Root death in trees isn't an all at once thing. The finest roots on Jap. maples start to die at temperatures around 25*, or even warmer. Increasingly larger and more lignified roots succumb to chill as the temperature drops, until at (industry accepted standard for Acer p's) around 14*, all roots are killed and the organism succumbs./ It's VERY unlikely you'll be able to protect the plant from killing low temperatures in your vehicle, & insulation only moderates the speed of temperature changes, it doesn't protect from killing highs or lows.

Additionally, if low temperatures don't kill it, soil temperatures above about 45* will stimulate growth. Once the tree has begun growing, it will have lost nearly all it's ability to cope with any freezing temperatures and can be killed by temperatures at or just below the freezing point.

Trying to over-winter in a vehicle is not a viable option. I would ask a friend to allow you to over-winter it in an unheated garage. Set the plant on the floor & cover it with an overturned cardboard box to guard against the night when your friend leaves the door open & it's below 0 outdoors. The overturned box will trap geothermal heat & hopefully prevent the extreme lows that will assuredly kill the tree.

Do remember to toss a little snow on it from time to time so the soil doesn't dry completely. Damp, but not wet is what you're aiming for.

You could also bury the container against the north elevation foundation of a heated building & mulch it heavily. Wrap the top in burlap to help prevent dessication if you employ this strategy.

Al

I have live in NYC and have few maple trees from seeding.

Pots a very small and I don t see how I could maintain a temp above the ones mentioned, would they make it thru winter ?

Is it possible to store then in a fridge ? What do the tree excalty need during winter sleep ? Cold stable temp ? Min humidity ? Changing air ? light ?

Thank you for your help

Ideally, your trees would overwinter at somewhere between 32-40*. Temperate trees require a certain number of 'chill units' to release them from their dormant rest. After this occurs, they pass unnoticed into a period of quiescence (or quiet rest). During this rest, they are fully capable of growing, but are prevented from entering a growth phase by low soil temperatures.

Most temperate trees are stimulated to growth within a few days by soil temperatures over 42*, which is why I suggested the upper limit of 40* .... to be safe.

We don't know what species of maple you're talking about, but even if it's very hardy, it still won't like it's roots being exposed to extreme cold. Roots don't all die at the same temperature, they die incrementally as the temperatures drop. While it varies by species, and genetically by individual plant within that species, all roots on the same plant don't have the same tolerance to cold.

These numbers may not be accurate, but it gives you the feel for what I'm talking about. Most temperate trees, even in zone 4, never see actual 6" soil temperatures much below 27*, with 25* being unusual. This is true, even in bare field agricultural conditions.

We know that the finest hair roots - the ones that do the lions share of the work are the first to die. In many woody plants, these roots begin to die as soil temperatures drop below 28-30*. As temperatures drop further, larger and larger roots succumb to killing low temperatures. The point is - that many trees that SURVIVE are left with only the largest roots to support them because much of the rootage has frozen. These trees are slow to respond in the spring because they need to utilize stored energy to regenerate lost rootage before they can move sufficient water and the nutrients dissolved in water to support either growth or the flush of foliage that makes the food that allows the tree to grow (this, in the case of deciduous material).

So, while trees might survive at extremely low temperatures unprotected, we KNOW it is better for the tree, especially from an energy management perspective, if we give them protection that ensures actual root temperatures don't drop low enough to kill even the finest roots. For most temperate trees, that means we should strive to keep low root temperatures in the upper 20s at their lowest, and below 42* to keep them from growing until spring when we can get them into good light w/o worrying about frost/freeze.

Most of the above was a copy/paste job with a few modifications from a reply I left on this forum about junipers a while back.

They do need some air circulation. They probably wouldn't do well in a frost-free refrigerator unless tented, and they don't need light while dormant or quiescent.

Al