Q. I would like to create some artificial “Growth zones” for some bonsai trees. I would like to create a zone 7. How would I go about doing this and what kinds of artificial lights would I need? Charley Stran – Eau Claire, WI
A. To create a true zone 7 inside a home can be difficult especially if you are growing deciduous bonsai specimens. The USDA zones really only concern themselves with the lowest minimum temperatures. But the zone still has cold temperatures and daylength changes that are necessary in the proper amounts to trigger dormancy and then to break dormancy. You may be able to achieve this in an unheated garage and use a light timer to change the day length to match outdoors resetting it once weekly to follow the seasons. The grow lights could be as simple as fluorescent full spectrum bulbs (or one warm white and one cool white bulb) or as sophisticated as metal halide lamps. If you are using an unheated garage you may need no additional heat but you should be sure that the temperature doesn’t go below 10 degrees F, which is the upper threshold for zone 7. Many bonsai enthusiasts have outdoor hotbeds, which are essentially cold frames with heating cables on the bottom. Most deciduous specimens will need a specific dormancy period where the temperature is between freezing and 45 degrees F. If you can provide that you can grow most deciduous plants. Don’t forget plants have a range of zones that they can grow in. They will have a lower limit zone and an upper limit zone. The lower limit zone is usually based on the coldest temperature it can tolerate. The upper zone has to do with how warm the winters are and dormancy. This is why Florida grows citrus and not peaches or apples. It is to warm in the winter and the peaches and apples don’t break dormancy.