How do I winter over hardy plants in containers?

by Kathy Purdy on November 11, 2008 · 21 comments

in How-to, Mailbag

Not too long ago, a reader emailed me and asked,

I bought some hostas and dwarf bleeding hearts to plant. Shortly thereafter I hurt my knee and I can’t go out there and plant them. They are all planted in one gallon plastic pots. How can I safely winter them? If I put them in my garage they will still freeze.

You may have plants in containers that should have been planted, but weren't. How do you winter them over?

You may have plants in containers that should have been planted, but weren't. How do you winter them over?

It is the roots you are worried about freezing. The rule of thumb is that roots in a pot will effectively be in a situation two zones colder than plants in the ground. So if the plant tag says zone 5 and you are in zone 7 they should be fine.

But I’m guessing you live in a colder place. Definitely keep them outside until the tops die down. You want them to go dormant. After that, you want to put them in a situation where they will stay dormant but not get colder than two zones warmer than the hardiness zone on the tag. That will be different depending on what is available at your place. The garage might be okay, if it gets cold, but not as cold as outside. You could put them up against the house, and surround them with bags of leaves for insulation.

The other thing to consider is the greater the volume of soil in the container, the more insulation the roots will have. A one gallon container is not that big, and won’t have much insulating soil mix for the roots, so you might err on the side of caution and make that three zones warmer than the tag.

I have a drafty, dirt floor cellar that barely stays above freezing. I have put dormant plants in the coldest corner of the cellar and pulled them through the winter. They did start growing sooner than they should have, and made some pale spindly growth, but I very carefully hardened them off and planted them after all danger of frost. It was a pain in the neck but better than losing them.

About

Kathy Purdy is a colchicum evangelist, converting unsuspecting gardeners into colchicophiles. She would be delighted to speak to your group about colchicums or other gardening topics. Kathy's been writing since 4th grade, gardening since high school, and blogging since 2002.

In the end, this may be the most important thing about frost: Frost slows us down. In spring, it tempers our eagerness. In fall, it brings closure and rest. In our gotta-go world--where every nanosecond seems to count--slowness can be a great gift. So rather than see Jack Frost as an adversary, you could choose to greet him as a friend.
Philip Harnden

{ 20 comments… read them below or add one }

Bonnie November 4, 2010 at 11:33 am

I have about a hundred or so plants to over winter. I am in zone 3. Are there any suggestions.
Thank you

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Kathy Purdy November 4, 2010 at 12:29 pm

You have 100 plants in containers? What kind of plants are they? If they are annuals they won’t live a second year anyway, so there’s no point in trying to save them. After that, it is a matter of how much space you have, how valuable the plants are, and how much trouble you want to go to. Do you have a basement? An unheated garage? I would put the most valuable plants in the coldest part of your basement or the warmest part of your unheated garage. If you can’t fit them all in those spaces, then I would gather the rest against the least windy side of the house, stacking if necessary, then cover with leaves, hay, or any other organic, fluffy material you can get your hands on. Then cover with a tarp and weight the tarp down. And cross your fingers.

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peggy brooks November 28, 2008 at 3:31 pm

thx’s, great info,this I can utilize too, i’ll be using your website. happy holidays!! :) peggy

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Sue November 23, 2008 at 2:25 pm

Kathy,
I enjoyed reading this post and the replies. I overwinter lavenders and other herbs that I keep in pots all summer. So far, I have always gotten plants put in the ground that need to go there. I am thankful for my egress window, but a few did not fit in there this year. I was going to just use the herbs until they are no longer useable due to the weather, and hope for the best. If we get our garage cleaned out, I may try putting them in there. Thanks for the info!

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James Mann November 21, 2008 at 6:37 am

I didn’t realize that it was that easy to figure out, just two zones difference.

I was wondering how to winter my container plants but in a panic I decided to plant them all back into the ground for the winter.

My Great Aunt use to bring in some of here container plants, after they die down, and put them in the old attic. She would also go up to the attic a few times over the winter and give them a little water. They all seemed to survive the winter and looked great once they were back out side in the spring.

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Josh November 17, 2008 at 4:22 pm

Tedb and bogie are spot on…winter/spring freeze/thaw is a killer, along with being wet. Let the pots freeze and then keep them frozen (and dry) until spring. Frozen pots also reduce rodent problems, but if you are wintering a lot of plants baiting for rodents is a good idea.

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bogie November 15, 2008 at 7:46 am

Every year I have shrubs and perinnials that need to be overwintered. All I do is place them in a marginally protected area (next to the rugosa roses is a favorite place) let the pots sit there until they have frozen thru, then covered them with straw. I make sure to get a good batch of straw between the pots too, for good insulation.

What I am really after is to not let the plants thaw enough during warm snap in January that the plant starts to grow.

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tedb November 14, 2008 at 8:55 pm

Here in zone 4 all the small nurseries I know just tip the containers on thier side ( I think to keep moisture out) and then cover them with straw or a foam blanket. Most any covering that breaths should work I would think. I’d also put them on the north side of a building or an evergreen would be a good idea. It seems important to keep plants at a steady temperature. Death would be more likely from growing to early in spring, or during an winer thaw, then the raw minimun temp the pots reach.

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Kathy Purdy November 13, 2008 at 3:39 pm

Fran, I would believe it because I’ve forgotten plants myself. You are in a warmer zone than I am, so the evergreen snuggle was not as chancy as it would be for me. A lot of times we try something and cross our fingers, but we aren’t sure it works until after it does.

Annie, that thought had crossed my mind, but our sandbox still gets a lot of use and I would probably hear complaints.

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Fran Sorin November 13, 2008 at 3:34 pm

Kathy-
You’re not going to believe it but there have been times that I have literally forgotten to plant hostas or grasses on my top back bed in the garden before winter sets in. I just snuggle them in the corner under the protection of evergreens and believe it or not, they have done just fine hte following spring when I plant them up. Great advice given here….a much needed subject. Fran

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Annie in Austin November 13, 2008 at 1:12 pm

In the North I sometimes set hardy containers in a sheltered area up against the house and covered them in woodchips and leaves, but we didn’t have voles, thank heavens.

You know Kathy, thinking back, my favorite place to overwinter hardy containers was one originally made for our kids. When they grew older their old rectangular, in-ground sandbox was perfect! It was well drained and you didn’t really need to dig holes, just scoop out depressions in the sand.

Annie at the Transplantable Rose

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Carol, May Dreams Gardens November 12, 2008 at 7:13 pm

Kathy, good point about the roots, that’s what you want to be concerned about. It’s also good to water a few times through the winter if you have the pots stashed someplace where they don’t get rained or snowed on.

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Mr. McGregor's Daughter November 12, 2008 at 3:10 pm

I’ve had success with stuffing the pots in the window well & covering with a light laying of leaves. I think I may even have wrapped them in chickenwire once. One year when I had way too many pots, I clustered them together against the house in the corner by the chimney.

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Kathy Purdy November 12, 2008 at 10:19 am

Kent and Susy, wintering in the ground works, too, but I was working under the premise that they didn’t get planted because the gardener was injured. What should the gardener do with plants when he/she is unable to plant them, and winter is approaching?

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Kathy Purdy November 12, 2008 at 10:17 am

CottonM, point well taken about the voles. But I have had them get into potted lily bulbs I wintered over in the basement. (I had grown them from seed and didn’t trust them to the vagaries of winter.) Sometimes gardening is a crapshoot; you just do the best you can and hope for the best.

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Susy November 12, 2008 at 10:04 am

I have a raised bed in the back and I usually just put them in there over the winter. I occationally put them in the garage or the attic for overwintering. I’ve never lost anything.

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Kent Richards November 11, 2008 at 10:55 pm

I routinely winter over perennials in containers by simply heeling the containers into the ground. I usually bury them about half way and then mound up loose soil around them. When the ground thaws in the spring, it’s easy to lift the containers out.

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cottonM November 11, 2008 at 10:55 pm

I would be very careful about putting plants in leaf piles. These piles could easily turn into a nice winter mouse or voles condo with a full cupboard, especially in winters with nearly permanent snow cover. I’ve seen this happen a number of times with hypertufa troughs in Wisconsin.

What I have done several times is to take the potted plants and sink them in their pots in the ground. I do this out of direct sunlight to reduce heaving, sunscald, and desiccation. It’s important to have the top rim of the pot below the soil surface to prevent the pot from being isolated from the rest of the soil and drying out.

Presuming the plants are hardy they should do fine. If you are still a bit nervous you might mulch them but see the above.

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Dee/reddirtramblings November 11, 2008 at 10:05 pm

Really great post, Kathy. Here, which is much warmer, I store three and five gallon pots in the giant leaf pile. They overwinter great there. I also pull my other patio plants I want to keep up against the house on the east side. It’s only a couple, and they do fine.~~Dee

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eliz November 11, 2008 at 9:32 pm

Great post, Kathy! We all get these questions and wonder about this stuff all the time.

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