Tip of the Week  #19

In the previous two articles, we've covered wintering bonsai in an unheated garage, tool shed, or a cold frame. Jon from Carroll, Iowa asked if there was a way to winter temperate bonsai indoors, and the answer is "Yes." Starting from the easiest method, if you have an unheated room with at least one window, that's the place. The next best spot is a window with a space between the outer (storm window) and inner window that's wider than your bonsai. If you're fortunate enough to have that kind of place available, just put your bonsai between the windows and close both. If it gets too cold between the windows, you can "crack" the inner window a little. This will take the edge off the cold where the bonsai is without overly cooling the room. It is important to remember to water as needed.

"As needed" is a very variable term, so let's discuss it in regard to any and all wintering methods discussed here. In summer, watering is easy. Every day or two, just water. No problem. In winter, your bonsai may still need water every couple of days, or at the other end of the spectrum, it may be able to go without water for weeks at a time if the soil is frozen 24 hours a day. The important thing to remember is that without sufficient watering, your bonsai will die.

In winter, it is imperative that you check you bonsai often to determine when it needs watering. It is also important to determine if the soil is dry or frozen. Frozen soil feels like soil that hasn't been watered in a month, but it actually may be moist. When soil is frozen, water will not soak into it. The best way to know the difference is to place a Minimum/Maximum Thermometer (available in the "Supplies" section of our "Product Catalog") next to the bonsai. It will tell you the current temperature as well as the highest and lowest it's been since you last reset it. If you don't have one handy, and don't want to spend any money on one, there's a simple option available. Just place a Snapple Cap (or anything similar) next to your bonsai. Fill it with water, and if it's frozen, there's a pretty good chance that the soil is also.

If none of the above wintering options are available to you, you can make a very good indoor wintering area without too much cost or effort. First, choose a window. The further away from a heat source, the better. Measure the space on the inside, between the left and right sides of the window frame. Cut a piece of one inch pine board (wide enough to fit your bonsai), and secure it to the window sill with screws, brackets, or any other method you see fit. Attach upright pieces to the two corners of the shelf that extend into the room. They can be wood, or any other material that you choose. They should be at least 4 inches higher than your tallest bonsai.

Finally, cut a plastic sheet (the kind that's sold to weatherproof windows works well) to go from the window frame, around the two "uprights", and to the frame on the other side. Masking tape is the best bet to attach the plastic. It holds well, and is least likely to damage the finish when you remove it in spring. Tape the plastic to the shelf, and you're done. The principle that makes this work so well is that cold air falls, and warm air rises. The cold air from the window will "cascade" into the box you've created. As the warmth from the room heats the air near the three sides inside the room, the warmed air will rise an be replaced by the cooler air settling in from the window. It not only keeps your bonsai cool, but the air circulation will discourage mold and fungus from growing on your moss. For something so simple, it's surprisingly effective.

A Humidi-Grow Tray (Supplies Section of the Product Catalog) is ideal for this type of wintering, because it not only adds humidity to the air, it also gives you a way to water most bonsai without removing them from their cold environment, and the water is the same temperature as the soil.

When choosing a location, if more than one option is available, take the one with the least amount of direct sun.  In summer, sunlight is necessary for growth.  In winter, a little light is good, but the less sun the better.  Watch for signs of new growth as spring approaches.  As it begins to appear, more direct sun will be necessary.