overwintering Hydrangea macrophylla winter protection
More than you wanted to know.
About this time of year, if you look in the leaf axils of new wood, you'll see a very small bud that might just be barely noticable. But, if it hasn't done so already, the ones at the tip of the cane and especially the ones toward the top of the cane will start to swell up and by the time frost arrives, these top most buds will be the size of a small bean. If you should be so lucky to get these buds through the winter and spring, then next year a cane will grow from these buds, a cane that could be a foot long with several pairs of leaves, terminating with a beautiful flower.
This comes from Michael Dirr's book, Manual of Woody Landscape Plants: Hydrangea Macrophylla and Serattas.
"HARDINESS: Zone 6 to 9, does not do well in Zone 5 unless extremely well sited, as one goes south and east this becomes a very common plant; however, in the northern states it is rare to see it in full flower; qualification is necessary for I have seen the plant in Urbana, IL withstand -20 F; it never flowered, but did come back from the crown to produce a respectable mound of foilage; since flowers are set (largely) on last year's growth, if the shoots are killed then flowering is history; I have seen the most magnificent flowering specimens on Cape Cod; in Zone 8, Athens, where the plant should prosper, 2 flowering years out of 3 might be considered good; the plant is soft and succulent and does not harden and the tops of the plant are killed."
The weather at Cape Cod is moderated by the ocean. For Cape Cod, the daily swing in the temperature might be 14 degrees, but for you and me it might be 21 degrees. In a week or a month it's the same thing. I remember going out to the beach in the late spring and realizing that it was downright cold out there. I think of the beach as hot because it's usually mid summer when I might go, but this trip woke me up to the realization that it's slow to warm up in the spring, and slow to get cold in the fall. Everything was late to bloom at the shore. I imagine that must be the kind of environment in which Hydrangea Macrophylla must have evolved in the islands of Japan.
"Roses can take hot, Roses can take cold. What they can't take is hot, cold, hot, cold...." I think of this when I'm thinking about overwintering my hydrangeas.
Even though we talk about overwintering hydrangeas, I think it's worth while to make the point upfront that the trickiest part of this whole business is the spring and you should pay really close attention to your plant in the spring. In my earliest attempts I would get the plant through the winter, only to kill it off in the spring. That hurts when you only get one chance each year. When your buds break dormancy in the Spring, it takes just the least amount of frost to zap them. They are sooooo tender. Don't forget.
I thought these were interesting comments make in this forum last Spring:
Posted by kars z7 LI, NY (My Page) on Sat, May 24, 03 at 8:47
I see many discussions on zones looking back through the forums. I am on the south shore of Long Island's east end, less than a mile from the water. We are considered zone 7. My mother lives about 30 miles west of me, towards the city and she is in the center if the island, about 15 miles from the south shore and 10 miles form the north shore. On any average winter day I am 5-10 degrees warmer than her. I even went and checked my thermometer against hers. Sometimes when it is snowing at her house it is raining at mine. Sometimes it is snowing north of me towards the north shore and raining by me. The norht shore gets the cold north wind, even though it is coming off the water (Long Island Sound)it changes the micro climate. That wind does not seem to effect me though. I've had days in the late winter when the wind is out of the north and changes to the south and the temps can change by 10 degrees or more. Plus the water seems to stabilize the temps.
Also the reverse is true for the summers. I often get comments from visiting friends that as they came within a distance to my house they had to roll the windows up cause it was chilly. This could be on a 70-80F day.
Posted by: fdutra 7 maritime (email@example.com) on Sun, May 25, 03 at 7:46
Botanically speaking, the "true" Hydrangea macrophylla is considered a maritime species, originating from the near coastal regions and smaller islands of Japan's eastern shore. Since nearly all garden/landscape macrophyllas are hybrids originate from this stock, it's not surprising that Long Island's near coastal regions have an advantage when it comes to raising hydrangeas. It's more than just the higher average winter temps that help with overall plant survival and bud hardiness. That +/-10 degree moderating affect from the ocean makes a big difference when it comes to early and late frosts. Seasonably cooler temps in the spring help to keep budding hydrangeas in check, often avoiding that late spring killer frost that often wreaks havoc further South and inland. When they are developing next years flowers in the fall, the warming effect of the ocean will offer some protection from an early frost/freeze. The cooling effect of ocean breezes in the summer, along with frequent fog and higher than average relative humidity doesn't hurt them any either. A few miles inland can make a big difference as you noted, so I guess I'll be staying with the old maps and their confusing micro climates out here on Nantucket.
Posted by: kars z7 LI, NY (My Page) on Sun, May 25, 03 at 11:44
fdutra - Good points. We usually do not get our first freeze until late December or later. Often not until January. Often when my mother wakes up to frost on the lawn I do not. This year my mother had snow in April but it was rain by me. A few miles north of me, farther inland there was snow on the ground. The temp stayed around 34 at my house. I am still amazed at how a mile or two can make a difference. There is a home on the bay that has a row of hydrangea at least 60 feet long. They look incredible in the summer. They seem to handle the winds and salt spray very well.
Ohh and that fog, many a night it rolls in around dusk and takes the morning sun an hour to clear it out."
I guess that is what we would like to duplicate if we want to get Hydrangea Macrophyllas to flower for us.
My most successful technique for overwintering is to either have the plant already in a pot (some in 15 gallon pots, some in less than a gallon.) or else I'll dig up the plant in the fall and use a 30 gallon size plastic bag which I don't open but instead just lay down as it is. I place the plant on top and tie the corners of the bag in a way that makes a snug enclosure for the root ball, the look of a balled and burlaped plant. I'll jab a few holes at the bottom for drainage. I think this is a better way than trying to put them into a pot. I wouldn't try this with an old, established plant, but it's easy enough for younger ones, and if you do it repeatedly, the root ball will stay tighter. Then I drive them out to my friend's house at the beach....If only, huh? I forgot... I use these same plastic bags to tie around the gathered up canes so that I have a more compact plant to deal with. Just like a piece of rope or twine, but less likely to cut into the plant.
I gather dry leaves and bag them in these same 30 gallon plastic bags. Next summer I can use the leaves as a mulch or a compost ingredient or keep them to use again. Many of them will get wet and some of these will eventually rot to nice leaf mold, right in the plastic bag. But for this winter, I'll use the leaf bags to make a corral by stacking them up. The old wet ones can go on the bottom. It doesn't need to be very tall, just enough to enclose these plants after they're laid down. Couple of feet, maybe. They might want to slip and slide, but you can lay some boards or limbs or something across a span of them to tie them all together. I do a lot, so I might end up with a space that's 15 feet by 6 feet by 2 feet tall.
I lay my plants down inside. I stack them and layer them some. I'm aiming for the sardine look. I usually put boards on top of the corral around the perimeter and then lay other boards across the top of everything trying to create a lattice over which I can spread one layer of these bags of leaves. Now I've got the plants laid down and enclosed by these bags of dry leaves. When it gets very cold later on, I will put a sheet of plastic over all this.
In the spring, I want to keep the plants inside this enclosure for as long as I can. I want them to stay dormant for as long as they can.
But at the point I bring them out, I hope that there is no forecast of a frost and hope that I have a good shot at not having another frost for the season. That's ideal. The plants will start putting out growth before I'd like to bring them out and this new growth will be your basic white with a tinge of yellow. That's what happens when they don't have any light at all. I can get a leafy stem that is several inches long. This is not a problem and the plant will do just fine even if I left it to grow inside this dark place. The real problem I have is that the plants are bound up and laying on their side. As this new growth comes in, it wants to go up, but since the plant is laying down, that's really sideways.Mabye I could deal with that, but since they're bound up, the new growth gets all entangled and when I unwrap it, it's difficult to untangle.
On the day I take them out, I check the weather forecast for as far as the eye can see. Just the kind of forecast you wouldn't want is what I want to see. We might have had a few nice warm spells, but I'm looking for weather that is on the chilly side but not freezing, wet and overcast. Don't run out on the first nice warm days of spring and throw everything off. ( If I could, I might throw more insulation on when we get those warm days). These plants need to be acclimated to the outside world and if you hadn't seen the light of day for months, you'd appreciate taking it nice and slow.
For a while, I'll leave them laying down, keeping an eye on the forecast. I might cover them with just a sheet of plastic if there is going to be a cold night. I've covered some that were in sunny location on some afternoons when it was very sunny, but last winter I had a group under some maple trees that leafed out just as I was uncovering them and the dappled shade was just perfect.
Mostly because they're growing sideways I'll feel that I need to stand them up and I'll look for a forecast of no frost for the foreseeable future. It never seems to work out that way and I'll need to lay them back down with a sheet over them . Remember that they're very, very sensitive at this point . One frost and they're gone. That being the case, I end up laying them down even if there is a threat of frost, meaning that I lay them down many times when no frost actually occurs.
Finally I think I'm safe and I'll untie and untangle them.
I think it's interesting that I don't get any rodent damage. They might dig into the soil, but I don't think I've ever seen a single bud eaten. The bark doesn't seem to be harmed. I've tried to overwinter other shrubs in this mound, and the bark gets peeled right off and the plants die. These plants show up on some poison lists. (I know, I know, the deer love them. What can I say? For me, I've never seen any deer damage either, but I know it's common. )
And it surprised me that plants can send up new growth even if there is no light. I've overwintered other plants in different ways and I've now seen this a lot. You bring a plant out into the real world slowly and it will green up and be just fine. Don't get all crazy thinking that because you've got all this white new growth you've got to get the plant out quickly. It's OK. I had a hydrangea in a dark cellar send up a white flower in March. I kept it down there for another month and it was still just fine after I slowly brought it out.
I make sure they go in well watered and they come out just as moist as they went in. Just like it's always damp around the ocean, that is a very damp environment they're in.
I have usually put my plants away before they've dropped their leaves. Other people's comments suggest that I put them in way to early, but that's the way I've done it. The leaves can end up pretty slimey before Spring and you'd think that all this mess couldn't be very healthful, but I haven't noticed any problem yet.
I've gotten very fond of using hydrangeas in pots. Big ones, small ones, whatever. They're great for a terrace plant. Start to Finish. I drop big pots and medium size ones in a border. A pretty pot is nice, but a black plastic pot will disappear to the eye. The pot gives them the extra height they need when they flop. And they're easier to overwinter in a pot. This mound is the best technique for me, but there are other ways that I've tried.
I've overwintered some in a cellar that wasn't really all that cold. It was dark. They did just fine. Being so warm, they broke dormancy in February, sending up white new growth and even a flower or two. I ended up with flowers lots sooner than otherwise. I think I'd like an environment a lot closer to freezing. I would imagine that the ideal might be right around freezing or lower. Once I tried overwintering some in an unheated, uninsulated room that got below freezing. The root ball froze and it seemed like the buds just sort of got freeze dried. I wonder if the plant would have survived a frozen root ball if it had been in a very wet environment like the ocean or under my mound.
I overwintered some in a crawl space that was insulated enough to keep exposed water pipes from freezing.
I've had pretty good luck overwintering them on the steps of a cellar leading in from the outside.
Somewhere you should be able to find a good spot around your property. Maybe an unheated, enclosed garage. Maybe you can lay one down along your foundation and put a couple of bags of leaves on top. Camoflauge it with a piece of burlap.
I haven't done it, but I bet you could mound a layer of shreded wood chips over them. Other people have had good luck using wood chips with ones they overwintered in the ground, so I can't imagine that they wouldn't work for a pot. Wood chips would be insulating, moist, and breathable.
I once saw some people talking in the Northern Gardeners forum about burying other plants in the ground for the winter. Would that work for hydrangeas? Might.
I wonder what would happen if you dropped a bound up plant into a big garbage can and then filled it with dry white pine needles. You could set this inside a garage maybe.
People all over suburbia are putting their bags of leaves out on the curb in the fall. Maybe they could stack a few around the shed out back or behind the garage or someplace like that to cover their hydrangeas.
Lay a few on their sides and cover with some chicken wire and then mound leaves over the top. That might work and a small pile of leaves around wouldn't be such an eyesore.
My very first technique was to basically do the same thing, only do it with the plant still in the ground. I'd get half filled bags of dry leaves. (Half because they were smaller and I could manipulate them better). When it's looking like the thermometer would be going down to below 25 degrees I'll insulate them. I think I do it too soon, but that's what I do. The leaves are still on the plant.
I will gather and tie up the canes so that I have a small column. With stout wire, maybe six feet tall, I'll make a cage around this plant leaving about a foot or more of space around the plant. I'll place these bags of leaves around the plant, turning them upside down so that water is less likely to get in to the leaves. I leave cracks intentionally so that the plant can breathe a little. At the top I usually lash down some bags.
In the spring, I slowly acclimate them out. Take off some bags from the north side. Then some on the south side. You don't need to take off the bottom bags until the very end, but be prepared to cover the plant back up if a frost looks likely. I leave it bound up until the very end and sometimes, after it's all uncovered, I've gone out and wrapped it with plastic or put a plastic bag over it or even an old blanket if it looks like a late spring frost.
My most ambitious project was to overwinter five very old hydrangea that were in an L with a fence on one side and a shed on the other. I bound up the plants, and then pressed them down as hard as I could to get them lower. Put a fence around to finish the enclosure and placed bags of leaves around. Lots of leaves. Finally I put enough loose leaves around and over them to create the impression of a bin of leaves. Not quite so ugly. It worked.
Many people do what I do with the wire and then just fill the space with loose leaves. I've done this a couple of times and failed. I packed them in much too tight once and the plant looked like it rotted. Last winter I used oak leaves because they're supposed to stay fluffy and dry longer but it was a record cold winter for us and they didn't make it.
I know many people have mentioned using wood chips. . That makes sense to me. I've seen people talk about using a trash can with it's bottom cut out and placed around the plant. Then they put wood chips in around the plant.
Here are some pictures for you. I'm linking so that those on a slow connection won't have problems waiting so long.
I'm tired of talking and I'm sure you're tired of reading.So, enough. Good luck.