I’m wondering if it’s best to up pot container trees/fruit bushes that go dormant in fall or early spring? Is there a better chance of winter survival for container plants if you up pot before temps drop so the soil acts as an insulating layer for the roots? If so, should you purposefully up pot close to freezing so the plant doesn’t have time to more actively grow roots? Or, will the excess soil just promote root rot in winters that have yo-yoing freeze/thaws? Transplant summer or early fall so the roots can get more growth in before freeze?
And, my impression from other threads is the best approach to winterizing is rolling the dice and not doing anything other than putting the containers against the house with extra mulch and maybe bags of mulch packed against them. The rootball will freeze where I am, but I should expect the plants will survive when thaw and not get root rot? What is the smallest container size to risk with that approach? Should fabric bag container plants survive as well as those plastic? All up potting and winterizing advice welcome!
I have gotten more laissez-faire about my containerized plants over the last few years. At first, I moved them inside all winter because I was afraid even a hard freeze would damage them, then I realized I could bury them in the ground and they’d do fine. But for the last few years I have left pots (1-5 gallon mostly) of woody seedlings above ground in or beside a plastic low tunnel with a bit of mulch around the base. This worked well until last winter. I ended up losing a potted hazelnut seeding and having 50% dieback on another, and most of my other plants sustained enough damage to not leaf out until two weeks ago. It wasn’t a much colder or longer winter than usual, but the fall and early winter until the end of January was so dry that I had to water things a few times and I think the drought stress made everything less hardy. If I’d buried them, they would have had better access to moisture as well as insulation. So, I’m going to go back to burying things this winter.
Most of my garden is orchard, but I have a small annual vegetable area, so I dig it up in December, after everything is dormant but before any very cold (-6C/20F) nights, and put the pots in and throw a few inches of leaves and a piece row cover over it. It’s usually enough to keep them from freezing and I’ve had potted lemon verbena survive this method.
I don’t think up potting will provide much additional hardiness, but if you do decide to bury them, then I would up pot before that since that will give the roots more space to grow over winter.
I think its critical to make sure the containers are well watered going into the winter. When you upshift the smaller container it can dry up inside the new pot if it isn’t rooted out into the new soil.
I grew nursey stock so we kept ours under poly in houses. We also left some above ground outside, jammed, exposed to the elements, if they were tough. We always watched the material under poly for dryness and would break out the hoses if they were dry.
Freezing and thawing is a drying out process. Moisture forms into ice, towards the surface and evaporates. Watering frozen pots or balls will do nothing. It’s a big issue on balled trees. People install them late, sometimes frozen and the balled tree can’t accept water. So when it thaws its dry. Usually they dont even get watered as the hoses are frozen. Bad scenario.
As for insulation I don’t think it hurts. I once potted a 1000 sweet 1 gal Palabin lilacs into 3 gallons thinking they would benefit from the upshift late in the season. The next spring they were all dead. I think the one gallons dried up over the winter. Maybe someone didn’t water them properly. Maybe the one gallons were dry when potted and they never really got wet enough being so late and going into polyhuts.
I think the key to getting anything through the winter is to make sure they go to sleep when they should, and go into the winter well watered. Also any protection from extreme swing in temps.
The ground contact provides more warmth than you might think. Containers on a deck, bench, or concrete slab are much more exposed. We would jam all the pots together when possible.
As Bakeapple stated getting them down in the ground offers the best protection. If you dont have too many. Or mulch them in.
This is generalized for standard stuff. There are always special needs for special plants and situations.
Thank you all this is really helpful! @JAF I had no idea of the evaporative/drying effect of freeze/thaw and the importance of making sure they’re well watered into winter. Sounds like, don’t up pot things in the fall? Thanks for the note about the ground because I had been debating whether to put them directly on ground or on cardboard/some sort of insulating foam block would be better.
I wish I could bury my pots, but I don’t have the space…although, @Bakeapple mentioning your vegetable garden makes me realize I could put my 1-3g plants in my raised vegetable beds! I cover everything with leaves, but they usually blow off to some degree. I will staple down burlap this year. Do you think I could put the burlap right over the plants? Or make cut outs for where the plants are? My smaller containers are grafted fruit trees, blueberries, pomegranates, raspberry. And some herbs and I plan to overwinter peppers this year.
I had originally planned to build a small 6x6 pvc frame against the cut out stairwell of my house and cover it in plastic/pack something around as insulation for 7-10g trees. But, the little I’ve found on here says to just let them be outside. So, I was going to go with the less-work approach first.
Aside from the pomegranates, I think if the containers are grouped closely and covered with burlap and leaves as you described it will moderate the freezing and thawing a bit and you’ll probably be fine. If you use the burlap, the cutouts for the tops of the plants will help them not break under the snow, but the sun and wind will increase desiccation, so I guess that depends on how snowy and wet it is. You could also lay them sideways and partially bury them. If it were me, I’d sink them upright into the raised beds and cover at least halfway up the pots with soil, then leaves and burlap with cutouts for fragile plants. However, we can get week long periods below freezing in the winter and the soil will often freeze 6 inches deep. It’s probably warm enough where you are that that is less of a problem. The pomegranates might get damaged if they aren’t really well covered, though. I’ve read that containerized plants are 2 zones less hardy than in the ground and I think it’s true because I usually get 50% winter kill on most unprotected zone 5 plants in containers here.
ETA: Also, I would bury the grafts on the small trees. I lost a persimmon from not doing that one year.
That’s not really an issue if everything is watered properly.
It’s also important to try and moderate the temperature swings. When its -15 outside at night, the air temps is -15 in a poly hut at 3:00AM. The polyhut offers protection from a rapid freeze and slows the process down and eliminated wind moving in the pots exchanging the air around them. Rapid changes are bad.
We would take our container trees 7 gallon to 25 gallon all varieties, and lay them down orderly on each other in a slant. Then cover them with a white frost cloth (like a spun landscape fabric) and then a layer of white poly. The frost cloth kept the poly from direct contact with the trees but mainly offered protection from temperature swings, as the cloth kept the sun from heating up the trees and ground below too rapidly. We lost very few trees using this method.
In a perfect situation, the pots would slowly get frozen or close, and stay frozen or close, and hopefully, the poly would get covered with a great insulator called snow. Elimanating the swings in temps under the cover.
Of course the trees were always well watered first. I’d tell them to water them really well, and when they told me they were finished, I’d tell them to water them again. You should also protect them from mice, rabbits, voles, and raccons as you created a nice microclimate full of food. We did thousands of trees a year this way for 25 years, and as far I know, (I retired), it’s still standard procedure.
Thank you so much. Really appreciate your thoughts and advice. I think I can cover the containers entirely since the raised beds are 17” tall. I never would have known about covering the graft site!
Wow, thank you! Really amazing info about the effect of rapid temperature changes for me to digest. Thanks for talking about how you would winterizing, I think to some degree, I can replicate that.
One more question- if everything is all wrapped up, then they wouldn’t be getting watered by snow or rain? Would you unwrap to water or have an irrigation system? Or is it not necessary to water every few weeks or month?
If they are completely closed off, then yes you will need to check them. Its really weather dependent. A weird January may be of concern. 60 for a week or two etc… if it stays cold its not such a concern. Freezing and thawing dries them out.
If you have them under closed poly you will probably be ok, but need to check on them once and a while. Water if needed. The big piles we had would hardly ever need water. It was a big issue to uncover and recover in the winter. Snow and ice on edges would make it impossible.
Come March 1st we’d look at the long range forecast, and if no severe weather, we uncover, stand up, and hopefully they get some rain or snow. If dry, we will fire up the hoses as the irrigation system has been winterized.
If exposed to weather then usually you have no worries.
OK, I will keep all of this in mind. Last winter when it became cold, it stayed cold, and we had a decent amount of snow that lingered. But, that was really atypical compared with the prior 10 years of yo-yoing temps from 20-60, isolated snow storms and 40+ temps right after snow so quick melts. I’m grasping from what you said that those are the winters I need to be most mindful with the containers.
