My recent visit to see the junipers near Carson Pass, California, reminded me of the last time I saw these trees in October (see “Sierra junipers in the snow” for details). The trees had just been covered in snow and ice after the first storm of the season.
Sierra juniper after first snow – October 20, 2017
The weather is currently mild in the mountains but there’s a heat wave in the Bay Area with the temperature reaching 34 degrees C (93 degrees F) in my garden yesterday.
Such heat this late in the growing season forces me to adjust my schedule for when I do fall work. Until the temperatures cool down, I’ll treat my trees like it’s still summer and focus on watering and fertilizing.
Meanwhile, I know that in many parts of the country people are preparing their trees for winter storage. This isn’t an exercise we experience in the Bay Area so I’d love it if you can share your experiences, dos and don’ts, or any tips you have for people whose trees require protection in winter.
Depending on the feedback that comes in, I’ll look to do a post on the topic. You can leave your suggestions in the comments below, or email me directly (see email address at the bottom of the page).
In the meantime, here are two more photos from that October day three years ago.
Sierra juniper growing against a rock
Deadwood on a Sierra juniper, aka grand juniper (did you know Sierra junipers, formerly Juniperus occidentalis var. australis are now known as Juniperus grandis?)
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James Horine says
I keep a lot of trees in my garage. When I first started out it was not much of a problem as you could just shoe horn the trees in nice and tight with no problems. As the years go by and I had more fully wired trees I found they take up a lot more space in the garage then they did before they were styled/wired. That meant something was going to have to go out side for the winter. I did move a few things outside but decided that was not going to work for most stuff as I am to chicken to take the risk. I have come up with several ideas that seem to be working out good. First I purchased 6 foot plastic tables. I place one plastic table on top of another plastic table. I now get 3 times the floor space then I did before. More trees can stay in the garage. Small to medium size trees go under the tables and on top of the first table. Tall trees go on the top table. I also learned to place a piece of wood under the legs of the table sitting on top of another table. The weight of the trees on the top table will eventually punch (legs) a hole in the top of the table below it. I also came up with an idea of using cinder blocks stacked on top of each other to elevate wired trees above trees that can be shoved together for the winter. This new idea is working out great. Cinder blocks are cheap to buy. A neighbor was throwing out a couple of cheap plastic tables and I rescued them. They are working out ok so far, this is the first year for them. Anything tall will work in place of cinder blocks. Cascade trees go on the top tables.
You do want to avoid the freeze and thaw cycles on your trees. Wind is your worst enemy as it will dry them out in a hurry and kill them depending on the species. Not all species can be kept outside in Colorado and would I put them in my garage. Conifers will do just fine in your garage with no light. Or you could put in a fluorescent light if you want. You can also use a seedling heating pad in a garage to keep roots warmer on trees that might be somewhat iffy or may not be well to help them survive the winter. Nursery container trees can be kept outside in a protected place out of the sun and set directly on the ground. Build a wall around the trees with bales of straw one bale high. Level the pots off and insulate the trees with fallen leaves shoved very tightly in between the pots and straw bales. Add leaves to the top of the pots. Remember to water these trees during the winter. This is only for cold hardy nursery stock. Does not apply to Cotoneaster, Sage, or Sage type plants. Be sure to move these trees out into sunlight when they break dormancy. Failure to do so will result in long leggy branches and probably die sometime latter.
I generally have them all put away for the winter when the temps start to get into the single digits. I did move two thirds of my trees into the garage during the early snow fall. They are now all back out side and the tropical’s are in the house until spring. Garage housed trees also present a problem in spring because some start to bud out way early. These trees will have to be moved outside during the day and back inside during the night time. Wise planning on your part will position these trees close to the front garage door instead of in the back of the garage making it difficult to get to them. Another thing to consider is to install some “small gravel” bunkers where you can simple sink your trees into it in the fall and not worry about timing it just right. I have left my bigger conifers buried in the gravel bunkers all year. Watering trees in the garage is very important as they will dry out and die if not watered. Group trees that need more water together someplace you can get to them with out emptying out the whole garage to water them. Trees on heating pads will need a lot more water and will dry out quickly leading to death.
Lars Grimm says
Every climate offers unique challenges. In zone 7 here in North Carolina, we can get early freezes before leaves have even started to change colors in November, similarly we can get late freezes after everything has leafed out in March/April. I made the mistake in years past of storing shohin in a shed to keep them from getting too cold at night, but then the daily temps would heat the shed to over 70 degrees. I have found that shade is my friend to try and minimize temperature swings.
John DeMaegd says
I’m in Northern Indiana, a zone 5. So here I’m watering with more attentiveness because of slowed growth and am starting to gather deciduous to be placed in there winter protection as they are starting to be bare. The conifers and everything else will eventually go into a cold greenhouse with an opaque covering for the winter slumber.
Brad says
I’m in Flagstaff, so lowest low usually -10 to -15F and windy. Small trees go under the bench, then cover the bench with poly sheeting and secure the bottom of the sheeting to the ground with rocks. Large trees get crammed in together, along with a few 5 gallon buckets filled with water, and surrounded with big rocks, both for latent heat. Dump snow over everything when it’s available and wait until spring. I haven’t lost a single tree this way, though repotting too early is another story…
As noted above, shelter from wind and direct sun is key. The latter is to minimize freeze-thaw cycles.
Jeff Smith says
Here is a link to a presentation I did for the Minnesota Bonsai Society. I live in Minneapolis. This has worked for me the last few years.
https://docs.google.com/presentation/d/1xFtQGyy74xWi9MY1kNZr55085EwefiKb5sHOjHya3Qg/edit?usp=drivesdk
Sam Hurlbut says
I live in south central WA. Winters can get show some sub-zero temps., but not regularly. Summers are hot and dry with some windy days. My trees go into a bark mulch bed after leaves have fallen. The pots are covered and some of the trunk.
The beds are located on the north side of my neighbor’s cedar fence. This provides some protection from the wind along with some protection provided by my house. This, also, means they are in full shade all winter, which moderates any solar powered freeze-thaw cycles.
I am thrilled any time we get enough snow to cover them.
Doug Zeeff says
Zone 7 North Carolina: I have a section of fence set up in the shade. Everything not tropical gets set on the ground under the fence. I then cover everything with a layer of leaves. I stretch a layer of heavy plastic (the kind used when you pour concrete) over the fence to seal in the humidity and keep out the frost. Using this method I only have to water once a week or less. The last thing I do is set several mouse traps under the plastic. I have over wintered Marigolds and Pepper plants with my trees too.
scott chadd says
We are in zone 7 at about 1300′ elevation near the South Fork of the American River in Northern California. Some say that Trident Maples cannot be left out in the cold. Over 30 years the temp. here has gotten higher and higher. The winters used to be in the low teens and now we don’t get into the mid 20’s. In any case all of our bonsai (with the exception of our sub-tropicals) stay outdoors all year long. We have never had a Trident suffer from cold damage.
For our clients in Reno and South Lake Tahoe where the night time low can be 10 degrees below zero we recommend keeping them in the garage. If that is not possible find a place that is out of the direct wind, place the bonsai near the wall, cover the pot with loose material (Akadama, Hyuga, Kanuma) and then bury the whole thing under a couple of feet of straw and cover that with a shade cloth and they are ok. Remember, the cold wind is your enemy.
Lars Grimm says
Do you get any problems with rain or snow pressing down on the trees? Or is it set up like tent to shed it off?
Trudy Anderson says
This will be my first year in Ohio learning to store trees for the winter. We lived for 40 years in Vermont where we had a minimally heated greenhouse for winter protection. We moved to Florida and sadly left most of the temperate trees in VT. now I have moved to live with one of my children in Ohio. My collection includes a spectacular Sierra Juniper, a coast redwood and too many topicals. This will be a challenge to provide appropriate care for all. I love the pictures of the Sierra Junipers you have shared. I’m hoping the winter rest will help mine be more vigorous.
I have shelves and lights in the basement for some of the topicals and plan to move the winter hardy trees to the garage once it is colder. We always kept the Chinese Elm in the cold greenhouse for the winter but I think an Ohio winter will be too cold for it so it is in the kitchen at the moment.
Zack Clayton, CBS Editor says
It depends where in Ohio. In Central Ohio (Columbus) we vary between Zone 5 and 6. I assume a half zone warmer for trees in pots so a zone 6 plant is going to get extra protection or go to my basement, Dormancy be damned. I use 4′ LED shoplights over my trees. They have low electric consumption and very little heat output. I generally have 12-15 thousand Lumens over each shelf. Yes, the ones in my office light up the backyard until they turn off at night. I keep tropicals in those big translucent bins from big box stores as mini green houses for humidity. Google Columbus Bonsai and send me an email and I can give you our winterization article. BTW, Asian elms are variable by species in cold hardiness, Google your species and be conservative.
John Nate says
I live in Wisconsin, Zone 5, where it can get kinda cold. The coldest I’ve personally experienced is -42F, at which point we no longer head to the beach! :-). I have an unheated garage for tree storage. What I did last year, is built a wooden box, approx. 4′ x 6′ x 6″. The bottom is cheap OSB board (a cheap type of a plywood type material), the sides 3/4″ x 6″ pine boards. I added legs on the four corners so that the box tipped to one corner. I drilled a hole in that corner, lined the box with plastic, and inserted a small PVC vent/plug in the hole so water could drain out while keeping water away from the OSB bottom. Next, I snaked a wire heater that is used to prevent roof dams from forming across the bottom, covered with a bit of dry stall, used to keep horse stalls dry. Next, I placed in my trees on top of the dry stall (juniper, boxwood, maple, dawn redwood) and filled the gaps between pots with more dry stall. I plugged the heating coil into a temperature controller purchased from Amazon, set to turn on if the temperature got below 34 degrees and off if it got above 40 degrees. I buried the sensor for the control unit just under the surface of the dry stall next to my favorite tree. I watered about twice a month, with the excess water draining into a pan placed under the drainage hole. All trees survived the winter so I’ll be repeating this this winter.
Vinod says
Zone 5b, Chicago. Tropicals go inside in October to a sunny window or grow tent. Sub-tropicals (Osmanthus, winter jasmine, gardenia, Yaupon holly) and hardy plants (Junipers, elms, cotoneaster, wisteria) stay outside but buried to the rim in our big deck planter till the freezes are deep enough and regular enough that they threaten to freeze the rootball solid, which can be in November.
After that the sub-tropicals come inside, ideally these need a cold (but not freezing), bright room where they stay dormant and healthy. I don’t have this setup, so they go in a sunny windowsill in the living room. Unfortunately this can force weak, spindly growth, but I have to live with it.
The hardy plants get buried in the front yard and covered in leaf litter. This has worked well for me. If I run out of room, I keep some hardy plants in a tub filled with leaves in the garage, but our garage can go down to the 20s so there is risk involved. Wisteria juniper can handle this, but some others can’t. Trial and error.
If I could have a cool, bright sunroom for my sub-tropicals and a cool, non-freezing garage for the hardy plants, I would be all set.
Iris Tio says
Winter storage is tricky since so much depends on the type of tree, size of pot vs tray vs black plastic nursery containers, add this to the climate zone and no one has a one-size-fits-all answer.
For my zone 7 in Western Washington, come early November, pretty much all trees in bonsai pots or trays, go into unheated translucent shelters, to keep it from the freezing temps at nights, cold wind and the nonstop rains. I only leave out the cold-hardy pre bonsai which are still in nursery pots, they do fine with our (limited amounts of) snow, placed against a west facing fence. Tropicals (bougainvilleas, lemons, geraniums and tropical azaleas) go to a heated greenhouse.
Bob Anderson says
I live near Vancouver, BC, Canada Zone 8. We get freeze/thaw cycles through winter with freezing weather that can last a few weeks; rain and occasionally snow (often a lot of it all at once!)
I avoid fall re-potting. In late October I put all my pots in the ground near a hedge in the yard. I dig holes to the depth of each pot; wrap a bit of drain cloth over the soil in the pot to keep out dirt and deter critters; and push the surrounding dirt firmly up to the pots. That’s it. They stay there un-attended until the end of March.
The ground takes a long time to freeze so this seems to moderate the freeze thaw cycle in the weather. I haven’t lost any trees yet. I have pine, shimpaku juniper, larch, trident maple, Japanese Maple and cotoneaster.
Ralph F. Maggio says
Here in New Hampshire USA, I have an unheated room in my garage with a small space heater and fan.
The fan circulates the heat, keeping it between 35 and 38 degrees and the air movement is essential to cut down on fungal issues.
Any freezing is not a “deep” freeze due to it.
Michael Levin, Owner of Bonsai West in Massachusetts, then offered the best advice ever. “Keep them dormant as long as possible”!
Ryan Huston says
Hi Jonas,
I just moved from Seattle to Ohio. In Seattle, I had very little winter protection required. Now in Ohio I live on a rental property with no garage nor outdoor electrical outlets to regulate temperatures. I’m curious about what the minimalist version of winter protection would look like. I can protect from wind and try to keep things shaded and insulate roots, but would the normal freeze-thaw be too harmful?
Thanks, I look forward to hearing your findings!
-Ryan
LanceMac10 says
I too am in NH, Ralph! I just use wire racks in a plastic enclosed porch. Not reliable snow cover and too many varmints outside. Seems to work fine for JBP and JM. Chinese Elms and Tridents don’t handle it well, however. Went to an overwintering seminar at New England Bonsai years ago presented by John Romano. He led of with “move to North Carolina”! Michael is correct, but once a tree sniffs temps around 40 degrees, it’s going to wake. I’ve not experienced any fungal issues due to overwintering.
John Lee says
Here in Britain we have had different problems in recent years. Rain and rain and more rain from late Autumn right into Spring.
If there is no room to bring the trees inside then root rot is a real issue as is condition of akadama which is deteriorating into mud which transforms into clay when the weather warms up. So much so that I am only using it for top dressing now.
Any tips on new planting media would be great.
Jonas Dupuich says
That’s a lot of rain! What other media have you tried? Am also curious if mixes with less akadama, say 30% for example, make a difference.
MC Graham says
Hello Lance & Ralph – I’m also in NH! (Had no idea there were so many bonsai growers up here).
I keep my trees in a cold greenhouse with a small heater on a thermostat to keep it just above freezing. Big trees in nursery pots are on the concrete floor, everything else is up on cedar benches. The challenge is to keep the deciduous trees from leafing out too early as the days begin to lengthen (in February) and the sun warms the greenhouse during the day. Last year I installed a 40% shade cloth on the inside peak of the greenhouse (snow load would collect on an exterior shade cloth), and although it slowed down the leaf-out, I was spending 2+months carrying maples out of the greenhouse during the day to harden off the new growth. This year, I plan to use a 70% shade cloth to try to keep everything dormant longer. I keep my larches outdoors all winter on a covered porch, including a larch forest that I’ve had for 12 years. So far everything has survived and thrived, more or less.
Robert Thatcher says
My procedures since 1996 around the Detroit, Mi and Asheville, NC areas are similar, but timing is a little different. In Detroit I put trees away for the winter about November 1 and got them out in the spring about April 1. It is about 3 weeks later in the winter in Asheville and 3 weeks earlier in the spring in Asheville. You have to do three things: protect root balls from freezing / thawing / freezing / thawing/ etc.; protect the tops from the wind and keep watered. I did all three by putting the pots on the ground, mulching with leaves and watering about once a month if there was no rain or snow. I usually put a low fence around the leaves to keep them in place. I put a black weed barrier cloth on the ground and set the pots on that. Some folks in Detroit used pits in the ground with sand in the bottom to bury pots. In the spring the leaves go in the compost bins. In the fall the compost goes in the garden.