hydrangea anomala subsp. petiolaris | 4a to 8a, then too hot | Exposed Slow to establish and slow to flower; a lost bud year is a longer setback than on a shrub. |
| Panicle hydrangea Hydrangea paniculata | 3a to 8b, then too hot | Safe Flowers on the current season’s growth, so it blooms after any spring freeze has passed. |
| Smooth hydrangea Hydrangea arborescens | 3a to 9a, then too hot | Safe Also a US native, also new wood. Cut to the ground in spring and it still flowers that summer. |
| Reblooming bigleaf Hydrangea macrophylla (remontant) | 4b to 9a, then too hot | Partly exposed Bred for this problem: the overwintered flush can be lost and a second sets on new growth. |
Zone ranges and bloom habit are a judgement — horticultural convention, not a measurement, and the same standing as the heat ratings on our crop tables. Everything below this panel is measured.
Zone by zone
Which hydrangeas are hardy where, and when the freeze lands
The two left columns come from the variety table above — a judgement. The two right columns are measured: they are the median last spring freeze across every NOAA station the zone’s ZIP codes actually cite, and how much later the one-year-in-ten freeze arrives.
| Zone | Hardy here | Flowers exposed | Last spring freeze | 1 year in 10 |
|---|---|---|---|---|
| 3a | 2 of 7 | none | only 10 stations — too few to publish a range | |
| 3b | 2 of 7 | none | May 12 – May 30 across 92 stations | about 14 days later |
| 4a | 3 of 7 | 1 | May 6 – May 27 across 298 stations | about 14 days later |
| 4b | 4 of 7 | 1 (plus 1 partly) | May 2 – June 1 across 477 stations | about 14 days later |
| 5a | 5 of 7 | 2 (plus 1 partly) | April 28 – May 31 across 718 stations | about 14 days later |
| 5b | 5 of 7 | 2 (plus 1 partly) | April 22 – May 28 across 752 stations | about 15 days later |
| 6a | 7 of 7 | 4 (plus 1 partly) | April 18 – May 24 across 1004 stations | about 16 days later |
| 6b | 7 of 7 | 4 (plus 1 partly) | April 11 – May 19 across 991 stations | about 16 days later |
| 7a | 7 of 7 | 4 (plus 1 partly) | April 5 – May 9 across 941 stations | about 17 days later |
| 7b | 7 of 7 | 4 (plus 1 partly) | March 30 – April 26 across 679 stations | about 16 days later |
| 8a | 7 of 7 | 4 (plus 1 partly) | March 20 – April 16 across 689 stations | about 17 days later |
| 8b | 6 of 7 | 3 (plus 1 partly) | March 7 – April 17 across 700 stations | about 19 days later |
| 9a | 5 of 7 | 3 (plus 1 partly) | February 15 – April 6 across 446 stations | about 22 days later |
| 9b | 1 of 7 | 1 | February 2 – April 6 across 218 stations | about 27 days later |
“Hardy here” and “flowers exposed” are a judgement, from the variety table above. The freeze dates are measured — NOAA 1991–2020 climate normals, and the range is across the stations the zone’s own ZIP codes cite rather than one station chosen to speak for it.
Why the date matters
Your zone does not tell you your last freeze
Across the 13 zones above that publish a range, the median last spring freeze varies by 34 days inside a single zone — 18 days even in the tightest, zone 3b, and 63 in the widest, zone 9b. Two gardens with the same zone on the label can be a month apart on the date that decides whether hydrangeas flower.
And the median is not the risk. Across the 6,175 NOAA stations serving these zones, the freeze that arrives one year in ten lands a median of 16 days after the median date, and 22 days after it at the tenth of stations where that tail runs longest. A variety marked exposed above is standing in front of that whole window, not in front of one date.
⛔ We publish no temperature at which a bud is lost. NOAA’s normals give dates, not damage thresholds, and inventing a number to bridge the two is the one thing this site refuses everywhere else. What is on this page is when the freeze arrives and which flowers are out when it does.
Your ZIP code
Get the exact answer for your address
Everything above describes hydrangeas across the United States as a whole. Hardiness zones and freeze dates are published per ZIP code, so yours is exact — enter it and this page will tell you your zone, which NOAA station it comes from and how far away that station is.
Related
- Magnolia planting zones — 6 types, 3 of them exposed to a late freeze
- Dogwood planting zones — 5 types, 2 of them exposed to a late freeze
- All plant guides
- What survives my winter — the same zone arithmetic over 74 perennial edibles, which is a separate table from the one above
- When to start my seeds — the spring calendar anchored on the same measured last-freeze dates
- Your hardiness zone is not a planting date — the whole dataset behind the spread quoted above