Overwintering perennials in containers

Most people consider spring the busiest time in the garden, but fall is the real crunch time for me. At least in spring, what doesn’t get done one week can usually be delayed for a few days with few consequences. However in fall, what doesn’t get finished one week may never get finished at all if there is a hard frost or a few days of freezing rain.

As well as cutting back peonies and hostas, overseeding and feeding the lawn, banishing the worst of the weeds, clearing out spent annuals and vegetables, digging up and storing tender tubers (dahlias, cannas, etc.), and planting bulbs, decisions need to be made on how to overwinter herbaceous perennials that have been growing outdoors in containers. In addition to perennials, I also have a few clematis in pots to store.

First, make sure the pots your plants are growing in can survive freezing temperatures. They also need to be large enough to hold enough soil to insulate the roots. Secondly, perennials overwintered above ground need to be at least two zones hardier than your growing zone. For example, I garden in Zone 6, which means any perennials I overwinter in containers need to be hardy to at least Zone 4, although I have gotten away with Zone 5 plants. No guarantees, though.

Thirdly, find a sheltered spot where temperatures remain relatively consistent, away from sun and wind. It’s not cold days that cause failure, it’s warm, sunny days that tempt plants to break dormancy that are then followed by freezing temperatures that wreak havoc.

Perennials, clematis and roses don’t need sunlight over the winter, because they’re dormant. I use the back walls of our garage and screened porch that are attached to the house for the pots of hostas and clematis I overwinter. These have been good spots for miniature roses in pots, too. Once or twice in winter, I’ll check the pots for moisture. If the soil is bone dry, I’ll add water.

In my experience, the trickiest plants to overwinter in pots are broadleaved evergreens, probably because their leaves desiccate (lose water) so readily in winter.

For more options on overwintering perennials, see “How to overwinter perennials in pots.”

Garden news and views

• Lee Reich is an expert on pruning. Reich calls himself an “avid farmdener,” something he defines as more than a gardener, but less than a farmer. His latest post “Hardwood cuttings: not hard (to do successfully)” offers details and diagrams for how to take cuttings of blueberries, kiwifruits, grapes, currants and plums.

• Gardeners in Ontario who keep a diary of what’s going on in their garden look forward to each new edition of Toronto & Golden Horseshoe Gardener’s Journal. The 30th edition for 2022 is out now and can be ordered at gardenjournals.ca.

• If you’re looking for advice on how to prompt your short-day houseplants, such as poinsettia, kalanchoe or Thanksgiving cactus, to rebloom, Larry Hodgson (The Laidback Gardener) has tips at “Short-day houseplants need special fall treatment.”