Unlike their ground grown equivalents, Bonsai don't thrive outdoors in our Canadian Winters. Some very mature conifers could survive, depending on exact location, sheltering from wind, age and size of pot. But let's just stick to no Bonsai should be outside during Canadian winters, just to be on the safe side.
One of the most important factors in growing a Bonsai is understanding what type of tree you have and trying to imitate it's natural climate and seasonal rhythms.
Ficus, Star of David, Black Olive, Jade and others, grow in tropical conditions. Meaning to maintain their natural rhythms they must be placed in a warm area with plenty of sunlight. The most common issues when keeping these Bonsai indoors occur when there is not enough humidity or air circulation. Be sure to place your tropical Bonsai in an area that receives at least half day sun and is warm (above 18° Celsius). It's important to mist your Bonsai at least every other day and all tropical Bonsai can also benefit immensely from a humidity tray placed under the pot. Make sure the bottom of the pot does not touch the water level in the humidity tray. Cracking open a window on warmer days by the Bonsai can help circulate the air, improving cell regrowth. These Bonsai can also do well as indoor Bonsai year round. If growing your tropical Bonsai outdoors during the spring, summer and fall, make sure to bring the Bonsai indoors when temperatures consistently fall below 10°.
Sub Tropical Bonsai:
Chinese Elm, Fukien Tea, Buddhist Pine, Bougainvillea and others grow iin sub tropical conditions. For the most part they can be cared for like tropical Bonsai. The main difference being that they can stay outside until temperatures start falling below freezing.
Deciduous & Coniferous Bonsai:
Maples, Oak, Pine, Cedar and others grow in colder climates. These trees thrive outdoors and should be kept outside as much as possible during the spring, summer and fall months. However, during the winter the fact they are in pots, exposes their roots to extreme conditions, so indoors they must go. In nature these trees go dormant in the winter months, saving their energy and almost completely stopping growth. In order to maintain the seasonal rhythm of these Bonsai, they must be brought in to an unheated area such as a garage, cold room or three season room. There are ways that they can be kept outside, but it is not recommended, so we won't touch upon those.
In an ideal world, the best way to store your bonsai over the winter months would be, in a cooler or other well insulated container. Without closing it and covering it up until it's first branches in mulch.
It's important to not fertilize deciduous or coniferous Bonsai during the winter or even late in the fall, letting the tree slow down it's growth. Don't forget to check on your Bonsai during the winter, although it will not require much watering, you do need to keep the soil moist. Maintaining the same level of dryness or moisture depending on the advised watering schedule for your specific tree.