I live in Northwest Montana, growing zone 5, and last year I planted a number of different perennials in my backyard. Some grasses, and some flowering and woody shrubs. Some of the plants were planted in the ground, while others were planted in medium to large plastic pots. It gets fairly cold here and will sometimes stay below 30 degrees for many weeks during the dark winter months. A foot of snow is typically on the ground from early December through the end of March.
Spring has now sprung, meaning temps are in the high 40s and low 50s most days, down to the high 30s at night, and everything is starting to come back. The days are getting longer too. I’ve noticed that all of the perennials I planted in the ground are coming back as expected, but almost all of the potted plants don’t appear to be growing at all. They look as dead as they looked in January. Is this because the pots got so cold it actually killed the roots, compared to the ones buried in the ground?
If that’s the case, what should I do with the potted plants next year? Put them in my garage where the temperature stays above freezing all winter? I bought perennials because I didn’t have to have to replant the pots every year.
They might come back, but more than likely they froze.
You can put them in the garage or unheated basement, but you might have better results by “heeling in”, that is partially burying them and covering with mulch.
If you have a sheltered corner to do it in, so much the better.
Plants in pots are not only subjected to more severe winter cold than their counterparts in-ground where the roots are better insulated, but also have to deal with greater temperature fluctuations. Repeated freeze/thaw cycles can cause soil heaving and be damaging, which is one reason for applying mulch around planted specimens (preventing those radical shifts in temperature as well as keeping the ground from freezing as deeply).
If you don’t get around to planting potted specimens before winter, you can either keep the pots in a cool location where it doesn’t get much below freezing, like an unheated garage, or heeling in as another poster suggested.
Make sure that dead-looking plants are actually deceased before chucking them. You can scratch a bit of bark off stems of woody plants to see if there’s any green tissue, which likely means there’s a chance they’ll resprout.