I have started several tree's from seed (Acer varieties) and its time to put them into dormancy, but I am not sure the best way. I live in North Dakota, Zone 3, and we always achieve -30 at least once, and a 2 week snap of -20 which will kill most potted plants. Just leaving them outside dormant will not do it, and they will come out of dormancy too early if this is done because temperatures above root zone always warm faster than the ground.

What should I do, should I apply the Minnesota Tip, and bury the dormant stock in the ground. Place it in a bag full of leaves and wet the leaves down, or simply bury the potted plant in snow. Is it ok to take a plant that is totally dormant, clean the roots out and put it in the refridgerator until ready to take out of dormancy like "Bare Root Stock" from a nursury?

You could always put it in a garage for a time, ideally next to a window. Garages are usually 10 to 20 degrees warmer than outside temperatures.

Thank you for your prompt response, I appreciate the opportunity to have discussion on this. I really don't want to do a Minnesota Tip on them.

I have tried storing in a garage with regular potted stock, and the only varieties that survive are Salix (willow). A local nursury winters their potted stock over by burying them in leaves and cover with plastic.

Its under my understanding hardiness is actually a root zone thing, and the only apple tree's we can grow in the ground are grafted onto a single very old crabapple stock. I am new to the bonsai venture, but I would think a small pot exposed to temperatures under 0 would kill the tree's because the mature trees roots extend far below the frost zone (4'-6' deep). Most unheated garages easily fall to -20 on occasion in this area and would freeze the entire root ball solid.

We have a problem with acers called Sunscald, where in the spring they warm too soon, and the sap starts running when the sun shines on them... then it freezes at night causing the sap to freeze and rupture the cambium... typically on the south side of the trunk. Although I think this is a scarring I will try to emulate, I don't think putting them in a window in cool temps would do well.

Keep them in the garage and put heating pads under the pot with a thermostat set at maybe 30 deg F.

once the roots are frozen there is no reason to worry. put it somewere out of the wind (wind kills not temperature) and out of sun. the trees are dormant there is no need for sunshine or water (pines need light and water over winter) . the best thing to do is burry them in snow . my trees stay frozen well into april some years