Bonsai: Winter Care

12 year old Lilac (with pink Oxalis and mosses )  on a Natural Basalt stone 'pot'

Our loyal readers of  Incoming Bytes  know that  some  of my favourite distractions are gardening,  growing things, experimenting  with  apple trees,  and  bonsai.  Trees in pots.
 
When winter comes along, everything slows down,  so what, the leaves fall off,  stuff  goes dormant, and that's that-- we end up doing something else for a few months.  We contemplate, plan for next year, rearrange,  diddle, design, and optimize.  Where we live, ensuring our perennials survive the very cold winter of Northern Ontario is mandatory.

Because they are just potted plants, it is easy to forget  bonsai are real trees, however diminutive. Bonsai may be tougher than other potted plants, but winter comes for them too.

Why would we bother to winterize little trees when we know most trees are incredibly tough?  Their 80-foot tall relatives  take a beating, surviving  whimsical and unpredictable conditions, don't they? Don't big trees survive howling winds, freezing rain, snow and ice, attacks by mice, rabbits and deer alike?   Why would we need to 'store' bonsai when winter comes along? 

They may equally be trees, but the significant difference is:

• Bonsai grow in a very limited, even tiny amounts of soil, and  survive on  small amounts of nutrients.  They do not have unlimited soil under them.
• They have smaller root systems which are stressed more easily , 
• Swings in temperature including freeze / thaw cycles  within ceramic pots  are more rapid and extreme.  Hard freezing of moisture and expansion in potted plants can dislocate roots from the soil and break the pots too.
• There is less moisture reserve, so  small pots can dry out quickly, particularly in desiccating fall and winter winds.  
• Small trees, particularly apple, pear, cherry, maple and birch trees have sweet bark that may be damaged by foraging mice, rabbits or even  deer. 
• Foliage can be destroyed and compressed, branches can be broken by excessive ice and snow load,

 Extra care should be taken to protect valuable bonsai  during the fall and winter --and there are several methods that can be used to ensure your bonsai survive the winter with minimal damage.

Options include: 

• Move bonsai into a cool room in your home, a garage, or  green house. Hot, dry air in most homes  is undesirable. Turn down and control the heat in that area if possible.
• Store bonsai in a  "cold house"  (unheated greenhouse). Few hobbyists  can afford to have greenhouses heated year round,  so an unheated greenhouse is fine. Keep in mind the trees must be checked and watered regularly to keep the soil from drying out in dry winter air--particularly the smallest trees.
• Building a simple shelter roof over the bonsai display shelves.  This can be as simple as a narrow single- pitch roof over the shelf area  supported by two poles to protect trees from  heavy snow load accumulation.  Add a slatted wall on the  side the wind normally prevails from to protect your trees from brutal winter wind.  This method of storage is fine for larger trees which have larger soil volume and can withstand more severe weather. 

• In very severe climates, consider storing bonsai directly on the ground.   In North western Ontario, this method is my favorite.  It has been quite successful, with very few trees lost over 15 years. The method attempts to mimic the conditions a small indigenous tree would experience  growing naturally in the wilds. The dry leaf cover reduces soil drying, so once bedded down, the trees can essentially remain untouched over the winter. 

Here's what part of our collection looked like going into storage.  Note the pots are being placed directly on the damp grass. Pots are put shoulder to shoulder with no spacing, placing trees of similar size and height adjacent to one another.
The old  desk in the background is  part of Mother Nature's Bonsai School.

Bonsai pots being placed directly on the grass

 It takes a huge pile of leaves to bed this collection of over 150 bonsai pots.

Bonsai Collection tucked in winter bed  with dry leaves

The dried leaves are dropped on bonsai and tucked in under tree crowns where required.  Many  of the smallest trees are covered entirely with a couple of inches  of leaves.
 *Notice the Spartan apple tree sprout still has GREEN leaves on. For November 3, 2011, that is pretty amazing.  Young fruit trees can survive winter storage using this  method.  This Spartan  has survived winter  two years already and will be planted in the spring.

Here's what the same collection looks like after it froze and collected a few inches of snow.  In winters of heavier snow collections, only the tips of the very tallest may be seen.

Winter storage of bonsai. * Note the chicken-wire enclosure.

 Note the enclosure made of ordinary chicken-wire netting and some temporary steel posts that can be quickly and easily  removed from the lawn in the spring.

The only caveats that apply to this simple storage system are:

• If you live in an area where heavy, wet extreme snowfall is normal,  snow loads may break branches or deform crowns if they are thick and  not supported properly.   This method of storage is not recommended for extremely valuable old specimens in stages of advanced design.
• Non-indigenous species from warmer geographical locations are subject to frost damage, so should be in a warm environment
• If  bonsai are bedded too early they may not be dormant. *Ensure your trees are fully dormant with no leaves,  especially if they are small specimens that may be covered completely.
• Water the trees prior to installing the leaf cover with dry leaves. Do not soak down the leaves to minimize compacting and matting over smaller trees.
• Timing is important.  The ideal time to cover your bonsai is just before serious cold weather sets in. If it warms up and snow melts, the bonsai will be self-watering and absorb some water from the ground beneath. 

 In the spring, remove the leaves after the snow has melted. It is not necessary to remove every leaf but do expose the moss-covered  surfaces on each pot. Leaving a heavy leaf cover  too late in the spring  may encourage opportunistic molds to grow on the soil, moss surfaces, or even the trees themselves. 
Some pots  may also  be frozen to the ground and should be left undisturbed until easily loosened to avoid breakage.
Return the trees to your display area in the spring.  Wipe the pots down carefully, remove trash, sticks  and leaves,  and prune the trees  if required.  Let's not forget inspecting the trees for  compacted  root systems,  root trimming,  wiring,  topping up of soil,  design changes or other modifications.

 It's also a great time to photograph your trees while they are bare,  plan their long-term designs,  and transfer them into permanent or  larger pots  as required!