Wintering Bonsai followup

Okay, this seems to be the best possible solution I have come across to keeping bonsai in zone 4b at -30 to -20 F lows outside (southern Minnesota). Constructing a 3-3 1/2 foot trench below the surface with a glass/polyethylene cover and maybe supplemental artificial lighting. The frost line is about 3 feet below the surface, so I would imagine this would raise the temperature of the trees considerably if they were to be placed directly in the soil. 3 and 1/2 feet is steep for sure, but there are many places a trench could be dug in the yard so avoiding underground pipes would probably not be a problem.
If there is anyone who has a better suggestions or a reason why this would not work (especially by someone who has grown bonsai in cold climates), please say so. Thank you!
~Michael
PS the next best thing seems to be to keep them in my unheated garage, where temps I don't think get below -10 or -15, and insulate the plants further and provide them with a heating pad.

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Tony

I'm in zone 7 so I don't have to deal with any temps as cold as yours. Much depends on what kind of trees you are trying to grow. The trench idea can work but I don't think you'll need to go that deep. Any trees that are hardy to your area can take a good deal of freezing so getting below the frost line isn't necessary for those.

You don't want to put them in a hole and cover *the top completely though, they'll still need some air circulation. Just make sure they are protected from strong sustained winds that can dry small branches. When the trees are dormant they stop growing and don't need light so there's no need for artificial lighting. *One important caution: You want to place blocks or something at the bottom of the trench and set your pots on those. When the spring thaw comes the trenches can hold water and you don't want your bonsai setting in a mud puddle, that could rot the roots in a hurry.

Tony

Thank you for the informative response. Apparently most plants don't need any light whatsoever when they're dormant..? I've heard some say while it's not neccessary it is beneficial for the plants to get some light. Does this vary from species to species?
Thanks,
~Michael
PS. To those knowledgable, I know they supposably are difficult subjects but I've heard Chinese Wisterias are hardy to zone 3, while others say only to 5 (and admittedly I haven't seen any in the area). Any experience with these especially as bonsai?

Tony

Mike, there hasn't been alot of research [to my knowledge] into the subject of dormancy and light levels and particular temperatures needed to sustain dormancy.I have derived what I know about it mainly from common sense and observaition.

Firstly, it's not the cold temps that triggers the start of dormancy in plants, it's the shorter days and low light levels of autumn. This triggers hormones in the tree and tells it to start storing reserves of sugars and nutrients in the roots and to curtail the movement of sap to the top of the tree. At the same time the temps are getting colder and keeping the tree from putting out new buds.

Second: We need to separate temperate deciduous and temperate evergreens here. Deciduous trees lose their leaves every winter so it's apparent that they need no light. *The controversy usually comes when discussing evergreens. Here's where common sense and observation come in. I've never seen any tree put out new growth with sustained temps below 40 degrees, and no one will convince me that the trees need light when when they're below 32 and the rootballs are frozen solid. Trees need light for chlorophyll production and photosynthesis to produce more sap, to produce new growth, so why would the need light when they are dormant? It's just not going to happen at those temperatures. You can see this process at work when junipers go dormant. The chlorophyll will leave and the foliage will change color. What you see is the true color of the foliage, some bronze, some golden, some red, some purple, depending on the species. This is not to say that the sap flow stops altogether. The tree is still sending some sap to the top to replenish the moisture lost to transpiration, but it doesn't need light to do that.I think the dissagrement comes from spring and fall when you can get a stretch of unseasonably warm weather. Evergreens are usually the last to go to sleep and the first to wake up so you don't want to put them into winter storage too early or take them out too late. At these times of warm temps they will need light.

To sum up: Low light and shorter day triggers the start of dormancy and the cold temperatures keep the tree dormant. The warmth of spring triggers the tree to come out of dormancy and start pushing new buds. And no, trees don't need light when they are truly dormant. At least this is how I've got it figured out in my pea pickin brain.

Tony

minotaur77

I have a problem along the same lines as this thread. I was lucky enough to find a company offering young wisteria (1 to 2 years old) for a reasonable price. I purchased 6 of them in October.

They arrived dried out, but their root structure was in good shape. I promptly planted them under my indoor grow lights and was able to get one to throw out one group of three shoots. These slowly lost their color and dried out. Now all I have 6 wisteria trunks.

I am guessing that these plants have gone dormant. They have strong trunks and the root structures seem to be holding up (they aren't rotting out at least). From reading the previous reply, I can assume that by warming these plants up, I can wake them up from the dormant period. Does anyone think this will work or have experience in this area? Right now their temperature under the light is about 60 degrees farenheit. I am having the same issue with a trumpet vine.