overwintering tender plants, with kathy tracey

Stashing tender plants (a doodle by Andre Jordan)ARE YOU JUGGLING the tender plants, playing a game of “Beat the Clock”—or is it “Beat the Mercury”—as temperature increasingly dip? I asked garden designer and nursery owner Katherine Tracey of Avant Gardens, known for pushing the limits of hardiness in her landscapes and nursery, for some advice on overwintering.

You may recall the popular interview Kathy and I did about looking at our own gardens with a critical eye to design improvements. (If not, it’s at this link.)  We also spoke on my radio show and podcast on Oct. 13, 2014 about what to stash and how, and what to toss, just as temperature at her Massachusetts location at Avant Gardens and mine were flirting with the mid-30s at night.

Plus: Links to in-depth articles by Kathy and by me on aspects of overwintering–from succulents to figs, and even if you started earlier by taking cuttings from things like coleus–are at the end of the page.

overwintering q&a, with kathy tracey

Katherine Tracel of Avant GardensQ. I know you have greenhouses at Avant Gardens, but nobody has infinite space—so how do you even decide what gets a winter home?

A. As far as the nursery goes, the plants that we propagate from and can’t find a wholesale source for, or can’t count on finding a steady supplier for, definitely get made room for.

Q. Your “Mama” plants have to be accommodated first.

A. Yes, we prioritize them, and for the homeowner, the same thinking applies:

The plants that can’t be had easily and that they don’t want to lose.

Q. Hard to get, expensive, or both.

A. And also something perhaps that is of size—and this is the tough one. Like Phormiums, which get better with age, take several years to develop into wonderful clumps, and you can’t buy them locally. So that would be a plant I would put on the top of my list to keep.

abutilon standardQ. So I have to confess right off the bat: I broke your first rule. I had some really big variegated Abutilon standards [detail above] and other things too big for me to store, and I called a friend at a public garden and said, “Timothy, do you want to adopt these babies?” [That’s him below in my driveway, taking plants in his van to Untermyer Gardens in Yonkers, New York.] Do you ever do that, like a museum that is de-accessioning things?

tender plants being adoptedA. One year we donated a group of succulents to the local elementary school that had these big south-facing windows with a nice ledge, so the children go by and look at them. They were looking to do something in that space; it was just calling for it. Something alive.

So that’s a possibility: donating to schools, a small business, a coffee shop with sunny windows.

Q. It does feel bad to throw them into the compost heap.

A. Sometimes it’s not a matter of economics, because when you think of all the care that goes into preparing the plant for winter, trying to keep them going all winter, dealing with any pests that occur—all that adds to the actual cost of the plant. When you think, gee, maybe you can find it next year at your local nursery for $10 or $15, even if it’s not so big, you’ve relieved yourself of all that responsibility.

succulents being storedQ. You mentioned succulents you donated to a school, and you have a special expertise in and fondness for succulents (and lots of frost-tender ones in your catalog, in addition to hardy types). What about stashing those, the non-hardy ones? You’ve really pushed the limits for our Northern gardens.

A. They’re really easy. They don’t need a lot of water—but they do need light, which is the tricky part. But they can take cool temperatures. So if you have an older home with an attic that stays above freezing, but has a south- or west-facing window—you could put them up there. Again: they don’t need a lot of water.

I wouldn’t say put them up there and forget them until next spring, but you can be creative in finding spaces for them.

[Kathy takes apart too-big-to-store succulent planters if needed, potting them down to smaller containers, photos above; all her succulent-stashing tips are here.]

Q. Above freezing, but bright light.

A. In Southern California, where you see these plants growing outdoors, their days even in winter are longer than ours. You may get some stretching in the spring—which is another topic: what to do when get gangly. My recommendation is to cut them back then, and wait till they sprout anew, and they will do that. You just have to be brave.

Q. These are Zone 9 plants, so they want to stay above a certain minimum….

A. …yes, 35 or 40ish, but one year in the greenhouse the furnace died, and it got down to the 20s. You see what lives—and actually a lot of things do—but they may not look very pretty for awhile, till the topgrowth comes back.

Q. You just said your furnace went out one winter. I think it’s important for people to realize: Stuff happens! Pushing the limits is always an experiment, a test drive. Year to year, temperatures and humidity in storage spaces may shift, because the outdoor weather does.

A. It is an experiment. You’re dealing with nature and living things. Seasoned gardeners learn to go with the flow—we only have so much control, and then we don’t.

For instance, I tell this story to people and they look at me, like, “What?” We sent our son off to college, and he wanted a plant, one of the elephant ears or Alocasia.

He kept it alive, barely, through six years of moving from college to homes to apartments, and then all his stuff got pushed into the garage one year. And the Alocasia lived in the garage one year, without water, without care—with nothing, in the darkness for over a year.

It had no leaves; it was just a brown stump in a big clay pot.

I decided to empty it out and dragged the pot out, but it just sat there for awhile before I got to it, and wouldn’t you know: all of a sudden a sign of green just pops through. The next thing I knew it’s beginning to unfurl—after a year without anything.

cannas-from-bagsQ. They want to live.

Some things are dead easy, like cannas [above]—which give you more each year, and I just dig them up and drag them into the cellar in bags (which I don’t tie closed) and no problem. Other bulb-like things are trickier. Like dahlias. You’ve grown a lot of dahlias in the garden this year so what’s the plan with those, as frost knocks on the door?

A. You wait for the frost to blacken the foliage, then cut back the foliage and dig them up.

This is where you have to be very carefully; if you pierce the tubers, you create a wound that might invite infection and spoilage, fungal problems.

One: Be really careful digging them up.

What the books will tell you: Dig the roots, rinse off most of the soil. Then put the roots in a dry spot–a garage, a greenhouse; in the sun or out of the sun. They’ll dry quicker with bright light. Some people actually take the roots after they’re cleaned and hang the roots upside-down so that the moisture isn’t collecting in the stem, and is drawn out.

Q. Sort of curing the stem end.

A. Yes. And I should say, because I have forgotten to do this: Make sure if you have more than one variety that you label the roots! [Laughter.] You can’t tell dahlias apart when they’re dormant.

When they’re dry, you want to store them in a ventilated box—a wire mesh box, a wooden crate, or even a plastic box with holes drilled in it. It’s the trapped moisture with dahlias—fungus and dahlias don’t go together, and the trapped moisture is where you run into pathogens.

You’d line your container with wood shavings, or peat moss that is barely moistened with a spritzer from a spray bottle. Or I use a woody-plant potting mix that has a lot of bark in it and is very well-drained, to layer between the tubers.

Q. Temperature?

A. Cool; anything below 50, so like 40 to 50F.

Sometimes I just pot up a big clump, once it’s dried and cured, in a big pot of this very well-drained soil mixture, and keep it under the greenhouse bench, unwatered.

Q. Not watering it, or allowing it to be warm enough to wake up.

A. Yes, this is why cool is better—so the moisture doesn’t dry out in the box.

I don’t use fungicides here on the dahlias, but there are some biological ones—though some people are very sensitive to sulfur and copper, so I am always telling people to be very careful and read the instructions before they use them, and wear gloves.

[Dahlia ‘Corona,’ an Avant Gardens favorite, is at bottom right in collage below.]

Boone glad, Oxalis triangularis, Corona dahliaQ. Any other bulbs you recommend as “investment plants” that are dead easy to carry over? I’m loving the pineapple lilies, or Eucomis. I just stash them, dry in their pots, all winter in the cool cellar, then bring them out and water again in spring. Any other to try like that?

A. Oxalis triangularis [top right in photo collage above], which is not hardy enough for our Zone 6 winters, but can be perennial in Zone 7. You can just bring the whole pot inside, or separate the bulbs and store them in Ziploc bags in some dry peat moss in a cool, dry spot.

Any of the species gladiola, too. We’ve had luck with the form ‘Boone’—like Daniel Boone, but Gladiolus dalenii ‘Boone’ [above left]—a pretty, smaller form with apricot flowers that can be grown from seed, and multiplies quickly. You get a lot of offsets in the first year. You can try leaving in the ground in Zone 6 or warmer, but you can also lift them, and store them in a pot of soil, or just putting them in baggies with the peat moss.

Q. I mentioned early on that I gave away my Abutilon standards—but what could I have done with an Abutilon if I had wanted to keep it?

A. You can cut normal Abutilon back really hard and just store the pot with the roots. Anything that has foliage growing on it is going to want to photosynthesize; it will want bright light.

copyright Avant GardensQ. So if they had been a regular pot or hanging basket, not a standard, I could have give them a serious haircut. And then brought them indoors, into bright light?

And what about pests on overwintered plants?

A. It’s not a bad idea, especially with very bushy things, to cut them back before bringing them in. First, you reduce the amount of light the plant needs, and second you remove possible pests harbored in the foliage, and it will be easier to get at what foliage is left.

We use Safer’s soap, and Neem, and kind of rotate the two. They do a really good job, and Neem has some fungicidal qualities as well, so that helps with things like powdery mildew spores that are still harbored.

houseplant in wheelbarrowQ. I set up a triage unit in a garden cart by my door [above], before we bring them in: clean off the pot and plant, remove any nasty leaves, cut back if needed, look for insect pests and such. I really just eyeball the plant carefully before carrying it into its winter home. Thanks, Kathy, for all the advice.

more overwintering how-to from kathy tracey

overwintering from a way to garden archives

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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

(Doodle at the top of the page by Andre Jordan.)

  1. Irene Di Maio says:

    Thanks about the advice on overwintering. This spring my sister gave me a flowering fern which I would like to overwinter. Have an unheated garage and a cellar. What do you recommend? Should I cut down the leaves? Wash off the roots? Or just store as is?

  2. Maryfran says:

    I would like to overwinter salvia greggi in my house I’m told it is a perennial not hardy here in zone 5. I want to do it so it is big and beautiful when the hummingbirds arrive in April. I can put it in an unheated attached garage or an unheated bedroom, warmer than the garage but coolish. Any experience doing this? Should it be cut way down or just slightly?
    Thanks for any advice.

  3. Alejandro says:

    My list of easy to overwinter tender plants (my zone is 5b) also includes Euphorbia cotinifolia (not a bulb. I just keep the pot in a dark, dry, above freezing cellar. It’s such an excellent foliage plant), Gloxinia nematanthodes (it multiplies quickly, leave the bulbs in a pot anywhere above freezing, dark and dry is OK), crocosmias (some are hardy, most are borderline. A pot in the dark above freezing works). I find that Nerine bowdenii and Impatiens tinctoria are easy to overwinter but in my zone you need to start them very early (February) for them to bloom, if they’ll bloom at all. Salvia patens, even if it’s herbaceous, can be treated as a dahlia, I find it works best to keep just the roots in a pot with soil in a cool, dark place. It will need some water during the winter not to shrivel.

  4. Dixie says:

    Re the abultions. I have a small collection of 7-8 varieties and when they are greenhouse bound for the winter after spending the summer planted in either raised beds or deck pots, I cut them back and propagate for friends. It is also a bit of insurance in case of Mother Plant failure. Don’t forget to label !

  5. Anna says:

    This is a great article, especially the part about how it feels to toss things into the compost bin! I don’t do a lot of saving, although I do save a lot. I don’t feel bad about it either, LOL! I don’t save pelargoniums for example, but I will take cuttings of peppers if they produced well that year and I liked what I ate. Because it snows and is very cold here in central MN for a good portion of the year, tropicalesque gardening has appealed to me greatly and that does mean I bring in a lot of things for the winter. But again, I do toss a lot. :)

    I do like the tip of pruning back some things hard (like abutilon) as window space here over the winter is at a premium and if I have something I want to save that can go without bright window space, that’s a good thing.

    The storage ideas were great. I love learning how others store their bulbs, tubers, and corms etc. Glad to know it’s not an exact science, but certainly some amount of care is required to ensure those tubers make it through storage.

    Anyway, great post, timely as always. I enjoyed reading!

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