Juniperus scorpularum

Overwintering Bonsai in the Toronto Area USDA Zone 5-6

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I’ve received quite a few emails from people asking about overwintering hardy trees outdoors. While there is lots of good information out there on the internet, most of it is region specific. What applies in England, Japan, or North Carolina does not apply in Toronto. With that in mind, this information is specific to zone 5-6 and is for people who have no special facilities (heated garage, polyhouses, etc.).

Reiner Goebel of rgbonsai.com has a good article about overwintering trees in the Toronto area. Have a read here. What I do is very similar.

  • Use tough species to make life simple. Semi-hardy species (Trident maples etc.) require more attentive care in this climate. My collection consists of Eastern White Cedar, Larch, Juniper, Yew, Siberian Elm, Potentilla, Ginkgo, and  few others. All fully hardy.
  • Don’t be afraid to leave them on the bench through a few late autumn frosts. They can take it. I usually put mine away in late October or early November. If the ground is frozen, you’ve waited too long 🙂
  • Bury the pots in the ground in your garden and water everything really well. This insulates the roots. The risk is not the rootball freezing. It can and should freeze solid. The tree will be fine. The risk is frequent freeze-thaw cycles. This is why unusually warm winters are more of a concern to us northern bonsai growers than unusually cold ones. Burying the pot helps ensure that once the rootball freezes, it will stay frozen until around March, even if there are some freakishly warm days in January (it happens). If your tree is in a massive training box but is a hardy species, just sit it on the ground and mulch around it. Just having contact with the ground will help buffer the rootball temperatures.
  • Snow is your friend. As soon as fluffy snow hits the ground, shovel it onto your trees (don’t shovel on heavy wet snow!). Sure, three feet of snow can bend branches but I feel most comfortable when my trees are buried in snow all winter. This protects from -20 degree air temperatures and drying winds. But when the snow starts to melt, brush it away as this heavy slushy mess can really cause damage to branches and fine ramification.
  • Try and winter them in a shady spot in the garden protected from the wind (i.e. a north facing corner). This provides a bit of insurance against wind and sun if it is a snow-less winter (like the infamous winter of 2011). It also helps keep the tree dormant as far into the spring as possible. This is important. If your trees break dormancy too early, the tender new growth will be exposed to the unpredictable early spring weather.
  • Rabbit-proof your garden as best as possible. When rabbits get hungry in the winter, bonsai bark apparently looks quite appetizing. Even  a couple of exploratory nibbles can ruin the image of a tree. Try to board up any gaps under the fence.
  • If you have the energy, fence in your trees with hardware cloth to provide further protection from pests. Burying the fence a couple of inches provides me some reassurance against mice, although if mice want to get anywhere bad enough, they will find a way.
  • Don’t worry about watering! If you put them away late enough, they should not need any water the entire winter.
  • Again, keep them dormant as long as possible. Don’t take them out of the ground at the first sign of spring in March. You know that in our part of the world it is not impossible to have freezing nights in May, and these spring freezes can kill off tender new deciduous growth.

This approach has worked well for me for 8 seasons. There are many ways to do it, but I find this to be the simplest and most foolproof approach. It takes some time to prep the trees for winter, but once they are in the ground you can literally forget about them, sit back, and wait for repotting season to come! Unfortunately, since the trees are frozen solid in the ground, you cannot really work on them in the heart of winter.


Rocky Mountain Juniper First Styling

This slender Juniperus scorpularum was collected in the Kootenay region of British Columbia in 2009 by a friend. The last 3+ years leading up to today were all spent developing the pre-bonsai. The tree was probably strong enough for work in 2010, but lacked the foliage density. So, after three years of pondering, branch selection, and cutting, I felt today was the day for the first real work.

About a month ago I featured this tree on my blog where it was prepped for todays work. That cutting one month ago paid off as it produced backbudding which gave me lots of new fine branches to work with.

    Today before work. Its amazing how much things can change in a month. Sometimes NOT weeding your trees has its benefits! The plants that overtook this pot are identical to those growing in a large patio planter right next to the juniper. Its as if they knew this juniper was growing in a hanging planter!

Today before work. Its amazing how much things can change in a month. Sometimes NOT weeding your trees has its benefits! The plants that overtook this pot are identical to those growing in a large patio planter right next to the juniper. Its as if they knew this juniper was growing in a hanging planter!

    Petunias and Thai Basil were the most interesting 'weeds' that had established themselves in this pot.

Petunias and Thai Basil were the most interesting ‘weeds’ that had established themselves in this pot.

 

    The Thai Basil ended up in the vegetable crisper - everything else was compost.

The Thai Basil ended up in the vegetable crisper – everything else was compost.

    Front after work. Lots of foliage was removed... probably almost 90%. The tree will probably throw lots of juvenile foliage in response to the heavy cutting. The balance of this tree is unusual. The tree leans heavily to the left, and the key branch thrusts out to the left. Although the overall movement is to the RIGHT! I think?

Front after work. Lots of foliage was removed… probably almost 90%. The tree will probably throw lots of juvenile foliage in response to the heavy cutting. The balance of this tree is unusual. The tree leans heavily to the left, and the key branch thrusts out to the left. Although the overall movement is to the RIGHT! I think?

    Fresh of the mountain in June 2009.

Fresh of the mountain in June 2009.

 


Prep Work on Another Juniper

This is a Rocky Mountain Juniper (Juniperus scorpularum) that was collected in the Kootenay region of the Canadian Rockies back in 2009. Although slender it has nice movement, great deadwood details, and lots of branches.

Aside from maintenance pruning and wiring down some primary branches, this tree has never been worked in detail. Today I cleaned the bark, worked on some deadwood, and cut back quite a bit of growth in preparation for its summer styling. Preparing a tree for styling is almost as important as the styling itself. It has taken three years of cultivation and menial work to produce what is now almost a pre-bonsai. It is a long road from fresh yamadori to having something that is ready for bonsai work.

In terms of styling, this tree still has me scratching my head. The main problem is that the view of the trunk with the best movement and lean does not show the lovely natural shari. I will have to make some compromises when styling this tree… either in deadwood, or trunk movement.

Before work.

After work. My favorite view of the trunk… but the shari is at the back.

Another view showing the shari.

Possible front, although the top half of the tree is leaning strongly to the back.