You can keep it outdoors no problem, just be sure to sink it into a larger pot filled with mulch. As long as the smaller pot is in that larger pot it will be protected by the cold.

Don't water at all once the soil is frozen, though adding a handful of snow on top is a good insulator and will water a bit naturally on warmer days. Your porch sounds perfect as a small pot 'just' outside in NY is probably pushing the limits (and cheap pots often crack.. not a good idea!). The mulch is a good one.

I think the previous posters have the mistaken idea that if you insulate the pot, as in using another pot or snow as 'insulation' there is some benefit, but that is not true. Insulation only helps if it helps to trap heat from an extraneous source. For instance, snow on the ground is a good insulator because it traps geothermal heat in the soil and helps prevent it from escaping. Putting a plant in a cardboard box on a deck or deck railing does nothing to prevent the temperature from dropping to whatever the ambient (air) temperature is, though it does slow the process. Using the same cardboard box with the top cut off so the open end is down, and covering a plant on the ground or on a garage floor, provides a MUCH warmer spot for the plant to over-winter. The reason is because the box traps geothermal heat in the same way snow does. Using a question to illustrate: If you put a Dixie cup full of water in a cooler and put the cooler in the freezer at 0*, within a day, the water in the Dixie cup is at 0*. Since it is 'killing low' temperatures that wreak havoc with plant cells, not the simple fact that soil water or inter-cellular water (water between plant cells) freezes, the efforts taken to insulate w/o the insulation trapping heat from another source are ineffectual.

Junipers are hardy, but there is no sense in pushing the limits of what they are able to tolerate. Put your imagination to work and devise a strategy that allows you to keep your plant's soil temperatures above 25* and below 42* all winter. A few days' exposure to temps above 42* can stimulate the plant to growth, considerably reducing it's resistance to cold during the next cold snap, and temperatures lower than around 25* will see some of the more succulent roots succumbing to freeze injury, even though the older and more lignified roots and the organism itself may survive.

If the porch has a south or west exposure, it will almost surely be too warm to over-winter the plant. This, because the plant can't be growing and resistant to hard freezing at the same time. An unheated garage or burying the plant on the north side of a heated building and mulching are both good strategies. If you adopt one of these strategies, do make sure the plant gets some moisture and doesn't dry entirely, though you don't want the soil to be wet. Another concern about using snow for 'insulation' is, snow melts, and if you're regularly piling snow on a pot all winter, there is considerable risk that the plant may be too wet for extended periods.

Good luck!

Al

Sorry Al, but I am going to have to disagree with you. Mulch is a great insulator for outdoor bonsai. That is what I was always taught to use to winterize my trees, and it has always worked. I did not say to simply use another pot or to use snow, but to use another pot that is filled with mulch. This way the roots are protected from the freezing winds.

Thank you all for the input. My next question is whether or not the bonsai requires sunlight during the winter season? It seems like in a garage or under a box or on the north side of the house there would be virtually no exposure to sunlight. How would wrapping the pot in a burlap bag and then put into a larger pot filled with mulch work? Regardless of whether I put it on the porch or in the garage it will be exposed to very cold (single digit temperatures) for extended periods and I don't want the roots to be affected by that. Putting the plant outside is not really an option as the ground is frozen and digging would be very difficult.

Ry - Mulch is a fair insulator if your plants, or plants and pots are sunk into the ground and then mulched, which actually makes the second pot entirely superfluous; but what you suggested: ".... sink it into a larger pot filled with mulch. As long as the smaller pot is in that larger pot it will be protected by [from] the cold." is not true. If it WAS true, all we would need do to keep the Dixie cup I mentioned in the example above would be to mulch it and put it in the freezer. It just doesn't work that way. Even in the example above, where I offered the illustration of the Dixie cup in the cooler in the freezer, the water in the cup would quickly freeze; however, if you had a warm curling iron or other source of heat inside the cooler in the freezer to capture (that extraneous source of heat I mentioned - most often geothermal heat) heat, the water would not freeze.

Wind has nothing to do with killing low temperatures. Windchill has no effect on plants. Wind might desiccate exposed tissues, but wind doesn't make the soil or air any colder unless we can add in the effects of evaporative cooling, and since we are talking about temperatures below freezing, evaporation is a non-issue. Even sublimation, which is when a solid like ice or snow changes directly into a gas, skipping the liquid phase entirely, doesn't enter the picture here.

Ra - Dormant plants don't need light. Technically, when temperatures are high enough, evergreens are capable of carrying on a tiny little bit of photosynthesis in the presence of light, but it's so insignificant we usually simply answer no.

I wasn't suggesting you cover your plant with a box outdoors, only using that as an illustration and a viable method of 'pushing the zone' when you over-winter plant material in the garage. I over-winter at least 50 junipers in my garage with no protection. About 4 times each winter, I toss a little snow on them so they don't dry out & call it good.

You needn't fear having the soil freeze. Here is a copy/paste job from something I wrote on another thread. It explains a little about cold-hardiness:

"Your question more closely asks what temperatures will my tree tolerate, but it leaves unanswered the question of what temps are best. It would be best if you could keep actual soil temperatures above 25 and below 42* for the winter. Here is a longer explanation about cold-hardiness I left on this forum previously. If it leaves you with questions, just ask:

Commonly, each species of plant has a general range of cold-hardiness. Within species and cultivar, cold-hardiness is genetically determined. That is to say that a plant that is propagated from cuttings or tissue culture will have the same ability to resist cold as the parent plant. Plants cannot "develop" a greater degree of cold-hardiness by repeated or prolonged exposure to cold, even after 100 years (trees).

If we pick any plant at random, it may or may not be able to withstand freezing temperatures. The determining factor is the plants ability to prevent freezing of bound water. Bound water is the water inside of cells.

There are actually three kinds of water to consider when we discuss "freezing". The water held in soil - When this water freezes, and it can freeze the soil mass solid, it doesn't necessarily kill the plant or tissues. Then there is free or unbound water, also called inter-cellular water. This is water that is found in plant tissues, but is outside of living cells cells. This water can also freeze solid and not kill the plant. The final type of water is bound water or intra-cellular water. If temperatures drop low enough to freeze this water, the cell/tissue/plant dies. This is the freeze damage that kills plants.

Fortunately, nature has an antifreeze. Even though temperatures drop well below freezing, all plants don't die. In hardy plants, physiological changes occur as temperatures drop. The plant moves solutes (sugars, salts, starches) into cells and moves water out of cells to inter-cellular spaces in tissues. These solutes act as antifreeze, allowing water in cells to remain liquid to sometimes extremely low temperatures. The above is a description of super-cooling in plants. Some plants even take advantage of another process to withstand very low temps called intra-cellular dehydration.

The roots of your trees can stay frozen for extended periods or go through multiple freeze/thaw cycles w/o damage, so long as the temperature does not fall below that required to freeze intra-cellular water. If roots remain frozen, but temperatures remain above killing lows, dessication is the primary concern. If the tree is able to take up water, but temperatures are too low for the tree to grow and make food, stored energy becomes the critical issue. Dormant and quiescent trees are still using energy from their reserves (like a drain on a battery). If those reserves are depleted before the tree can produce photosynthesizing mass, the organism dies.

There are a number of factors that have some affect on the cold-hardiness of individual plants, some of which are length of exposure to seasonal cold, water availability (drought stressed plants are more cold tolerant), how recently planted/repotted, etc

No one can give a definitive answer that even comes close to accurately assessing the temperature at which bound water will freeze that covers the whole species. Unbound water is of little concern & will usually freeze somewhere around 28*.
Some material will be able to withstand little cold & roots could freeze/die at (actual) root temperatures as warm as 25-27*. Other plants may tolerate much colder actual root temperatures - as low as 10*. There's just no way of knowing unless you have a feeling for how cold-tolerant the genetic material the plant was derived from might be, and finding out is expensive (from the plant's perspective). ;o) Another example of this genetic variance is that trees found growing and fruiting well closer to the equator need no chill time, while other trees, derived of genetic stock from a more northerly provenance may need a period of chill to grow with optimum vitality in the subsequent growth period/cycle.

It's wise to remember that root death isn't instantaneous at one particular temperature. Roots succumb to cold over a range of chill with cultural conditions affecting the process. The finest roots will die first, and the slightly thicker and more lignified roots will follow, with the last of the roots to succumb being the more perennial and thickest roots.

Since any root death is a setback from an energy allocation perspective, and root regeneration takes valuable time, it's probably best to keep actual root temperatures in the 25-40* range as long as we can when the tree is resting, even though the organism as a whole could tolerate much lower temperatures. Even well established trees become very much like cuttings if all but the roots essential to keep the tree viable are lost to cold. Regeneration of roots is an expensive energy outlay and causes the trees to leaf out later than they normally would and shortens the natural growth period and reduces the potential increase in biomass for the next growth cycle and perhaps beyond.

and

We know that when trees are exposed to freezing, 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 30-32*. 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 exposure to borderline killing 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.

Hope that helped.

Al

It will certainly need light from sometime in Feb. onward, but for the next month or so, probably not more than a minimum, if that.

The importance of light as it relates to spring growth and even the onset of spring growth is a very insignificant consideration until temperatures rise above and stay above 42-45*.

Al

When; I lived in western Pa, I found out (when I only had a few trees) that they overwintered well under a large evergreen shrub next to the house -- set in a bed of mulch with a little covering the pot. It was simple and worked very well.

As I accumulated more trees I wound up building a 'cold house'. The frame came from an old greenhouse (smaller one) covered with opaque plastic. After the first few hard frosts the trees went in there and it was sealed up tight, as tight as I could make it. The result was a 'climate' of ambient temp and a decent amount of humidity with no wind. If it did become too dry I simply opened the door and shoveled snow in.

They stayed in there until the weather began to moderate into the high 30's then it would slowly be opened up more and more as temps allowed.

I also had much larger and well established trees spend winters on the bench with no protection at all. Yes, they developed slower in the spring because of some fine root loss but never lost one.

Bob

Thank you all for your input - it has been very helpful. Al, your comments have been very thorough and explanatory and I truly appreciate the time you took to provide such input! Have a happy new year!

Rachel

You're very welcome. Thank you for taking the time to say thanks, and to just say 'hey'. ;o)

You too, Rachel - Happy New Year.

{{gwi:5839}}

Be always at war with your vices, at peace with your neighbors, and let each new year find you a better man. ~Benjamin Franklin

{{gwi:3287}}

Al

Great Post!

"As I accumulated more trees I wound up building a 'cold house'. The frame came from an old greenhouse (smaller one) covered with opaque plastic. After the first few hard frosts the trees went in there and it was sealed up tight, as tight as I could make it. The result was a 'climate' of ambient temp and a decent amount of humidity with no wind. If it did become too dry I simply opened the door and shoveled snow in. "
I read an article in the American Coifer Soc Qtry mag, the writer placed container conifers in white plastic bags in an attempt to help the plants winter. I am guessing - Somewhat similar to the white covering in this unheated hoop house. I assume that the unheated hoop house has lots of pots and maybe this would impact the retending of some heat and it is not on the same scale as a pot in a white plastic bag, but it ther a possiblity that there might be some benifit from the bag?

Also I was not aware that conifer could go in garage in winter - as long as you remove as the temps rise -- thanks
Mike

I have many friends that have pits dug about 4-5 ft deep and lined with treated lumber. Good drainage is essential, as you can't afford to have the pit fill with water when it rains or during periods of rapid snowmelt. The trees are nestled in the pits and the pit covered loosely to allow plenty of air circulation. They get snowed on through the spaces in the covering, so watering is rarely a concern. Geothermal heat from below the frost line keeps the trees warm enough that trees up to 2 zones warmer do fine; but still, trees remain cold enough they remain dormant until it's appropriate to remove them from their cave in the spring.

Al