8 Rules for Overwintering Plants in a Garage or Basement

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Overwintering pots indoors

Every year at this time, I am surprised by the motley group of containers that has accumulated in my basement for safekeeping through winter. This year there are the amaryllis bulbs I’ve been growing for ten years, the shamrock (oxalis) that summered outdoors, and sheared-back pots of chives, rosemary, and sage. Even though the space is chilly and dark, they will be safe and happy through the winter there, with minimal care.

I’ve been enjoying overwintering plants in garages and other cold spaces for many years, and while I’ve had many successes, there have been failures, too. Here are a few tips for overwintering plants in a garage or basement I learned through trial and error.

“Overwintering
Find a cool, dry place to overwinter dormant potted plants

1. Find a Good Overwintering Place

To be sure plants know it is winter, you need a dry space where temperatures stay above 45°F (7°C) but below 60°F (15°C). I once had a house with an attached unheated garage that worked well. In another house I used a minimally heated outbuilding, and now I have a basement. Light is not a factor for dormant plants, though weak winter light won’t hurt them.

2. Clean Up Containers Before Bringing Them Inside

With plants that have grown in pots outdoors all summer, I assume the top half inch of soil has gone salty, so I scrape it off and scatter it in the yard. Then I snip off dead plant parts, give the pots a quick wipe with a damp cloth, and move them into cold storage. After a few days, I check for signs of unwanted insects, earthworms or earwigs.

“Geraniums”
After a month of cool rest, many geraniums will resume growth and bloom all winter

3. Don’t Over-water Overwintering Bulbs

Many of the best plants for overwintering in a garage or basement have bulbous roots designed to store nutrients and moisture through a dormant period. Amaryllis, oxalis, cannas, dahlias, and tuberous begonias hold moisture in their fleshy bulbs, tubers and corms, so very little supplemental water is needed. I like to let the pots dry out thoroughly in early winter, and then dribble a little water into the pots every week or so in January and February.

4. Let Overwintering Plants Rest

Chives and geraniums benefit from a short dormancy period, so I trim back the plants and let them rest for a month or so before bringing them back to life in a warm, sunny window. Many other perennials can do with a longer rest period, and you can control when the plants start growing again by keeping them cool and dark. I let my amaryllis and oxalis rest through the holidays, and restart them in January for late winter fireworks. Container-grown asters and chrysanthemums purchased for fall display can be overwintered in a garage or basement, then transplanted outdoors when the weather warms in spring.

5. Avoid Temperature Fluctuations

Reduce the guesswork about watering by covering your whole collection of pots with an old blanket or flannel sheet. Also cover the plants when you temporarily heat the space for other uses. A cloth cover will reduce temperature changes and block light that might confuse the resting plants.

“Pot-grown
Pot-grown herbs and flowers like rosemary, sage and chrysanthemum are easy to overwinter in a garage or basement

6. Provide Good Ventilation for Happier Herbs

Some windows leak cold air, which compromises energy efficiency but feels pleasant and natural to rosemary, sage, and other half-hardy herbs. Exposure to chilly drafts seems to prevent rosemary powdery mildew, while meeting the plants’ needs for limited winter chilling.

7. Tackle Overwintering Pests Promptly

A few pests can persist in overwintered plants, so it’s important to trim off dead foliage before putting plants into storage. Be watchful for the webs made by spider mites, which can make a mess of resting strawberries that are holding only a few leaves. When you notice spider mites or any other pest, immediately move the plant away from the others to stop the pest’s spread.

“Freesia
A cool start improves the growth of fragrant freesias, grown indoors from corms

8. Force Some Freesias

When I have lost overwintering plants, it has usually been because I forgot about them too long and let them dry to toast. This never happens in years when I pot up a few freesias and let them chill in the basement for a month, because the awakening corms demand to be checked upon once a week. Adherence to duty brings beautiful, fragrant blossoms when the plants are moved upstairs and allowed to grow in a sunny winter windowsill. My other overwintering plants get better care by being friends with freesias.

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Comments

 
"I'm in Zone 5, so I'm already thinking about overwintering. :( I noticed you mentioned that you look for signs of earwig or earthworm activity after you bring your containers inside. I assume you just take the worms outside but what would you do about earwigs? "
Sonja on Tuesday 21 September 2021
"I am in zone 8. My ammarylis are outside with long leaves if I bring them into the garage at 48 degrees, will they bloom in late Nov. or Dec.?"
Ramona Diane Stratmann on Tuesday 12 October 2021
"I am thinking of putting up clear plastic in a portion of my garage to put my lantana and my chrysanthemums that I have grown this summer. The garage is unheated and I plan on using a heater to keep the temperature at 50 degrees. Could you please give me some advice? Thank you in advance, Phil"
phil on Friday 16 September 2022
"I have cut some lantana’s so I do not have to buy them next year.I cut below each nub,dipped them in hormone power and put them in pot soil in little pots in the garage.Do I need to water them thru the winter? Or is there anything else I need to do?"
Becky Graham on Sunday 23 October 2022
"I have a Rio flower for the first time and it’s absolutely beautiful. I live in Ohio and I know it won’t survive the cold winter. I have read that I can keep it in my garage covered lightly to preserve til spring. Can you confirm? Thank you! "
Petey on Tuesday 25 October 2022
"I have overwintered several flower plants in their original pots in a cold and dark fruit/wine cellar in my basement with winter temperature above freezing and up to ten Celsius. I have had some success last year and am familiar with most procedures, but I am not sure of what to do with the long shoots growing even at this cold temperature and dark environment of several potted plants? Should I cut them down or leave these shoots as they are? It's way to early to take them out on a Canadian Winter, not until late April or May Zone 5. Thank you for your feedback "
Danny on Friday 20 January 2023
"Ramona, I think that because amaryllis enjoy such as long growing season in your climate, they will be prone to blooming in spring rather than winter. You can put them in the ground and grow them as perennials! "
Barbara Pleasant on Monday 30 October 2023
"Becky, I hope you had good luck with your lantana. Ideally they had some roots on them before going dormant? Next time I would cut back the mother plant by two-thirds, overwinter it in your garage, and move it to good light first thing in spring. Then propagate the new growth that pops out from near the base. "
Barbara Pleasant on Monday 30 October 2023
"Petey I agree that the Rio Dipladenias are gorgeous! They are grown from rooted cuttings, so you would try to get the parent plant through winter, and then pot up pups that regrow from the roots in spring. Worth a try! "
Barbara Pleasant on Monday 30 October 2023
"Thanks for your comment, Danny. Some overwintering plants just don't get the memo and insist on regrowing when they should not. Cannas do it every time! The low light shoots are probably not hurting anything, so I tend to leave them alone. "
Barbara Pleasant on Monday 30 October 2023

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