Overwintering Hardy Bonsai
From BonsaiWIKI
Over Wintering Hardy but “Touchy� Bonsai In Zone 5 Northeast Ohio
by Dale Colchoy http://www.WildThingsBonsai.Com
Over the past 26 years I have found that some of my “Hardy� bonsai are very touchy to winter cold in my Zone 5 area. We commonly get zero degrees Fahrenheit weather in the winter for several days and I can remember it as cold as –25 here at my garden. Over the years I routinely had trouble over wintering such trees as
- Trident Maple
- Bald Cypress
- imported Satsuki azalea
- imported Needle Juniper
and a few other trees I have experimented with. By “trouble� I mean total loss of the tree or portions of the tree including fine twigging and/or major sections of larger limbs or tops. I should mention that my trees are placed into my UNHEATED fiberglass 16’X24’ greenhouse around the third week of November each year ( depending on how the weather has been or is looking). This greenhouse keeps the trees at very near the outside temperature throughout most of the winter with only about 5 degrees warmer inside. The greenhouse is unheated except for a small 1,500 Watt electric heater which I use in early Spring on nights when we are expecting a heavy frost after some of my trees have begun to leaf out in the greenhouse, but before I wish to move them out to their benches.
Several years ago I began a new system that has all but stopped the various overwintering problems in all but a few very nasty winters. The problem trees are placed in boxes for the winter and back-filled to over the pot with mulch. I use several types of boxes. I use inexpensive Styrofoam “coolers�, Styrofoam boxes that tropical fish are shipped in, or Styrofoam boxes that fruit is shipped in, or Styrofoam boxes from the hospital/Doctors offices for transporting organs/drugs that need to be kept cold, or large plastic “surgery kit� boxes from the hospital that are used in surgical procedures and then discarded. Depending on your personal “connections� I’m sure you can come up with some storage boxes.
I commonly drill some one-inch holes in the bottom of the boxes. Then I place 2-3� of mulch in the bottom. After placing the potted tree on top of the mulch I then pack mulch around the pot and up over the pot rim a few inches. These boxes need an occasional watering but stay nicely moist most of the winter. Just be sure to not over water! For one extremely large Bald Cypress in a large, but shallow, fiberglass box I also wrap a fiberglass insulation “bat� around the box and then back-fill behind it until I’m over the pot depth. You can also use these mulch boxes to “snug-in� a few small potted trees or plants around the larger trees. It seems these boxes are usually the last items I get to each Spring when moving trees out to the garden and they are always doing nicely in the boxes. After unpacking these boxed trees I simply spread the used mulch into my existing landscaping mulch and buy new bags for overwintering every fall.
A second method of overwintering touchy SMALLER trees is to build a Styrofoam lined box in a protected area. I have a box about 2 1/2ft. X 6 ft. that sits up against a shed on the East side (no wind). It is of treated wood construction with a 1� Styrofoam insulation liner on the inside. It is bottomless and extends about 6� into the soil. The bottom is filled with gravel for drainage. The top is clear Plexiglas and hinged to prop open when needed. I can get about 30 shohin bonsai in this box and I have never lost a tree in this box.
Dale Cochoy Wild Things Bonsai Studio Hartville, Ohio
