Will The Cold Temperatures Kill My Hydrangea Flowers? (See update below!)
Will The Cold Temperatures Kill My Hydrangea Flowers? (See update below!)
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:
Some Hydrangeas are more bud-hardy than others.
Some varieties of Hydrangea macrophylla (mopheads and some lacecaps) and Hydrangea seratta (lacecaps) are more bud-hardy than others. So some of these plants will be better able to keep the buds that are currently on the canes, and have them grow and flower despite the freeze that’s predicted for Thursday and Friday nights. If you’ve had good Hydrangea flowering on some plants but not others in the past, you’ve seen this for yourself. I personally have seen that many of my newer plants such as Endless Summer, Enchantress, and Summer Crush have been more bud-hardy than the older Nikko Blue and Glowing Embers.
Location, Location, Location!
We all have seen that some parts of our properties are warmer than others. Since cold sinks, it’s usually plant in low areas that are more damaged by a plunge into the 20’s. So some of your plants might fare better than others depending on where they are located. Properties that are closer to the ocean also tend to be a bit warmer than those in the interior.
Can I throw a sheet or blanket over my plants?
Unfortunately, a sheet, blanket or tarp is only effective for protecting plants when a brief dip below 32° is predicted. Coverings like this won’t help when the temperatures are going into the 20’s, since there isn’t a heat source under the wrappings to keep things warmer. If you built a small greenhouse over each plant, and that was there to heat the soil for a few days before the dip in temps, that might help, but that’s unrealistic and for most people would be a waste of time and money.
Can’t I spray something on to protect those buds?
It would be wonderful if products such as Wilt-pruf would shield Hydrangea buds from cold damage, but unfortunately there is no such spray that will help.
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.
Optimism is always the percentage play.
Instead of getting upset, let’s all focus on the best possible Hydrangea season for 2024. Once we know how our plants made it though this, and possibly other challenging temperature swings, we can focus on moving forward. Watch this blog for future posts about Hydrangea varieties that will flower even after a hard-freeze winter, and know that we have much to celebrate in Cape Cod gardens no matter what trials Nature throws our way.
Update! The State of Hydrangeas, March 25th
Right now we have every reason to remain optimistic. Many of our Hydrangeas seem to have come through the deep-freeze of last week in good shape. Some of these plants that are less bud-hardy (the ones that you seldom see flowers on) might have been damaged, but most of the usually-planted varieties should be fine. However…we aren’t out of the woods yet! Sometimes we’ll have a dip into the twenties again in April. So remain hopeful. I, for one, am keeping “a prayer of protection” around my Hydrangeas until May.
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Thanks for this info. It was very helpful.
Thank you, helpful information.
We used to put a 100 watt light bulb under the hood of the car all night to keep the oil from thickening during cold snaps. Would a 100 watt bulb under a tarp or sheet do the same and protect freezing of the bud?
Perhaps – it depends if the tarp is large enough so that the wind doesn’t go under and just blow the heat away. Also, keep a light bulb off the ground and away from any dried leaves – you don’t want to cause a fire! Not to mention you’ll want to keep the fixture away from moisture, since most lights on cords are not meant to be in wet environments.
Thank you as always CL! I shared the link with the members of the Chatham Garden Club! And I now am ALSO getting Thank Yous from our members!
Agree — very helpful.
Is it a good idea to wrap the hydrangeas in burlap? I covered my hydrangeas with sheets , however the rain froze the sheets to the buds of the plant! I’ll wait till May to see what happens. I don’t know why I have trouble getting my hydrangeas to bloom. Guess I cut them back at the wrong time? This year I didn’t cut them, but with this frost, we will see what will happen. Any advice would be greatly appreciated. Thank you, Judy
Burlap doesn’t protect the plants at all. If you want your Hydrangeas to flower, never cut them back unless you see that the canes are clearly dead. They form their flower buds in July and August for the following year, so any cutting down takes those away. Also, those buds can get zapped by temperatures that fall much below 15 degrees. As I mentioned in the article, some Hydrangeas are more bud-hardy than others. Right now it’s looking like a good year for Hydrangea flowering as long as the plants weren’t cut back. But if you see that your plants don’t flower year after year, try some of the new varieties such as Let’s Dance Sky View, Let’s Dance Can Do, Let’s Dance Rhythmic Blue, and Pop Star.
i would like to keep an endless summer lacecap hydrangea in a planter outside on a north facing, second story balcony.
(i love how endless summer just keeps on blooming all season)
how do they do in that environment thru the cold winter and cold snaps in early spring?
do i need to keep the soil moist via watering thru the winter?
i was planning to cover the top with a layer of salt hay. good idea?
i have done this with a large hosta from last summer and watered it twice during the winter. (a good soaking)
we will see what happens this spring!
i am trying to create a hardy container garden for my balcony.
i really miss my former perennial garden so trying my best to recreate it on a balcony now.
any further recommendations are welcome.
thank you so much C.L. for your expert advice and suggestions!
You should be okay on a north-facing balcony if the area gets some direct sun either in the morning or late afternoon. There are varieties that might be better for you, however, that are also remontant (that means re-blooming) – check out Pop Star, Summer Crush (purple in acidic soil), Rhythmic Blue or Sky View.
thank you very much C.L.
apprec the suggestions.
i assume these varieties may do better in planters?
the balcony does not get any direct sun. it has roof. it gets bright indirect light all day though.
should i water planters over the winter at all?
i often wait for days w/ temps in 40s so soil is not solid frozen block.
thank you so much!
happy spring to you!
~ beth
Yes to the planters. Only water in winter if it hasn’t rained/snowed in three weeks and the temperatures are above freezing. Don’t water frozen soil.