Question
QUESTION: I live in Colorado Springs the temp gets around -20 or more in winter- the lilac is good to -40. I have a royalty lilac, delphinium and spruce in large pots-I have very little space and physically cannot lift pots- how and with what do I wrap them to try to avoid freezing them to death?  Thanks so much

ANSWER: The thing to understand about soil in containers in winter, is that it is usually around a zone colder then the ground. The plants are dormant above the soil, but the roots are still actively using water and nutrients. Not as much as when the plant is growing, but if the soil is frozen for a long time, then they are not able to keep the plant alive. So, it is very important to prevent the soil in your containers from freezing. Wrapping the container with insulation and plastic can be helpful. Putting a thick layer of mulch on top of the soil will help. Moving the container to a protected area will help. A covered patio next to the house that is out of the wind, and frost, would help.

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QUESTION: Thank u for your response - I am a REAL NOVICE - so would you explain what to use as insulation - what are you referring to - bubble wrap or would just a plastic sheet like a drop cloth type of material work?  Thanks again.

Answer
I was referring to "house" insulation. For best protection, two layers, covering the container completely.
Then put plastic over it to keep it dry.
Plastic alone is not thick enough. You want something that is thick enough to keep the temperature stable.
If you have a probe thermometer, use it on the coldest nights, to test the soil to see if it is freezing. If it is, then you will need to put on more insulation. At -20 even the insulation without any other protection, may not be enough to keep the soil from freezing.

(If it were me, I would get a strong friend, with a hand truck, to help you move the pots into a dry shelter. A garage, shed, or basement will work well.)