Herbaceous perennials in pots — plants that die back and are dormant in winter — that have been part of your summer container displays need to be protected over the winter if they’re going to survive and bloom again next year. Here’s how to overwinter perennials in pots.
Hardy perennials have roots that sleep until next spring, which is when they begin to put on new growth. A few examples are hostas, Shasta daisies, heucheras, astilbe, lady’s mantle and daylilies. To overwinter them successfully, you need to keep the plants dormant and provide a winter environment that’s within their hardiness zone. A plant growing in the ground is more protected from severe cold (and alternate freezing and thawing) than one in a container; therefore, a plant that’s hardy to your zone usually needs extra protection if left in its container.
After a couple of killing frosts, water plants thoroughly and choose one of the following three options for overwintering:
Option 1. Leave the planted container in its current location. If the container is large and able to withstand the elements, and if the plant is at least one zone hardier than your area (i.e., if you live in Zone 5, herbaceous perennials in containers need to be hardy to Zone 4 or lower), the likelihood of successfully overwintering the plant in its pot outdoors is high. A large container holds more soil, which helps insulate roots and keeps soil temperature consistent. However, when sun hits the sides of a container, especially a dark-coloured one, alternate freezing and thawing may trick the plant into thinking it’s spring and trigger early growth, when it’s merely a warm day in February.
Option 2. Move borderline-hardy plants or those in small containers to an unheated garage or shed to increase survival odds. Because the plant is dormant, light isn’t required for photosynthesis, but do check every couple of months to make sure the soil isn’t bone-dry. Don’t overwater, however, as this could cause plants to rot or break dormancy.
When growth resumes in late winter/early spring, reintroduce the plant to normal growing conditions outdoors by gradually exposing it to the elements for increasing periods of time.
Option 3. Find an area where you can sink the plant and its pot into the ground so the roots will be better insulated. (A vegetable garden often has unused space.) Cover the plant with two to three inches (5 to 8 cm) of winter mulch, such as shredded bark or leaves. In spring, remove the mulch and lift out the container.
If you wrap the planters in burlap and cover the top with woochips, will the flowering plant servive winter? Thank you.
I have 4 Alberta Spruce in planters and would like to know if I can leave them outside for the winter. What can I do to protect them from Ontario winters?
Hi Becky – I am moving from my GTA home in March and have several perennials, including a couple of rhododendrons, in plastic/wire pots (now in decorative containers) which I’m planning to take with me. I’m wondering if it would be a good idea to take them out of the decorative containers, leave them in the plastic/wire pots and wrap them with landscape fabric to keep the soil moist and together ready for transporting. I could take them now before the winter to a friend’s backyard and cover them with leaves as well. What would you recommend? Would a protected north exposure or more open south exposure be better? Thank you.
Hi Gail
We are scheduled to move in November and I want to bring my perennials with us – phlox, bachelor buttons, daisys, peony, astilbe, wind flower and roses. I have a friend who has offerred her raised bed veg plot to me for the winter. Should i pot these guys up or plunk them right in?
We are in Hardiness zone 5…coastal Maine.
I’d pot them up in moistened container soil in old plastic grow pots that have drainage holes, then plunge them into your friend’s raised beds. Cover the tops with two or three inches of shredded leaves. You can nestle them quite close together. The aim is to keep them from freezing and thawing throughout the winter. Remove them early next spring and replant in your new garden. Good luck!
I have had great success by getting ahead of the game and buying spray in foam that comes in a can and spraying the inside of the pot before putting soil in. I spray a one to two inch layer around the inside of the pot. Because you spray it on, any shaped pot can be treated. I did this 15 years ago to my outdoor pots and the foam is still holding up and my plants have lived very well.
If these excellent methods of keeping perennials is not practical, I have a suggestion that has worked for me for many years. I dig the, mostly trailing perennials, out of their pots, wrap all the trailing branches around the root ball and bury them deep in my compost pile. When we open the pile in the spring, voila, all the plants are alive and well. I cut off the dead trailings and replant in my pots. Works like a charm.
I live in southern Quebec, close to the Vermont border.j
I have very good luck overwintering plants even in small plastic pots. We have lots of snow & they get buried pretty deep.
I live in zone 5 (zone 7 depending on who you ask) on the coast of Lake Erie. I want to over winter potted perennials for the first time.I have black eyed susans as well as mexican heather in pots that I would like to save. Any advice would be appreciated.
Hello Gail
I am planning to try a trough garden using an old concrete laundry sink.
I am in the Alliston Ontario area, in a fairly sheltered valley Zone 4/5 ish.
I will be planting Alpine plants…….what should I do to insulate the whole trough over the winter…??? Would you recommend placing the sink on the ground or could I get away with insulating the space between the supports if I lift it up…???
dave
I am wanting to plant boxwoods in my tall plastic planters for the deck. I live in Saskatchewan where the winters can be a little harsh. Just wondering if you would know if they would survive a winter left in the planter on the deck .
Unfortunately, I doubt the boxwoods would survive your winters. Perennials and shrubs overwintered in above-ground containers need to be two zones hardier than your growing zone. Also, plastic isn’t a very good insulator.
How about plants in pottery or ceramic pots. Will they crack when the soil freezes? Also, if I plant spring bulbs in a pot and place it in an unheated shed, will it survive the winter? Should they be lightly watered during this time. Thanks
I’m trying Option 3 with some roses that I won’t be planting till next spring. I put the plants and pots in the ground and covered them with an extra 2″ of soil. They’re in an area that is sheltered from the wind and I’m also going to spread mulch over them. Do you think they’ll survive?
Hello, Gail: I think your roses have an excellent chance of surviving. By sinking the potted roses into the ground, you’ve provided necessary insulation to the root balls. Once the ground freezes and the plants are totally dormant, pile some shredded leaves or mulch over the tops of them for extra protection. Your aim is to keep the plants dormant until spring by preventing fluctuating winter temperatures from thawing, then freezing, the roots. It’s usually the alternate freezing and thawing that harms plants over winter, not the cold itself. Next spring, gradually uncover the tops to allow warmth and sun to reach their branches. Once the danger of hard frosts has passed, you can transplant the roses to their permanent locations.