Getting Ready for Winter: November and December

Anne Spencer

Complete dormancy is built into the life process of plants native to cold weather areas. Dormancy: All growth above ground is suspended. Buds previously formed remain closed. Respiration is at low ebb, comparable to hibernation in animals. The process enables trees to survive.

The signal to prepare for dormancy is not so much the drop in temperatures but day length. As days become shorter, the glucose produced in the tree by photosynthesis is distributed throughout all parts of the tree to be assimilated and stored as a reserve of energy for the winter months.

The bark thickens as the cambium cells build a new layer of inner bark. As temperatures drop, the tree covers all its buds and needles that will remain during the winter with layers of a waxy secretion. Before winter arrives, the tree has completely sealed and insulated its exterior (above ground) from the cold.

Roots confined to a container can't survive the same low temperatures as the above ground parts. This is why we have to take special precautions for our winters.

Care preceding dormancy:
-Stop fertilizing deciduous plants in late summer except for 0-10-10 (to October). Conifers and evergreens can receive a low strength timed-release fertilizer all winter as their roots are active during the dormancy period.
-Postpone all but emergency pruning until late winter/early spring.
-Reduce watering, especially if the plants are in poorly draining bonsai pots.
-Keep all but tropical and non-hardy plants outdoors to allow them to prepare for dormancy.
-As the plants lose their leaves, keep the pots and plant area cleaned up.

Care just before winter storage:
-Look for insects, etc.
-Remove moss from trunk and root area.
-Now is a good time to photograph your prebonsai and bonsai. Record keeping is important.
-Dormant spray if needed. (check temperature and species restrictions on bottle)
-Potbound trees fare less well in winter. They need more protection. One could temporarily repot them into larger containers.
-Remove all forgotten/missed/too tight wire.
-If deciduous trees still have leaves when you're ready to put them into the storage area (as late as the second week in December for me), remove them by hand. This will force them into dormancy.
-When night temperatures are dropping below freezing on a regular basis, move plants to winter quarters. I move my plants into storage between November 17th and December 15th, depending on the harshness of the weather.

In Winter Quarters:

-No direct sun (equals fluctuating temperatures): Warmth causes plant's cells to fill with water. Then, with a quick drop in temperature to below 32 degrees the water freezes and cells rupture. To avoid this, Nature increases the permeability of the cell's walls as temperatures drop, thus enabling water to leave the cells if the temperature changes are gradual.
-Moisture: If under a covered area you will need to check each at least weekly for dryness. Water to keep them not too wet or too dry. Pots break if a frozen root system is real wet, and plants die if the roots are too dry. Watering in the morning is best.
-Fresh air: Good air circulation prevents mold and other problems.
-Leaving moss on causes watering problems.
-Accessibility: You should be able to reach all your plants. Also they need to be where you won't forget them.
-Light: This is related directly to the extent of the dormancy. Totally dormant deciduous trees don't need any light at all. Conifers do.
-Good drainage in the area, and in the pots.
-Protect from rodents, cats, etc.
-Provide mulch (not peat moss as it holds too much water): Bury the pots up to their rims in bark dust.

Possible Winter Quarters:
-Cold frame
-Greenhouse (cold, or heated to just at 32 degrees)
-Under patio roof
-Under snow
-Window well
-Unheated basement
-Unheated garage
-Under a large tree. Make sure it won't fall over during the winter! (this happened to one of our members a few years ago)
-If you only have a few plants you can put them in a box, surrounded by bark dust, covered with another box.

Take into consideration where you are. If you live in a protected area, using a garage or basement might be too warm. Your trees would come out of dormancy. If you live up the gorge and have lots of wind, a garage might be necessary.

What I do:
I live in a protected (from all but the heaviest gorge winds) area north of Beaverton on a south facing hill. Most of my trees in bonsai pots, along with less hardy trees, and trees with poorly developed roots, are kept under a patio roof. There is 8" or more of bark mulch on the concrete for insulation and protection. The area is surrounded on all four sides by outdoor pegboard, house wall, and fence. The wind is blocked but the air circulates, and there is no sun. I can reach it with the hose to water.

My conifers and hardy plants in training pots are sitting on the ground under the bonsai benches. They are nestled into deep bark mulch, and the pots have been removed, for good drainage.

In the past I have removed the pots from my smallest bonsai (mame, shohin, and chuhin) and just planted them in a well drained, protected, and mulched area in the garden. This works quite well, especially since they are usually repotted every year. Remove them from their pots carefully.

Winter is a good time to gather all the materials you will need in the spring repotting rush. And update your plant records/inventory, and pictures. With yearly pictures you can really see the changes that are happening so slowly through the year.

I hope this article is helpful in stimulating thought and discussion among the club members. Keep in mind there is never one best way to do things when growing bonsai.