canada here has the lowest Temp in winter about -10C (15F)

but an expert i know told me that it should be fine even if the temp goes extreme cold if juniper is placed in a closed box or somehitng

i have three questions...

1) during the extreme cold temp, is it OK for juniper to get NO sunlight?(for about 2-3weeks i think)...iam thinking about putting him inside a box and place the box outside

3) do i water it during the dormancy? do i water it during the extreme cold period?(-10C , 15F)

2) if i water it during that time, the water is going to freeze...so the soil is going to get frozen too,,,is it safe for juniper's root?

please help me~~~~~~

2) yes, never let the soil go completely dry; neither, do you want it to be excessively wet.

3) Frozen roots do not necessarily mean a dead plant, or even an injured plant.
Commonly, each species of plant has a general range of cold-hardiness, but 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 cell walls.
There are actually three kinds of water to consider when we discuss "freezing" or cold-hardiness. 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 bound water, the frozen cells and the tissues they form die. 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.

Any/all parts of your plants 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 plants are still using energy from their reserves (like a drain on a battery). If those reserves are depleted before the plant can produce photosynthesizing mass, the organism dies.

There are a number of cultural factors that also 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.

I bet that was more than you bargained for, but I copy/pasted most of it from a reply I'd left somewhere previously.

Al

Josh