Good morning everyone,
I live in Northern Va in a condo. I have a full south facing 6X20’ deck that I have 20+ outdoor bonsai trees and most of them are in small pots. I have watched last years Winterization Q&A 5 plus times and I’m confused. So I’m making a couple DIY greenhouse to protect the trees with small pots because the Q&A states that the roots need extra help maintaining safe temperatures. The bigger trees will stay out in the weather with some added protection ( mulch ). My confusion is, is this the right thing to do for the smaller potted plants. Will this harm the spring and summer growth, what temperature in the greenhouse is safe to maintain, I will treat the plants first before they go in for fungus (but how do I know if it’s present afterward), What would you do?
Thank you in advance!!
Victor
Hi @VICTOR,
Winter treatment of trees will depend on a lot of factors including what type of tree, what species of tree, what work has been done on the tree…
If you are expecting it to get too cold for your trees I would be looking to get them on the ground, out of the wind, close together, overhead protection, pots packed in clean bark - in that order. Lastly, keep an eye on them over the winter to make sure they find dry out completely and keep pests off.
@AndyK, I think we’ve got the same schpiel in the same order at this point! 
@VICTOR: exactly what AndyK said. If you want to specify what species of trees you’re working with, we can give you more help.
“If you are expecting it to get too cold …” Is there some rule of thumb for what temperature range a tree in a pot can tolerate without killing it? I realize it depends on many variables, but I’m wondering just how cold it can get before I should worry.
No rule of thumb I’m afraid @JohnH,
As you say, many variables- type of tree, size of tree, size of pot, recent work done on tree…
You could say protect all trees in freezing weather, but that would be wrong, as some species need freezings temperatures for dormancy.
I can honestly say that every winter I get it wrong with at least 1 tree.
Thanks for the reply. I live in northern VA and while we can have below freezing winter temperatures for extended periods, we rarely have sustained low teens or single digit cold. I don’t have a lot of trees and I usually put them in my summer tomato bed. Over the years doing that I’ve lost two trees, but this year I don’t have the use of that bed. So, I’m thinking about leaving them on the bench. I have a south east exposure, so get some protection from the colder winds coming from the north. The smaller trees I’ll put up against the house or put them in the garage. Thanks.
Hey guys,
do you spray your trees with sulfur before winter or better question, is it necessary to do this? At the moment all my trees are healthy and will be stored on a balcony, packed in mulch and protected from strong winds. I’m not really sure if i should spray them as prevention. Normally there shouldn’t be this much of fungus danger if the trees are stored outside, right?
Sorry for the delay in response. I have 2 Redwood seedlings (1-2 yrs old) in a ceramic pot. A few Apple tree seedlings in plastic pots, a few Maple seedlings in plastic pots, 2 Dwarf Chinese Elms in ceramic pots. a few pines in various pots. So in a nut shell it’s Noah’s Ark of young plants.
@Victor: I’d check the hardiness zones on the apple trees. All of the rest should be fine in your hardiness zone; just make sure to put them on the ground out of the wind and mulch densely up to the rim of the pot.
A good rule of thumb: for the trees you listed, you want to keep the trees’ roots above 28-32F. Pots on the ground that are out of the wind and mulched will stay much warmer (10F+ warmer) than the air. Smaller pots will get colder more quickly. You can always check temps with a thermometer if you need to. If it looks like you’re going to get a multi-day cold snap that could freeze your roots, bring them under cover until it warms up.
I’d like to add a question onto this post…I just built a wind shelter out of 4mil clear plastic for my evergreens. I bought mulch but it was soaking wet, I simply used dry leaves that were chopped up in my lawn mower over the fall to insulate my pots…is this sufficient? Also, I have this built half under an awning but it already got soaked in the rain today…is this a problem? Will wet leaves provide insulation?>we are getting a hard freeze tonight.
I have been winter storing my small deciduous trees on the ground, under my kiwi arbor for 22 years. I use plywood sides to stop wind dessication. When it hits<30 deg. F., I cover and work whole Norway maple leaves down to the pots to insulate. The top is open to rain and snow. When temps are scheduled to be <20 F, IF they are not covered with snow, I throw a tarp (with supports) over.
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Uncover / Remove trees as soon as it warms in spring…
Do Not forget to place mice poison in covered containers in several points… I lost trees to voles.
I’ve never had serious fungus problems. Sulfer sprays if needed in spring.
Not complicated. Pacific NW. Brutal winter sometimes. This works well.
Awesome, thanks Kurt! What do you put the mice poison in?
I use a cheap small covered Styrofoam soup bowl 3"?
Clip a v for access. Leftover from Xmas. But them I’m putting out a dozen. Didn’t lose trees last winter. Oddly, voles chew on evergreens, too…
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I also use my cinder blocks and 2x6x8 redwood benches to build a u storage against my garage. For evergreens. <20 F gets covered till >32 F. Snow is an insulater…
This bonsai thing seems to be taking over…
Yes, those are really big shore pines and Ponderosa!
I live in a condo where there is no ground, just a cement slab. I have sheltered them from the wind and somewhat from the weather. I will get a few wood or plastic boxes and protect them with mulch.
It snowed today and the temps will be around 37 tonight.
Oooh. I love little trees.
Just an idea…Make miny hothouse.
Keep it simple and clean. Try bubble wrap over top and 1" of styrefoam under to keep off cement… Once they are cold, keep them out of DIRECT sun. Some air circulation. Open when spring temps> 35.
Watch for dessication. Ice or snow cubes works… when they melt.
It was 22 F here last night. NOT worried yet! Wish I had some snow!
Good luck!