Its starting to get a little cold here in Birmingham so I have started to look at winterizing my bonsai. So fortuitously I am writing an article on it! ;) If you live in a tropical zone, protecting your bonsai trees when the temperature begins to dip near 40 F degrees can be as simple as bringing them into a more protected and warmer inside environment, and making sure the humidity stays up. However, if you live in a temperate zone where winters can hit and stay at or below freezing, like it does here,  you need to devise a method of allowing your bonsai their natural dormancy and protect them from freezing.

Methods:

  • Mulch – Use a mulch that covers the lower first or second branches of your tree.  In addition, placing your bonsai under any structure that protects it from heavy icing and dry winds but allows moisture is also recommended. If you must water, do it earlier in the day and only when temperatures warm to 45-50 degrees.  Rule of thumb is: if the rootball is solid, don’t water – if it’s loose, water sparingly.
  • Unheated greenhouse (or the equivalent) – Make certain that if there’s the possibility that the temperature can hit below freezing, use a small heater to sustain a moderately cool but not freezing temperature.  If you opt for this method, don’t bring you bonsai in and then put them outside again on a warmer day.  Consistency is important during dormancy.
  • Cold Frame – Make a cold frame, outside, that’s raised, allows for light (but, not direct sun) and which can be opened, from time to time, to aerate your dormant bonsai.

Timing

Whatever method you choose, putting your bonsai into protection before the first freeze is your first best step to successful wintering over.  Conversing, taking your tree out of protection too soon in the Spring can have the same affect.  Wait a bit longer to make certain all chance of freezing and frost have past before introducing your bonsai back to a shaded, outside spot. For my purposes I am doing 2 of these. I am putting most of my trees outside in a mulch bed but a few more tender ones are going to stay in the basement. I plan on posting pictures of my setup once I get home and have time.