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brrrr! overwintering tips for tender plants

brugmansiaA THREAT OF FROST always sends me scurrying to haul in the last houseplants, something that if I were a better person, I’d have done a week or two before. Even if a particular weather warning proves a false alarm, it’s signal that it’s time: time to make plans for houseplants and other tender things like cannas and bananas, cordyline and a favorite pelargonium or two in hopes that what I call these “investment plants” (not perennial on their own, but carried over year to year with extra effort by me) are still around come spring. How to overwinter some favorite tender plants:

First, my general thinking: No two gardeners’ potential places to stash such treasures will match in temperature or humidity, so when I say the basement works well here, your cellar might not. I have identified my best spots by experimenting, and by killing many things in the process. But every year I score another victory or two because I don’t let failure stop me. (Isn’t all gardening like that?)

And this: If I don’t have the right spot for a plant–often a combination of high light but cool, 50ish-degree conditions–try forcing dormancy or semi-dormancy versus forcing it to limp along, suffering. If you have non-hardy plants you’ve tried keeping as “houseplants” in your heated home, only to see them go wretched and leggy, think about letting them rest, or close to it, next time. Water very sparingly and keep them as cool as possible.

Extra heroics: Adding a growlight hood for 12 hours a day in, say, a cool basement could make a so-so-storage space a really good one for many more things. Again: experiment.

houseplants

begonia and bromeliad indoorsFANCY-LEAF BEGONIAS: After a summer in the high shade of trees near the house, in they came (including ‘Marmaduke,’ above right, alongside a bromeliad). But first, as with all my “houseplants,” they get a physical: a checkup in the wheelbarrow (below) or on a tarp, one at a time, that includes a trim of any battered leaves, a gentle removal of endless spiders and the occasional tree frog trying to hitch a ride, and a wipe-down or rinsing off of the pots. Best to get all the houseplants in before the heat is on indoors to make the transition less abrupt, a transition instead of a shock to the system. These guys are tough, but resent drafty, cold spots; I try to find enough bright but protected places. Here’s how begonia expert Tovah Martin cares for her collection.

BROMELIADS: Bromeliads (including the Vriesea, below, and the one above left) are great in the shady garden all summer, and in the house all winter. I have had some of mine 10 years, and have only occasionally had to repot. I simply keep their “cups” filled with water all year. Talk about an investment plant.

CLIVIA: This Zone 9 South African relative of Amaryllis asks what many plants from that area do: Let it go dry and cooler in late fall to trigger the late-winter bloom cycle. I simply stop watering both my yellow and orange ones for two and a half months, and deliberately grow them in the mudroom, where the temperature shifts noticeably with the season; 50-60 is perfect.

houseplant in wheelbarrow
WITH ALL HOUSEPLANTS: Give them a physical (as my Vriesea is having, above, or as explained in the begonia paragraph); even then, you’ll import some bugs, but no big deal. Take care not to overwater (certain death) and do not feed in lower-light months, except with orchids that are out of bloom, which I feed alternating weeks. Don’t put anyone near heaters or too close to what will be ice-cold or drafty window glass in cold zones. Pebble-filled waterproof trays can add humidity to an area, as can clustering many plants or running a humidifier.

bulbs and bulblike plants

AGAPANTHUS: Traditional evergreen varieties (usually hardy to about Zone 7b) want that tricky combination of conditions that a cool greenhouse provides better than a heated home: bright light, and mid-40s or so, or as close as you can get. This is the hardest environment for me to simulate in my Zone 5B winter and heated home. Perhaps an enclosed porch, mudroom, or windowed basement (or bright garage if yours stays in the mid-40s or a bit warmer) can provide this where you live. They also want just enough moisture to keep them from desiccating, but not ever to be wet. Go easy. Those that are non-evergreen, with less-thick leaves, will go dormant, and are easy to overwinter here. Place pots in the basement or another cool spot; no light or water required.

AMARYLLIS: In mid-August or early September, I begin withholding water as I will for eight weeks or thereabouts, leaving the pots in a closet in the dark. I’ll take them out in mid-October or so, top up the soil if needed, and water once, then place the plant in a bright spot until it wants to grow. No trying to coax a sleepy amaryllis with repeat waterings, which can rot the bulb. Wait a few weeks or even a month before trying again, and once a shoot of some kind appears, begin to water regularly.

begonia-bonfire-2009
BEGONIA ‘BONFIRE’: The B. boliviensis selection ‘Bonfire,’ above, like its cousin ‘Bellfire,’ is a tuber, and wants to dry off and rest and unless you have ideal conditions (like the nearby greenhouse I have seen them prosper in all winter). For most of us, it’s just easier to let it sleep. I put mine in my 45- to 50-degree basement in the dark, pot and all, remove the withering foliage, and just let it sit, no water. Watch in late winter or earliest spring for hints of awakening: tiny sprouts at ground-level. Bring it into the light then and water very carefully until fully awake. Rot from overwatering (sometimes made worse by too-deep planting) is the easiest way to kill one of these in any season, but especially when just emerging and when it wants to take a nap.

TUBEROUS BEGONIAS and CALLA LILIES are easy to store, after a light frost (not a hard freeze!) signals to them it’s time to begin going dormant. The former are best stored right in their pots, cool, dark and dry; the latter don’t care so much about the cool part of the equation. Tuberous begonia and calla how-to with expert Dugald Cameron.

CANNA: These are the easiest of the easy, I think. In Zone 6 or colder, cut back frosted foliage to about 6 or 8 inches (or do this in late fall if no frost happens), then dig the rhizomes. Shake off the excess soil or rinse if you prefer. Divide into clumps of three to five eyes if really large, and place in the basement (or somewhere 45 to 55 degrees) in plastic bags left slightly open or perforated for air. Adding peat to the bags may help, but frankly I always dig up so many that losing a few is no cause for worry. And then I wake them up like this.

DAHLIA: Wait two weeks after a hard frost before cutting stems to 6 inches above the ground and harvesting tubers carefully. Note: The wait is essential for these succulent tubers to be ready to store; if there is no killing frost, I dig in November anyhow. Wash clumps, then dry in an airy, protected spot for a day or two to cure. Store tubers layered in boxes or crates (but not in plastic) in sand, peat, wood shavings or vermiculite at 40-50 degrees, checking for any signs of decay once or twice during storage.

Though dividing can be done before storage or in spring, big clumps may be hard to store; you can at least cut them in half and wait another day or two for cuts to heal before stashing. Kathy Tracey of Avant Gardens Nursery stores them in her New England location this way. Swan Island Dahlias has expert photos of how to divide.

colocasia esculenta mojito
ELEPHANT EARS is the name people give to both Colocasia (known as taro; the “elephant-ears” with typically matte leaves like ‘Mojito,’ above) or Alocasia (generally, these “elephant ears” have leaves that are shiny). Confusing, as storing them can sometimes be, since varieties on the market vary in hardiness from tough 7B-hardy types to true tropicals, meaning they have very different tolerances.

It’s particularly tricky if you live in a cold zone where the tubers often don’t get enough summer heat to really size up. Some new varieties don’t produce big tubers at all. Small tubers don’t have enough reserves to survive, dug, all winter long, so are best potted up (or left potted up) and stashed in a cool basement.

“The entire group of new elephant ears tend in that direction,” says Tony Avent of Plant Delights Nursery, “hence they will never be sold as dormant tubers by most bulb firms. These are best if kept potted through the winter under one of two regimes…actively growing at over 60 degrees F and in good light, or semi-dormant at 45-50 degrees and kept fairly dry and as such, light is not as critical.” How I try to overwinter the matte-leaved Colocasia types.

Larger tubers of some more traditional shiny-leaved kinds, the Alocasia, can be dug, the leaves cut back to the bulb, and allowed to dry until dry to the touch before placing them in the 45-50-degree spot; some people put them in peat or vermiculite containers first.

water-potExperimentation required, and I mean experiment: I even tried setting the nursery pots of some Colocasia that I like to use in water gardens (above) in a big plastic tub of shallow water in the cellar one winter. They looked like hell, but grew back into good plants anyhow this summer.

EUCOMIS, or pineapple lilies, are dead-easy. From tiny ones to towering giants, I stash them all, right in their pots, dry and dark and cool all winter, then take them out come spring and water again. My growing Eucomis collection.

GLADIOLUS: After the foliage dies, harvest the corms and store dry in mesh bags with good air circulation at about 40 degrees, such as hanging in a basement. Check a couple of times over the winter for any signs of decay.

other tropicals

BANANAS: Container-grown bananas can be cut back to about 6 inches just after light frost and stored, pretty dry, in a spot that’s about 45-50 degrees, such as a basement. I always check things I’m keeping dry to make sure they don’t go too far and desiccate in storage; sometimes by February, I need to give a little occasional water. Bananas that were grown in the ground must be dug up before frost, which disturbs the root system, so do not cut back the topgrowth too. Instead, wrap the dug rootball in a plastic bag and bring the whole plant into the same kind of cool, dark spot as above, allowing it to dry off at its own pace, cutting it back before watering and growth begin in spring.

BRUGMANSIA: In areas where Brugmansia (top photo) isn’t hardy, the best tactic is to let the angel’s trumpet go dry and dormant in a 45ish-degree spot, like the cellar. It can get to be quite a giant in the ground or even in very large pots, though, and big plants are hard to store (or even get into the house or basement!). Eventually you face the reality of having to cut it back partway to even get it into storage. Mine’s going in the cellar lying down; Mary, a Zone 6 reader shared in comments recently that she stores hers right in her house this way; cut in half, and resting, in an out-of-the-way corner, leafless like mine in the cooler basement will be.

HIBISCUS: Many people in cold zones know to bring these tree-like plants indoors in winter, but then try to keep them growing. A more effective tactic if you have a cool spot, would be to encourage them to drop their leaves by letting the plant go dry (like the Brugmansia, above, then store the dormant plant in a 40- to 45-degree location. Check every other week to see if a little water is needed to prevent desiccation.

pel-vancouver-centennialPELARGONIUMS (fancy-leaf annual “geraniums” like ‘Vancouver Centennial,’ above, and scented geraniums, or even zonals): I interviewed the co-owner of the longtime leader in these plants, Shady Hill Nursery’s Joe Heidgen, about how to care for pelargoniums year-round, including various overwintering tips. If you didn’t take cuttings to root in August, the best way to have the freshest plants for next year, you can also use this tactic from the Royal Horticultural Society (very much like the way my grandmother kept hers in her cellar, all cut back to stumps and barely alive, though she hung hers from the clothesline in paper bags). Pelargoniums with any hint of weakness or disease should be destroyed.

CORDYLINE and PHORMIUMS: These are really pricey plants, and get so much better when big, so I’ve been trying storage tactics for years with mixed results. Bright and cool is the key here (like high 40s but lots of light; little or no water), hence my adding a growlight to one area of the basement this winter. If I were a zone or so warmer, a bright garage would probably work, but not here. Keep a careful eye out for pests, particularly in late winter, and be prepared to trim off dried leaves come spring, when they can go out early.

just-tender woody plants

japanese maple in fall
JAPANESE MAPLES or HYDRANGEAS or other small trees and shrubs that are just slightly more tender than your zone allows can be grown as pot subjects, the way I do my Japanese maples. I have several (including one above) that are technically hardy, but hate the ice and wind, so I wheel them pots and all into the unheated garage on a hand cart for the winter, once the frost takes their leaves and they are sleeping. No light needed. They stay there until sometime from mid-April to early May, and require water once or twice in late winter so they don’t dry out once the potting soil thaws. Every third year they must be potted up or root-pruned. I have two friends with amazing old hydrangea collections grown just this way year after year.

FIG TREES IN POTS: Lee Reich has grown more figs up North than anyone else I know. He has tried every method from tipped over in the ground and mulched, to dragged into the cellar in pots, dark and cold (or even without their pots), to in the ground inside a barely heated plastic greenhouse, just above freezing. Overwintering potted figs, with Lee Reich.

CITRUS IN POTS: Since they are evergreen and also ripening fruit over the winter, these are really tricky for me, but cool and very bright is what’s wanted.        Overwintering potted citrus, with leading source Four Winds Growers.

ROSEMARY: Here’s yet another “cool and bright” subject, my biggest challenge in a cold Zone. How longtime herb specialist Rose Marie Nichols McGee of Nichols Garden Nursery advises we overwinter rosemary, indoors or out–depending where we live.

more information:

  1. Katy L says:

    I’m in northern vermont zone 4 so juicy succulents will not make it in the ground. I do a large variety of hardy sedums in my rock gardens. I just often wonder is there a better way to winter over those non hardy succulents? Window sill sun just doesn’t make it. Usually I limp thru with scraggly plants, put them out in spring and they come back to life as the summer wears on. And then I’m faced with the same old predicament…..

  2. Gay ayyagari says:

    Help…brought my tropicals in off the deck and into the morning room. Now I have ants crawling on the floor. What to do besides the borax/honey concoction to get rid of them?

  3. Karen says:

    I was just at a talk at our Botanical Garden on Brugmansia, and the speaker said when you cut it down to bring it inside to save and root the top that you have cut off, not save the bottom that is in the pot. The bottom part will not flower until it sends out more lateral shoots. That it will be a long time before it blooms and will get very tall. He said that he cut off the top and threw it away for many years, and finally learned that was wrong way to do it. He hybridizes Burgs and has about 800 in his basement. I am going to get my first Brugmansia this year and give it a try. I am zone 5.

      1. Ruby Jung says:

        I was introduced to Angels Trumpet in Southern Illinois by this method (rooting cuttings) in the 1980’s. It worked fine for me.

  4. Marie says:

    A 45- 50 % basement would be ideal – but I can’t help wonder why a basement would be that cold unless the house was poorly insulated or you left a door open.

    1. margaret says:

      Hi, Marie. Some of us in old houses still have unheated basements (with stone foundations and such), or at least a space within the basement that’s like that (like a “bulkhead” beneath the exterior basement Bilco doors).

      1. Eileen says:

        I too have an old house with an unheated, stone foundation basement. I have been over wintering various plants in this space for many years. Each year I say I’m not going to do it again but I always do. Thanks for your Tips Margaret, about different methods for different types of plants.

        1. margaret says:

          You’re welcome, Eileen. I always look at the really heavy things and say, “What, you again?!?” but then I go ahead and struggle to get them under cover somehow. I’m always glad come spring that they are still with me.

  5. Colleen says:

    Speaking of overwintering…can you overwinter ornamental grasses? I have tried to do this, but haven’t had good luck. I will try again this year but would like any suggestions. Thanks

    1. margaret says:

      Hi, Colleen. Most of the ones I grow are hardy (so they stay outside in the ground). But with something like purple fountain grass (Pennisetum rubrum), which is hardy to like Zone 9ish (meaning I think about 20F), finding the right spot is trickier than storing a dormant canna bulb! You might get some hints in this story (again I don’t know where you are and what grass).

  6. Joan lane says:

    I have a stag horn fern that has grown outdoors all summer. It is in a wooden hanging basket. What can I do to keep it alive this winter here in the mild winter state of Wshington?

    1. margaret says:

      Hi, Joan. The tricky part is the lack of humidity in the normal home (compared to a greenhouse). The staghorns really do badly in dry conditions.

  7. Andrew says:

    Hi, Really glad I found this post – lots of great information here! I live in Calgary in Zone 3 and we can get snow any time from early October (but likely November). I recently bought a Japanese Maple (Acer Palmatum Orangeola) as it was heavily reduced – I figure at worst I get to enjoy a few months of colour on our deck.

    Obviously my zone differs to yours so in terms of when I bring it inside, should it just be when it has dropped its leaves or is there a certain temperature at night that I shouldn’t have it outside for – should I be staggering bringing it inside? Presumably if it is due to snow it should be moved inside.

    I plan on keeping it in my garage which is pretty cold as it is unheated.

    Any advice you can give would be really appreciated!
    Thanks
    Andrew

    1. margaret says:

      I wait till the plants are dormant (the maples and other woody things), and have dropped their leaves. Then they can go in any time — but you are right, probably before it’s hard to move it with possible snow or ice, or the pot freezes and breaks, or the pot freezes to the ground! :) Sounds like you could get away with sometimes late October or early November easily, provided a big storm isn’t coming first. I roll mine to just outside the barn, and then when the bad weather finally threatens, roll them the rest of the way inside.

      One important point: In your Zone 3, an unheated barn like mine (I am in Zone 5) would get down to almost the outdoor temperature, which in your case is too cold for these plants. They are mostly Zone 5 hardy, and in pots things are a little less hardy because their roots are up above the insulation of the earth. So I am not sure how they will fare in the garage in Zone 3–it very well may kill their roots.

      For you they are not hardy outside; for me they are almost hardy (but get damaged by ice, winter wind, and late frosts). So that’s the difference — is there any other just slightly warmer storage possibility?

  8. Carole says:

    So much wonderful info..I agree with others,really is one of the very best places to be for reliable information..and meet pleasant people..

  9. I sokol says:

    I over winter my hydrangea in my unheated garage by placing the pot it grows in into a larger pot and pack lots and lots of leaves around it as insulation. I have a mum treated the same way. So far it works. This year I have many pots that have various ground cover plants in them that I will try to over winter. Not sure how I am going to this. I’m in Ohio, I think zone 5ish. Living in a condo leaves me not many choices as far as saving plants.

  10. Poulsbo Garden Lady says:

    Hi Margaret,
    I just wanted to share a success that I have had for two years with overwintering Colocasias in pots here in the PNW where we admittedly have milder winters. I securely wrapped and taped my pots with bubble wrap, extending the wrap about 8 inches above the height of the pot, then filled the top of the pot with loose straw. I dragged the pots under the deck, next to the house for the winter, and brought them out in the spring when new leaves peeked through’. This has worked twice for me but now I have the problem that my colocasia tubers are rootbound so will have to dig them out and repot…fingers crossed!

  11. katy says:

    what’s the best thing for tender succulents? I put them out all summer and they thrive. then I bring them in and by mid-winter they’re scraggly and sad.

  12. Marge says:

    I have a suggestion about overwintering Purple Fountain grass. I have taken the grass out of the large containers I plant them in in fall, divided out some small plugs that are clearly still alive and growing and planted them in small pots. Then I cut the grass back and place the pots under lights in my cool basement ( I don’t really have sunny windows in my house). They grow just fine and I just clip the grass back if it gets too tall. Then I have several smaller plants I can put out in the garden in spring. Seems to work fine.

  13. Chris mid-Hudson Valley says:

    I have great luck carrying over dahlias by lifting the tubers, all dirt intact, and putting them in large plastic pots, usually lined with plastic bags for the sake of neatness. They’re stored in a nearly unheated upstairs closet that hovers around 45 – 50 F in deep winter. The plastic bags stay open until the soil is almost completely dry. Then when they begin to show growth in early spring, they go into a cool but very sunny porch to start growth; I top up with good soil and poke holes in the plastic bags. When the weather warms they go straight from pots to beds and I have flowers by late June. With some I skip the sun-porch step and settle with later flowers. I’ve never lost a plant.

    Like Margaret, I have great luck carrying over dormant Begonia “Bonfire” stored in the dark in the same cool place as my dahlias. Started early on the same sun porch, it makes a 4-foot drooping pillar of color by late summer.

    1. margaret says:

      Thanks for the extra help with overwintering tips, Chris. Sounds like you have the dahlias really nailed, and the ‘Bonfire,’ too. Nice to hear from you.

  14. Candace Langford says:

    Fortunately most of these plants overwinter in my area (NE Georgia), but I do fill the basement with tender elephant ears in pots. It’s November here, and still in the 80s with low 50s at night. Anything marginally hardy I put in an unheated “greenhouse” that I made from an old storage shed. I put flourescents in the basement and reserved two rooms for plants. I bought a heavy duty roll cart for moving bigger plants.

  15. Helen Malandrakis says:

    I have had success cutting back the foliage of my cannas and then covering with a lot of leaves.
    They have always come back. I live in Indiana. Zone 5b-6.

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