I am considering to plant my Emerald Cedar in the bottomless pot (I will cut the bottom of the pots out) which means the pot will be there permanently since the roots will grown into the soil. I need your advice for how do I insulate the pot for winter since it will stay outdoors. (my pots are weather resistant).
Thank you very much.
Thank you for contacting the Toronto Master Gardeners with your question about how to provide winter insulation for a bottomless pot that will be planted with your Emerald Cedar. Presumably the root ball of your Emerald Cedar will be initially planted inside your bottomless pot, and over time the roots should grow down and become well established in the ground below. Once established in the ground, your plant will not benefit from any above ground insulation, but prior to that, some insulation might help to protect the developing roots. I think you are also asking about insulation to protect the pot itself.
In order to insulate the roots of your plant, the pot should be large, the bigger the better. The greater volume of soil will help to insulate the developing roots. Since Emerald cedar is not a fast growing plant, for the first winter or two (or until it is firmly anchored in the ground) I suggest building a fence out of chicken wire around your pot, and filling the space between the chicken wire and the pot with hay or straw or mulch, up to the level of the top of your pot. Cover the surface of the soil in the pot as well. This should be done prior to the first hard frost in the fall, and removed in the spring when there is no longer any risk of a hard frost. This insulation will also provide protection for the pot itself during the winter freeze / thaw cycles.
Once your Emerald Cedar is fully established in the ground, the only need for any insulation might be for your pot (the container, not the contents). Since your pot is weather resistant, I am assuming that it will need minimal winter protection, so I suggest wrapping it in thick burlap during that time.
The following links might be helpful as you consider the various materials that pots are made of and how to insulate them. The first one includes comments about the use of Styrofoam for insulation (not recommended).
Insulating Pots : Is It Worthwhile ?
How to Protect Pots and Planters From Winter Damage
The Cold, Hard Facts on Protecting Potted Plants
All the best with your plant and its bottomless pot !