All over Cape Cod, Hydrangea lovers are looking at the forecast for the night of March 21st and 22nd, and wondering if the twenty-degree temperatures are going to harm the buds on their Hydrangeas. After last year’s Polar Vortex, which caused most of these shrubs to die back to the ground and have fewer flowers, we are undeniably concerned about damage to our signature plant this year. Here are our thoughts:
Hey there, fellow garden enthusiasts! I’ve been growing hydrangeas for years, and one of the most common questions I get is about temperature tolerance. Let me tell you everything you need to know about keeping these beautiful bloomers happy in various temperatures
Quick Answer
Hydrangeas can generally tolerate temperatures between -30°F to 95°F depending on the species. However, their flower buds are more sensitive and can be damaged by late spring frosts or extreme heat.
Different Hydrangea Types and Their Temperature Tolerance
Old Wood Bloomers
- Bigleaf hydrangeas
- Oakleaf hydrangeas
- Mountain hydrangeas
These varieties can handle temperatures down to -15°F for the shrub itself, but their flower buds are super sensitive. Trust me, I learned this the hard way! One late frost can mess up your whole blooming season.
New Wood Bloomers
- Smooth hydrangeas
- Panicle hydrangeas
These tough cookies are my go-to recommendation for colder regions. They’re like the superheroes of the hydrangea world surviving temperatures as low as -30°F! Plus if frost damages them, they’ll still bloom on new growth.
Signs of Temperature Damage
Cold Damage Symptoms
- Wilted leaves turning red or purple
- Crispy, dry brown/black leaves
- Blackened flower buds
- Dried out buds
Heat Damage Symptoms
- Drooping leaves even when soil is moist
- Crispy brown leaf edges
- Faded or burned blooms
- Stunted growth
Protection Tips for Different Temperature Extremes
Cold Weather Protection
-
Mulching
- Apply 8-12 inches of mulch in late fall
- Cover root zone completely
- Use organic materials like straw or leaves
-
Winter Wrapping
- Use burlap or frost protection fabric
- Wrap plants when temps drop below 32°F
- Remove covering during warm winter days
-
Container Plants
- Move indoors when temps hit 45°F
- Store in cool, dark area
- Water occasionally during winter
Hot Weather Protection
-
Shade Management
- Provide afternoon shade
- Use shade cloth if needed
- Plant on east side of buildings
-
Watering Strategy
- Water deeply in morning
- Add extra mulch to retain moisture
- Monitor soil moisture daily during heat waves
Special Temperature Considerations
Spring Frost Protection
During spring, when we’re seeing temps bounce around like crazy (looking at you, Cincinnati weather!), keep these tips in mind:
- Watch weather forecasts carefully
- Cover plants temporarily when frost threatens
- Water well before expected frost
- Remove covers promptly when temps rise
Summer Heat Management
With summer temps hitting the 90s (like Cincinnati’s current forecast of 93°F), here’s what we do:
- Increase watering frequency
- Add extra mulch
- Provide temporary shade
- Avoid fertilizing during extreme heat
Hardiness Zone Recommendations
| Hydrangea Type | Minimum Zone | Maximum Zone |
|---|---|---|
| Bigleaf | Zone 6 | Zone 9 |
| Oakleaf | Zone 5 | Zone 9 |
| Panicle | Zone 3 | Zone 8 |
| Smooth | Zone 3 | Zone 9 |
| Mountain | Zone 6 | Zone 9 |
Pro Tips from Experience
- Don’t panic if your hydrangea looks dead after a cold snap – wait until spring to assess damage
- Avoid planting tender varieties in low spots where cold air settles
- Consider microclimate effects in your garden
- Group plants with similar temperature needs together
Common Mistakes to Avoid
- Removing winter protection too early
- Forgetting to harden off plants in spring
- Overprotecting hardy varieties
- Ignoring weather forecasts
Final Thoughts
Temperature management for hydrangeas isn’t rocket science, but it does require attention and care. I’ve killed my fair share of plants learning these lessons! Remember, different varieties have different needs, and local conditions play a huge role in success.
The key is to know your hydrangea type and your local climate patterns. Here in Cincinnati, we’re dealing with some pretty wild temperature swings – from winter freezes to summer heat waves hitting 93°F! But with proper planning and protection, your hydrangeas can thrive through it all.
Would you like me to explain anything in more detail?
The length of time that it’s so cold…
Although there hasn’t been much research about cold damage and Hydrangea flowering, there have been studies on spring cold and fruit trees. These studies show that the longer the cold period, the more flowers are damaged. I would expect that we might see something similar with our Hydrangeas. It could be that some of the buds on our shrubs will be zapped, while others survive.
Don’t be too quick to assume they are dead!
Your plants might have some buds that look black and lifeless after Thursday night’s temperature plunge, but don’t be hasty in thinking that there is no life there. The prudent thing to do is to wait until well into May to make the call about bud life or death. Some of the buds might have their outer leaves damaged but the inner buds may be alright. So wait to do any pruning until the second or third week of May.
What temperature is too cold for hydrangeas?
FAQ
At what temperature should I bring my hydrangea inside?
If you are growing hydrangeas in containers, bring them inside after the flowering season as soon as temperatures dip below 45°F degrees. Place them in a cool, unheated, dark, and dry place like a garage, basement, or mudroom.
What is the 1 3 rule for hydrangeas?
There are certain instances when pruning Hydrangeas can be helpful: All dead stems should be removed from hydrangeas every year. After the plants are at least 5 years old, about 1/3 of the older (living) stems can be removed down to the ground each summer. This will revitalize the plant.
Can I leave my potted hydrangea outside?
Choose frost resistant containers and you can leave the plants in the pots outside. The leaves will die off, the soil will freeze and the shrub will become dormant just like any hydrangeas in the ground.
Can hydrangeas tolerate a freeze?
Smooth and panicle hydrangeas both bloom on new growth and are both hardy all the way down to Zone 3, so they fare well in cold winter temperatures. If you live in a climate with freezing winters, you may as well play it safe and protect your smooth or panicle hydrangeas.