- Gardening How-to Articles
- Overwintering Potted Plants
- Thinking Regionally
- Container Care
- Preparing Plants for Winter
- Winter Protection Techniques
- Overwintering Pretty Potted Perennials and Shrubs
- Protecting Potted Plants over Winter
- 10 colourful winter pots
- Winter veg and herbs for containers
- WHERE YOU NEED TO PROTECT YOUR POTTED PLANTS
- ZONAL WINTER PROTECTION
- WHAT YOU NEED TO OVERWINTER YOUR POTS
- TIME TO WRAP!
Gardening How-to Articles
Overwintering Potted Plants
By Shila Patel | September 1, 2001
Fortunate are gardeners in mild-winter regions, where container gardening is a year-round pleasure without the threat of shattered pots and frozen plants familiar to many of us. Compared with their garden-grown counterparts, container-grown plants are at a severe disadvantage when cold weather arrives. Though hardy plants have developed foliage, stems, and branches that can withstand very low temperatures, their roots are far more sensitive and vulnerable to freezing.
When planting in containers, even choosing plants hardy in your region is no guarantee that they will survive the winter. Many experts suggest that to better the odds of a plant’s survival, choose one marked as hardy in two zones colder than your area. For example, if you garden in Zone 7, choose perennials, trees, and shrubs marked hardy to Zone 5 to increase the chance that the plants will survive the winter. When possible, use large containers for plants that must remain outdoors—the greater volume of soil surrounding the plants will provide increased insulation around the roots.
Luckily for gardeners in mild-winter regions (the warmer parts of Zone 8 and south), container-grown plants require little or no winterizing beyond moving pots to more sheltered locations and perhaps covering them with frost blankets when freezing temperatures are expected.
In colder regions, where freezing temperatures are the norm at the height of winter, gardeners must protect plants from both the cold and the wind using a range of techniques. Overwintering container-grown plants outdoors is extremely challenging in the coldest regions of the country (Zone 4 and colder), where it’s best to grow annuals and perennials for one short season of color.
In all but the mild-winter regions, potted plants grown on terraces and rooftops, where they will be exposed to chilling winds, should be moved to a sheltered location, such as close to a building or near a pergola or other structure, away from high winds and winter sun. When possible, group pots together, placing the most cold-sensitive plants at the center of the group, so they receive additional protection from the hardier plants.
The first step for winterizing the container garden is to clean and tuck away any empty pots. Store clay and terra-cotta pots upside down or on their sides in a dry place. Because they are made of porous clays, most terra-cotta pots are not suitable for leaving outside in freezing temperatures, which can cause them to crack or shatter. If you must leave terra-cotta pots outdoors, choose ones made of special clay that tolerates freezes (like Impruneta, for example). Glazed pots, which are usually fired at higher temperatures, tend to withstand freezing better than terra-cotta.
To protect planted terra-cotta and glazed containers left outdoors, wrap the sides of the pots with layers of bubble wrap or burlap covered with plastic wrap to prevent them from absorbing additional moisture once the plants go dormant and their water requirements are minimal. (Wrap pots containing evergreen plants in plastic after the first hard frost.) If you have empty concrete, cement, or clay containers that are too large to move, clean them as much as possible and cover them with lids or plastic sheeting to prevent water from collecting inside, freezing, and cracking the pots. Sturdy plastic and fiberglass pots are ideal for leaving outdoors, although some plastic pots may crack if the soil inside expands as it freezes. Wooden containers made of durable hardwoods are also suitable and will age gracefully over time.
Preparing Plants for Winter
Many plants prepare themselves for winter by taking cues from the environment: As days shorten and temperatures drop, many temperate plants enter the first phase of dormancy by slowing growth. To help prepare your plants for winter, stop fertilizing them by midsummer to reduce tender new growth that is vulnerable to frost, but do continue watering regularly through fall. Evergreens, especially broad-leaved evergreens, which are particularly vulnerable to desiccating winter winds, should be watered well until the first hard frost.
In fall, when nights begin to get chilly, take cuttings of tender perennials like coleus, impatiens, and geraniums to overwinter indoors. Before the first frost, move pots of annuals, tender perennials, and tropicals indoors into a bright window. Move half-hardy perennials to a cool garage or basement, where they will drop their leaves and go dormant. Cut hardy perennials that will remain outdoors back to four to five inches above the soil line once their leaves drop after the first hard frost.
Many perennials, trees, and shrubs must have a dormancy or chill period if they are to flower and fruit the following season, and cannot be moved into the house. Leave these plants outdoors and protect them using some of the techniques described in the next section. In regions with freezing winter temperatures, move them before the first hard frost to a location such an unheated garage or basement that remains about 30 to 40° F. (Although the plants will be dormant, they will benefit from some light). Reduce watering to about once a month or when soil becomes very dry; do not allow the soil to become completely dry. Plants kept in cool indoor locations tend to break dormancy earlier in the season than their outdoor counterparts; however, they should be hardened off and moved outdoors only after the danger of frost has passed.
Woody plants that must remain outdoors have a few special requirements. To prevent the branches of deciduous trees and shrubs from whipping around and breaking in winter, loosely tie branches together after the leaves have dropped. Evergreen woody plants, particularly vulnerable to desiccating winds, can be sprayed with an antidesiccant, also known as antitranspirant, and may need to be protected against harsh winter sun with burlap screens.
Winter Protection Techniques
When left outdoors, perennials, trees, and shrubs are not only subject to extreme cold and wind, but are also vulnerable to cycles of freezing and thawing that can cause heaving (plants are literally heaved out of the soil as it expands and contracts). To reduce heaving and root damage, try to re-create the naturally insulating effects of the earth. If possible, find an area in the garden that you can dig up, and sink the pots into the ground so their roots will be insulated by the surrounding soil; then mulch heavily with straw, shredded bark, or leaves as you would other plants. If this is not possible, heavily mulching container-grown plants with straw, leaves, hay, or shredded bark will provide significant protection. Some gardeners take the extra precaution of wrapping the sides of the container with several layers of bubble wrap (to protect both delicate containers and root systems), and then mulching.
When convenient, cluster planters in a more sheltered location, such as under an eave, next to your house, or near a south-facing wall, and then mulch. Transfer small containers into a cold frame packed with sand or straw. (To create a temporary cold frame, arrange bales of hay to form four walls and top them with an old window, heavy-duty clear plastic, or a plexiglass lid.)
In open, windy areas, creating a burlap screen or windbreak provides additional protection, particularly for woody plants and shrubby perennials. Young trees and evergreen woodies, like boxwoods, which are susceptible to sunscald, will especially benefit from a burlap screen. To create a screen, pound several stakes around the plant’s perimeter, and staple three-foot-wide burlap to the stakes, forming a fence around the plant. Alternatively, create a tall cage of chicken wire around the planter, and fill this with leaves or hay to provide insulation. Group smaller plants together before surrounding them with burlap or chicken wire.
The most extreme method, and one that is recommended for half-hardy plants like fuchsias and figs grown outside of their hardiness ranges, is trenching. This requires enough garden space to dig a 14- to 16-inch-deep trench, in which the plant—pot and all—can be laid down on its side and lightly re-covered with soil. The plant’s branches and stems are covered with loose mulch and held in place with burlap for the season.
Regardless of which method you use, at the first signs of growth in spring, remove the heavy dressings from every planting and—if you protected them properly—you’ll find them rejuvenated by their winter slumber.
Shila Patel is the garden editor at marthastewart.com and the former managing editor of National Gardening magazine.
Overwintering Pretty Potted Perennials and Shrubs
In recent years growing perennials and shrubs in pots, plants previously reserved mainly for in-ground plantings, has become increasingly popular. I really enjoy the added options and interesting mixes you get by using perennials and shrubs in this manner. While many people treat perennials and shrubs planted in containers as annuals, discarding them at the end of the season, there are people who would like to overwinter these plants for use again the next year.
First, let me say there is nothing wrong with growing perennials or shrubs in pots and then discarding them at the end of the season. After all, many plants that we grow as annuals in colder climates are perennials in warm winter climates, for instance marguerite daisies. They are perennial in southern California but certainly an annual for me here in the Midwest. We think nothing of growing these “annuals” for one season, discarding them into the compost pile and then buying them new again next year. There is no reason perennials cannot be treated the same. If you garden in a small space and get easily bored, something I know happens to me, even though you can, you may not want to keep a perennial or shrub for next year. Go ahead and start over. As much as we hear about the “rules” of gardening, what is really important is that you enjoy your garden.
Pardon My Pink’ Bee Balm Monarda
Choosing the Best Plants for Overwintering
For those of you that do want to overwinter a perennial or shrub in a pot, it can be done. The easiest way to overwinter a plant in a pot is to choose one that will be hardy in the pot. The rule of thumb for a plant to be winter hardy in a pot sitting on your patio is that it should be two zones hardier than the climate zone you live in. I live in zone 5, to be certain a plant in a pot is hardy for me I should choose one that is hardy to zone 3.
The reason a plant in a pot needs to be hardier than one planted in the ground is that the soil in the pot will freeze harder than the ground. The soil will also thaw out quicker than the ground. This will lead to multiple freeze/thaw cycles throughout the winter. Freeze/thaw action is especially hard on plants. Plants in the ground benefit from the sheer mass of the surrounding land, the ground simply stays warmer than your pot will. If you are a gambler you can try to overwinter a plant that is one zone hardier than your zone (for a zone 5 garden this would be a plant hardy in zone 4) in a pot that is left sitting out. Some winters you are likely to be successful, others the plant won’t survive. If you want to try to ensure your success choose a plant 2 zones hardier. ‘
Choosing a Container
If you know you are going to leave your pot sitting outside all winter you should choose a container that won’t break from the freeze/thaw action. Clay, glazed and porcelain pots are susceptible to breaking in the winter. Although I have, at times, successfully left pots of this type out all winter, I knew I was risking breaking the pot. Good choices for a container that is going to be left outside include plastic, composite, metal and wood pots.
Little Quick Fire® Hydrangea
A perennial or shrub in a pot isn’t completely care free even in the winter. Do not fertilize your plants while they are dormant. Once they stop actively growing in the fall, stop fertilizing but still water when the soil is dry. Do not begin fertilizing in the spring until active growth has resumed. Throughout the winter your plant is still going to need some water. If the soil gets completely dry, the plant can die of desiccation. While regular watering isn’t necessary, monitor the moisture level and water if the soil is dry. Do not keep the soil soggy, as drowning your plant is also a real concern. I tend to err on the side of too dry rather than too wet. Make sure you place the pot in a location where it can drain, use pot feet or some other material to raise the pot off the ground to help with drainage.
Overwintering Marginally Hardy Plants
If you do have a plant that is hardy to your zone or only one zone hardier (a zone 4 or 5 plant in my zone 5 climate) – and you don’t want to gamble – you can still successfully overwinter these plants in pots. You will simply have to do more than leave the pot sitting on the patio. The first option is to place the pot in an unheated garage (or other unheated but protected spot). The protection from the building will be enough to keep the pot from freezing too hard and to protect it from freeze/thaw cycles. Wait as long as you can without risking the plant before placing it inside. This unheated space can either be dark or have some light. You will still need to make sure that the soil doesn’t dry out completely.
Dolce® ‘Spearmint’ – Coral Bells – Heuchera
Another option, rather than using an unheated garage is to dig a hole in an empty or out of the way spot in your garden. Place the pot (with the plant in it) into the hole. Make sure the lip of the pot is either slightly above the ground or even with the ground. Place the soil around the pot so it is secure. Since the pot is buried it will remain the same temperature as the surrounding soil. While you probably won’t need to water this plant you should check it occasionally as it may need some supplemental water. In the spring pull the planted container out of the ground, clean it up and place it back in its normal spot. Once the plant starts actively growing begin fertilizing.
Option three is to wait until fall and then transplant the plant into the soil. Leave it there through the winter and then dig it up in spring and put it back in the pot, or leave it permanently in its new home.
Sweet Romance® – Lavender – Lavandula
The final option is a technique that northern gardeners who grow hybrid tea roses know well. In very cold climates the only way to overwinter hybrid tea roses is to dig a trench, tip the plant over into the trench and then cover it with soil or mulch to protect it for the winter. This method will also work with potted perennials and shrubs. In the spring simply uncover the plant, sit the pot upright, clean it up as necessary and move it to its normal spot. Once the plant starts actively growing begin fertilizing.
Crib Sheet for Overwintering Perennials and Shrubs in Containers:
1. In order to overwinter a perennial or shrub in a container outside, it needs to be two zones hardier than the zone you live in.
2. Perennials and shrubs that are in your zone or one colder can be overwintered in an unheated garage, buried in the ground, or transplanted.
3. Perennials and shrubs in containers will need water through the winter but should not be kept wet.
4. Do not fertilize through the winter. When active growth begins in the spring, start fertilizing the plant.
Jazz Hands® Mini – Chinese fringe-flower – Loropetalum chinense
View our Pinterest board of perfectly-sized shrubs for containers here. And pin perennials for containers from this board.
Ask a Question or Give Feedback about this article. 589 Readers Rated This: 12345 (3.2)
Protecting Potted Plants over Winter
Q. Hi Mike: I have two “Pia” hydrangeas planted in clay pots that I would like to keep in their pots. What should I do to winter them over? I live in a townhouse, don’t have a garage, and have very limited garden space in the front of the house. Can I wrap the outer part of the pot to keep it from freezing and just keep the pots in front of the house? And would I need to water them or just let them go completely dormant? Thanks in advance,
- —Isabel; near Washington, DC
Mike: a friend gave me a hydrangea clipping from her garden. It has been growing well in an earthenware pot, and is now about 12″ high. Whenis a safe time to plant it? What, if any, soil preparation do you recommend?What kind of fertilizer do I use? Thanks!
- —Louise; Pottstown, PA
What is the best place to over-winter perennials in pots? I have Black-eyedSusan,
iris, lily of the valley, lambs ears, bee balm, etc. Thanks
- —Audrey, Bethlehem PA
Hi: I enjoyed your recent “will my herbs survive the winter” Question of the Week. Unlike the suburban listener who asked that question,I garden in the middle of the city with most of my herbs in terra cotta pots. What do I have to do to keep them safe through the winter? They are not fancy varieties, and may be fairly hardy—but I was wondering if the terracotta pots will crack or anything? Thanks!
- —Kate in Philadelphia
A. Excellent timing ladies! Thanks to you se, we’re going to save a lot of plants—and pots—this winter.
First, it is EXTREMELY likely that pots made of terra cotta, clay or any other heavy, stone-like material will indeed shatter if left outside over winter. When the soil inside freezes and thaws, it cracks the poor pots wide open. I’ve even lost EMPTY pots left outside during really severe winters. So lesson #1: Don’t leave stoneware containers outside overwinter if you’re gonna get all whiney when they break.
Second, there is a strong possibility that plants left outside in any kind of pot in areas where the temperature drops below freezing will die.Pots simply don’t provide the kind of protective insulation for those roots that being buried in the soil does. And you ladies can’t use the trickI detailed last week—bringing peppers, impatiens and other tropical plants indoors to provide color in your home over the winter—because the plants named in this week’s questions require a certain number of hours of winter chilling to flower correctly, OK?
Now—here are your four basic potted perennial plant options for winter.
1) Plant the plants. Even if you intend to dig them up again in the Spring, these kinds of perennials do best when their roots are tucked into good old garden soil over the winter. (And now through fall is the perfect time to plant!) Just take them out of their pots and put them in the ground anywhere you can find that drains well. If there’s absolutely NO room at your place, ask a friend or relative if you can plant them at their house for the winter. Plant at the same depth they were in their pots, and water them well. Water once a week from now till frost if we don’t get any rain,and again if we go a month or more without moisture over winter.
2) Plant the pots. Again, not if they’re terra cotta. But plastic pots can be ‘planted’ right in the ground. This may seem foolish, but it actually provides all the benefits of in-ground insulation without any risk of transplant shock—and it protects the plants’ roots from underground winter gnawing by voles. Just bury the pots, water as directed above and dig them out again in the Spring.
3) Gather all your pots together, place them against the North or east facing side of your home and cover them a good foot deep in shredded (NOT ‘whole’!) leaves after the trees give up their previous “Fall Gold”. Tobe safe, I’d remove plants from terra cotta pots and lay the plants down on the ground sideways with as much soil still attached to their root sas possible. (Leave plants inside plastic pots for that little extra vole—and rabbit and mousey—protection.) Dig them out of there as soon as the weather warms up in Spring and put them back out where you want them. You don’t have to wait until after the last frost—they can take a chill, just not a really deep freeze.
4) Take the pots into a cool, dark place that will remain between 40and 50 degrees and allow them to go dormant. Water them once when you put them down and then leave them alone till Spring, when you will take them back outside as soon as the weather warms. Water them well right away,and until we get rain.
Oh and that new hydrangea wants to be planted right now (almost EVERYTHING likes to be planted in the Fall!) in full sun to part shade in a very rich soil. So put lots of compost in the hole—which is also the plant food part of the equation: Compost!A whole bunch now and then a fresh inch a year on top of the soil. No plant enjoys chemical fertilizers, but hydrangeas like them least of all.
So do NOT use chemical fertilizers! I will know if you do, and I will send Robby the Organic Robot after you.
You Bet Your Garden Question of the Week ©2005Mike McGrath
Perennials and containers make a great gardening combination, but they will quickly go to pot if overlooked in the winter.
Plant roots are vulnerable to freezing in containers, where the soil hardens more than it would in the ground. Stems and branches — particularly those on small trees and shrubs — need protection from the deep chill as well as from snow and icy buildups. Containers should be cared for to prevent splintering and crumbling.
“The most important thing you can do when overwintering container plants is ensure that they’re vigorous and established,” said Leonard Perry, an extension horticulturist with the University of Vermont.
“Young plants that you just pop into a pot and haven’t rooted yet may not do so well,” Perry said. “The healthier they are going in, the better their chances.”
Perennials should survive long periods of extreme cold if given pre-season care. That includes:
— Feeding. Slow-release fertilizers applied before the first killing frosts arrive boost plant hardiness. Feeding should end once the plants go dormant. “With good fertility, you don’t have as many overwintering problems,” Perry said.
— Watering. Soils must be moist when the perennials are stored to help protect the roots.
— Pruning. Trim and dispose of all foliage after the plants go completely dormant. That keeps slugs and other insects from laying eggs in the residue, according to a “Simple Sensible Solutions” brochure from Walters Gardens Inc. at Zeeland, Mich.
— Trenching. Bury pots — plants and all — for improved insulation. Add a layer of mulch. Unearth and return them to their usual sites the following spring.
— Covering. Anything from evergreen boughs to blankets, straw to shredded bark can be used to safeguard pots and their contents. Securing a piece of bubble wrap or burlap around the pots also helps. Be quick to remove them once the weather warms.
— Storing indoors. Move potted plants into an unheated garage, basement, greenhouse, cold frame or similar site that matches their hardiness zone. Make sure it’s a place where the temperature stays above freezing.
Protecting the containers can pay off with additional seasons of service. “I raise my container plants off the ground in winter so they don’t freeze to the surface,” said Peter Cilio, creative director for Campania International, a designer and manufacturer of cast-stone garden accessories in Pennsburg, Pa.
“Some of the containers have feet for that purpose, or you can use pieces of wood,” he said. “A little height lets water escape through the drain holes and keeps the containers from splitting or cracking in freeze-thaw cycles.”
Large pots seem to last longer, Cilio said. More soil means better insulation. “Smaller pots constrict plant roots, hindering drainage.”
Choose your perennials well, especially for proven longevity in northerly climates. Potted perennials that are tough enough to endure at least a couple of hardiness zones colder than where you live are likely to survive extended exposure. That would mean using, say, Zone 4 plants in Zone 6.
Get more real estate in your inbox Get more stories about owning, renting, and just getting by in Toronto and beyond with our Real Estate email newsletter. Sign Up Now
And don’t forget rodent control. Mice like to cosy up to container plants in cold weather, especially those that include grasses.
“Begin baiting for mice about a month before covering your perennials,” the Walters Gardens horticulturists write. “This will help reduce their populations going into winter.”
10 colourful winter pots
Colourful winter pot displays are worth their weight in gold during the colder months, when beds and borders are looking a tad bare.
Flowers, fruit, evergreen foliage, winter plants and colourful stems all have their part to play, lifting the spirits on even the darkest of days.
More pot and container inspiration:
- Spring container displays
- Summer container displays
- Autumn container displays
- Plants for winter containers
Discover 10 great ideas for low-maintenance winter pots, below.
Cornus, carex and sedum
This zingy, low-maintenance display adds a ray of sunshine all through winter, with swaying grasses and bold uprights. Extend the display into spring by underplanting pansies with dwarf narcissi or other bulbs.
We used: Anemanthele lessoniana, Carex oshimensis ‘Evergold’, Cornus sericea ‘Flaviramea’, Sedum ‘Gold Mound’ and Viola ‘Sorbet Yellow Delight’.
Ophiopogon and cornus
This scheme combines the glossy, evergreen foliage of black mondo, Ophiopogon planiscapus ‘Nigrescens’ with the pale greens of the cornus and winter heather.
We used: Ophiopogon planiscapus ‘Nigrescens’, Cornus sericea ‘Flaviramea’ and Erica carnea ‘Aurea’.
Ideal in a sunny corner, on a wide gatepost or doorstep, this mix of hardy houseleeks adds an exotic touch. Top-dress with gravel to raise the leaves off the damp compost and prevent crown rot. Here’s how to propagate houseleeks.
We used: Sempervivum ‘Lilac Time’, Sempervivum tectorum, Sempervivum tectorum ‘Robustum’, Sempervivum ‘Rubin’, Sempervivum ‘Orange Glow’ and Sempervivum calcareum ‘Sir William Lawrence’.
This aged wooden trough has been upcycled and given a new lease of life. It’s planted up with a range of perennials and small shrubs providing flowers, scent, seedheads, berries and more. Discover more upcycled container ideas.
We used: Skimmia japonica ‘Rubella’, Gaultheria procumbens, Bergenia cordifolia, Erica carnea ‘Springwood White’, Viburnum tinus, Euonymus fortunei and eryngium seedheads.
Festuca, santolina, gautheria and ivy
Whatever the temperature, these elegant ice maidens make an eye-catching display. Replace the white-berried gaultheria with white hyacinths in spring. Remove berries that go brown to keep it looking good.
We used: Santolina chamaecyparissus, Festuca glauca ‘Intense Blue’, white-berried Gaultheria mucronata, Hedera helix ‘Glacier’, white violas.
Cyclamen, carex and skimmia
These sumptuous carmine cyclamens pop out all the more when planted alongside a the more muted carex and skimmia. A miniature ivy allowed to tumble over helps to soften any hard edges.
We used: Cyclamen ‘Mini Gem’, Skimmia japonica ‘Thereza’, Carex oshimensis ‘Evergold’, miniature ivy.
Kale, sage, rosemary and Chilean guava
The Chilean guava likes acid soil, so keep it in a pot of ericaceous compost and sink into the larger container. Keep these edibles near the kitchen door. Protect the Chilean guava from frost in a sheltered spot, porch or cool greenhouse.
We used: kale ‘Redbor’, Chilean guava (Ugni molinae), rosemary, purple sage.
Hellebore and ivy
For this container you’ll need winter-flowering hellebores, such as Helleborus x ericsmithii, Helleborus niger or Helleborus x sahinii. We’ve combined it with a variegated holly to complement the white flowers.
We used: Helleborus niger and Ilex aquifolium ‘Silver Queen’.
Nandina, heuchera and berberis
This richly coloured display provides a warm welcome on a doorstep. In spring, compost the violas and replant the rest in your borders. Here’s our step-by-step guide on how to plant up this container.
We used: Berberis x media ‘Red Jewel’, Nandina domestica ‘Fire Power’, Saxifraga ‘Blackberry and Apple Pie’, Heuchera ‘Midnight Rose’, Viola ‘Red Blotch’.
Heather, cyclamen and euphorbia
This container is packed with warm, burnished tones – perfect for midwinter colour. On sunny days, the heather might even lure in some bees taking advantage of the warmth.
We used: Carex comans, Cyclamen coum, Euphorbia amygdaloides ‘Purpurea’ and Erica ‘Mary Helen’.
As with all these containers, once the plants have outgrown their allotted space or are past their best, you can move them to a bigger container or plant them in the garden in the spring.
Winter veg and herbs for containers
- Pak choi
Should I water pots over winter?
Watering requirements vary from plant to plant, but there are some general rules to watering pots in winter. Garden plants, although stored in a cool, frost-free place are either stored dry or slightly moist to stop the roots from drying out. Keep watering house and conservatory plants, but reduce the amount of water as growth slows down in winter.
Those of us who use potted plants in our gardens, on our patios, and around our landscapes face a problem each winter: how to protect them during the long cold winter. It’s hard enough in areas where extreme cold is frequent to keep perennials in the ground alive. It’s much harder overwintering potted plants. The bulk of soil that is in the ground tends to moderate the temperatures. The small amount in pots tend to give up heat more readily. What to do?
The general rule of keeping plants in pots two zones different than the zone you live in helps. In other words, if you live in zone 6, make sure the plants you have in containers are rated to zone 4. This of course makes it difficult if you live in zone 4. There are other things you can do to carry over plants in winter. Here are some suggestions. The basic rules are, of course, to keep the soil in the pots from freezing solid and becoming totally dry; not an easy proposition.
SUPPORTS 500 LBS!
Growing in containers is easy with the right equipment. At Planet Natural we have the gardening supplies you need — pots, soils and tools — to be successful. Now, let’s grow!
First check your pots. Make sure there’s no place for water to collect on the soil surface where it can freeze and thaw and freeze again. This is particularly damaging to perennials. Good drainage is important and fluffy soil also adds a measure of insulation.
Best is to move them indoors wherever there is room. This could mean a garage, a basement or a greenhouse if you have one. An unheated garage will moderate outdoor temperatures and give your plants a good chance at survival. Covering them with tarps after insulating them with rolled newspaper or cardboard may give you the two or three degree warmth that might mean the difference between survival and freezing. Basements, if heated, pose another problem. They might be too warm. That’s fine if you’re overwintering geraniums or another plant that will continue to thrive in their pots over the cold season (don’t forget to make sure your plants have adequate light). But some might be fooled into thinking its spring and be “shocked” when replanted outside.
No room inside? Or are your pots too big to move easily? Consider sticking the plants in the ground. Again, ground temperature fluctuations tend to moderate. Containers — even the largest — tend to be more susceptible to freezing. Digging your plants up from their containers in the fall after trimming back their top growth and burying them deeply — with several inches of mulch and soil over the top — will increase their chances of survival. Smaller pots can be buried in larger pots. We knew one gardener who placed his trimmed-back potted plants in a trench, pot and all, come fall. This seemed extreme to us, especially when we helped dig them up in the spring. Needless to say, at least one pot was broken in the process and the whole operation seemed more trouble than it was worth.
Protecting trees, shrubs, and other woody potted plants that don’t take to trimming back requires extra care. Wrap delicate trunks with burlap starting at the soil line and continuing as high up as possible. Heaping leaves and mulch around these pots, using chicken wire or other fencing to hold it up and around the pot will also significantly increase survival chances.
Like real estate, location can be crucial to the success of overwintering your potted plants. Placing them against a south-facing wall or near the side of the house may give them just the temperature advantage they need. Covering them with leaves, mulch, plastic, or some other insulator will help. Another trick is to bunch your pots together and then surround them with a chicken wire cage, leaving plenty of room for leaves or other insulators. Surrounding pots with hay bales and using leaves to top them off is also effective, maybe with an old window pane as a cover.
No matter how you overwinter your potted plants, don’t just abandon them. Take the opportunity during any warm snap to uncover and inspect them. If they’re too warm and too moist allow them to dry out a bit before recovering for the night. You can expect some loss anytime you’re trying to keep plants alive over the winter. But if you provide bulk, available warmth, and/or insulation you can keep those losses to a minimum. But don’t wait until November to do it. Prepare them now so you won’t be caught by a sudden cold snap that might make your efforts useless to begin with.
What potted plants do you have to overwinter and what preparations do you take? Share your techniques with us, please. This is a difficult problem, especially for gardeners in the coldest areas. The smarter the gardener, the better the garden. So put some ideas in our heads.
When I first started gardening, I was a home renter and was very protective of my babies, (I mean plants) and therefore always kept them in pots so they could go with me whenever I moved. I was the ultimate patio garden gardener, and through the years (and multiple moves), some of my plants were adopted by my mother and friends as they became too large to travel any distance.
However, I’ve kept a few choice favorites that have been repotted a few times, been dumped in moves, and dug up by dogs, but they keep coming back and so I’m careful to make sure they are well protected each winter.
Living in an arid, warmer planting zone, I have perfected what works well for my particular situation. But there are varied ways to keep your outdoor potted plants safe from freeze in almost any condition, and I will explain those below.
Table of Contents
WHERE YOU NEED TO PROTECT YOUR POTTED PLANTS
Before we begin, it’s important to realize that any perennial you have potted will be less hardy within a pot. Depending on the zone you live in, you will want to make sure your plants are hardy to at last one (if not two) zones colder than where you are. Plants are zoned by on the assumption that they will be on the ground where it doesn’t receive that same conditions through the winter as potted plants. Potted plants have the added disadvantage in that they begin to freeze from the sides, and not only the surface of the soil, which can compromise the root system pretty quickly. Despite this, if your zone drops below freezing and stays there for any length of time, then you will want to make sure your plants are well protected from the elements.
As described in my previous article addressing this very issue, there are a variety of ways to take care of any sort of potted plant you may have, including bringing them indoors, for the winter. But hardy potted perennials often need a period of cold dormancy for their own health to rest and regenerate and should be left outdoors for the winter with proper protection.
ZONAL WINTER PROTECTION
Depending on where you live, you’ll want to approach your overwintering protection techniques with weather in mind. Northern climates will obviously need more protection than those located in the South. I break it down here with techniques you can use for each zone and then detail below what I use in my zone (zone 7) where we can have a week or two of single digits each winter, and a series of freezes followed by a thaw.
Don’t begin to insulate your pots until temperatures are dipping steadily below freezing and staying there through the nights. A good rule of thumb is to not begin insulating your pots until you have had at least three good freezes.
I don’t recommend ever trying to overwinter your plants in pots in zones 1-3 at all. If you have potted plants and want to try and get them to survive through the winter, your only real alternative is to bring them indoors, or into a cellar or basement where temperatures will stay cool or a semi-winter dormancy. You might have some success with burying your pots and adding a thick layer of mulch to it, especially if it is a very hardy and cold tolerant
You have a few options for overwintering in zones 4-8, the most successful being that you bury your pots so at least 80% of the pot is below ground each winter. This helps to mimic the natural protection it would receive if it was planted in the ground, and if you place a good layer of mulch over the top you are pretty much guaranteed that your plant to come back to life the following spring. However, this technique can be best left to the colder zones, such as 4, and possibly 5 as easier, and more popular methods are available for the warmer zones.
Another technique is to make sure that your plant is in a larger pot that what you think you need to provide the extra insulation it needs to keep the roots from freezing from the sides. Having used this technique many time with perennial strawberries and herbs in a zone 4 where temps regularly dipped into the -20s and 30s I can vouch for it’s effectiveness.
Another way you can protect your plants is by providing a layer of pot insulation as I will describe in further detail below.
Despite the facts that temperatures may drop below freezing regularly in zones 8 and higher, they rarely stay there for any length of time, and certainly not long enough to cause a hard ground freeze – meaning that it is doubtful that your plant roots will ever been in any danger of freezing to death. If you want to error on the side of caution, you can certainly try one of the above mentioned techniques, but since I have unwittingly overwintered plants in a zone 7 with no protection, I imagine you would be fine just leaving them alone.
WHAT YOU NEED TO OVERWINTER YOUR POTS
If you aren’t going to bury your pot, or are unsure if your pot is significantly larger than your rooting system, you’ll want to insulate your pot using one of the following descriptions. At the very least you’ll need:
- Burlap – I prefer rolls of narrow burlap because it’s easy to wrap around larger pots.
- Plastic Wrap (alternative: used plastic grocery bags)
- Heavy duty paper stapler
OPTIONAL ALTERNATIVES FOR ADDED PROTECTION IN COLDER ZONES:
- Bubble wrap roll or Insulation
- Packing tape ( or duct tape)
If you can, move your plants to a sheltered area, and group together to provide additional winter protection. Sunny, south facing walls are also a good location to consider. Providing a layer of mulch over the top of your pot is also a good idea once your plant has gone completely dormant. And if you have ceramic, concrete or clay pots, you may want to consider putting a weighed down sheet of plastic over the top to keep the soils from absorbing additional moisture and then freezing and expanding – which could crack the pot materials (I actually had this happen: it was so depressing).
STEP 1: LAYER IN PLASTIC
Despite living in a zone 7, it has always dropped into the single digits each winter and stayed there for a few weeks at a time in the past. I also am always wary of hard freezes followed by a thaw before freezing again; to me this indicates the perfect weather to wreck havoc on my potted perennials.
Because of this, I use a double layered insulation technique using a garbage bag, or my old plastic shopping bags (you can buy sheets of plastic, but why bother if you have a billion bags you can recycle?). And if you live in a cooler zone, you can even use rolled housing insulation or bubble wrap (consider lining it inside your pot walls as well before you even plant for a TRIPLE layer!) for further protection.
*You might also like: DIY Potting Table From an Old Wine Rack
Simply drop your pot into the bag and wrap it around before securing it with packaging or duct tape. If your pot is too heavy (as most of mine are), then wrap it around the pot- providing at least two to three layers of plastic insulation.
Helpful hint: Make sure the tape isn’t gapped so water can get in between the pot and layers of insulation. This may freeze and damage your pot. Also, I daisy chain my plastic bags together so all I have to do is wrap them around and secure with tape.
STEP 2: WRAP IN BURLAP
Once your plastic is secure, wrap the pot in burlap using at least two layers, and staple the ends shut. The burlap is breathable enough that through the winter weather it will dry out and avoid mildewing, but is made of jute plant fibers (also known as sisal) and provides excellent garden insulation.
Helpful hint: Wrap your burlap as tightly as possible to avoid it pulling away from the pot due to snow and ice accumulation if you live in an area of high winter precipitation.
STEP 3: MULCH
I think it is equally important to remember that the soil surface will be the first to begin to freeze during the winter months. Although most roots are deep enough not to be affected by a top-down freeze, it never hurts to error on the side of caution once the temperatures are steadily below freezing. You don’t need much mulch to make a difference, and generally, a two-inch layer is the perfect amount to offset any top-down damage. Just be sure to pull it back from your stems once spring arrives to allow the soils beneath to further warm for new growth, and to avoid holding moisture near the plant base. This can cause unnecessary rot or mildew.
Water your plant well (but do not soak) before adding a layer of mulch. This will help provide moisture to the roots through the colder months.
TIME TO WRAP!
As seen above this isn’t a very complicated or time-consuming process, and it is so worth the little effort it takes to secure your outdoor potted plants for the winter. First and foremost keep in mind the zone you live in, and how your plants weather each winter. You know your plants and yard’s micro-climate the best!
If you choose to wrap your plants over burying them, or providing larger pots, always be sure to not start wrapping until they have reached dormancy, and you know winter has set in to keep from overheating your plants. Three good freezes usually indicate that winter is trying to arrive, and you need to start taking providing some form of protection.
If you have any techniques you’d like to share or found the above article helpful, please let us know below! And as always share with your friends and family so they can keep their plants through the winter months!