How do I prepare my outdoor bonsai for winter?
> Obviously you do not have to worry about winter care of bonsai if you live in the tropics. This discussion is for care of temperate trees where winters are harsh.
> The concept of wintering over a bonsai is not too much different from wintering over what is already planted in your yard. It is not necessary to be unduly frightened about the onset of winter and bonsai care. Most temperate climate trees grown as bonsai are capable of handling the severe weather as long as a few simple conditions are met.
> Winter winds combined with temperatures below the mid twenties Fahrenheit (or below -5 Celsius) will freeze dry almost any bonsai. This is the biggest enemy.
> Attempting to keep temperate plants warm by placing them in the sun is a mistake. The added warmth from exposure to too much direct sun can cause a tree to wake up from dormancy too early. If this is followed by temperatures once again plunging down very low, the water in the sap can freeze within the cambium layer and kill the tree.
> It is usually not necessary to take trees out of their pots. Good pots are capable of handling the temperature changes. One exception would be Trident Maple. This particular tree should be removed from its pot and the soil ball buried in the ground or a large box. If it is wintered in the pot the roots will turn to mush.
> All other temperate plants can be kept in a sheltered area out of direct sun and wind. The pots should be mulched or buried to the top of the rim in the earth. Burlap barriers work well as a wind break. You can also make a wall using bales of straw.
> If there is not much snow or the weather warms it is possible you will have to water your trees from time to time. Rule of Thumb: If the soil ball is frozen, you do not need to water. If the soil ball thaws and starts to dry you must water.