# Overwintering Perennials in a Cold Frame

- Link: https://lifeandwork.blog/overwintering-perennials-in-a-cold-frame/
- Published: 2026-09-27T16:46:28-05:00
- Author: Bert Swope

![Overwintering perennials in a cold frame from strawberries to herbs](https://i0.
wp.com/i.imgur.com/UbvNKMq.jpeg?w=790&ssl=1)

Container perennials rated one or two USDA hardiness zones colder can survive outdoor
winter conditions in pots provided they are planted in an area that remains warmer,
covered with thick mulch and regularly watered before the ground (and/or potting
mix) freezes over. To do this successfully, group pots together and water before
freezing temperatures arrive – water them just before their soil freezes!

Build a simple rectangular frame in the desired size, with its back sloped higher
than its front to help snow and water flow off easily. Fill this frame with nutritious
compost as well as additional insulation in the form of straw or mulch for best 
results.

## Strawberry Plants

Strawberry plants require protection from winter elements when growing outdoors 
or in containers, no matter whether it be gardens, raised beds or containers. June
bearing varieties that produce their fruit all at once in late summer or early fall
may be more susceptible to freezing conditions if cut back post-harvest and should
therefore remain fuller than normal for this winter period.

Everbearing strawberries, which produce throughout the year, are more resistant 
to cold temperatures but still require additional care during winter. Thawing and
freezing of their roots could prove fatal even with protective mulch around their
base.

To protect them, create a season-extending cold frame using a single-pane window
and salvaged wood boards from recycling bins. Position it with its front facing 
south to catch morning sunlight, while making the back slightly taller with sloped
top to allow rain and snow to roll off easily. This will trap warmth and sunlight
inside while helping maintain temperature regulation for your strawberry plants.

## Herbs

Cold frames provide herbs with an extended growing season in winter by trapping 
sunlight and heat to maintain above-freezing soil temperatures. A typical cold frame
consists of a wooden box covered with an old window or Plexiglas lid; its simple
structure helps extend harvest season from fall into winter.

Oregano, thyme, and mint perennials make ideal candidates for overwintering in a
cold frame, thanks to their hardy woody stems that resist frost damage. Annuals 
such as basil or dill don’t tolerate freezing temperatures as well and tend to die
off quickly in cool weather.

Many herbs require a thick layer of winter mulch to prevent their roots from freezing
and thawing repeatedly, which can cause root rot. Straw or evergreen boughs work
well as winter mulch. Containerized plants should also be protected from winter 
winds using windbreaks such as walls. Pots should also be sturdy enough to withstand
freezing temperatures.

## Vegetables

Cold frames are an inexpensive and efficient way to extend the growing season for
leafy vegetables and root crops. Use it to transition seedlings from indoor pots
into the outdoor environment gradually, or grow through winter using its microclimate.

To maintain an ideal cold frame temperature, the key is monitoring its internal 
environment and adjusting the transparent lid accordingly. On warm days, crack open
your lid slightly for cooling air to circulate while at night close your lid to 
trap its warmth inside the structure.

Container-grown perennials rated one or two USDA hardiness zones colder than your
garden area have an excellent chance of surviving through the winter in a cold frame,
provided their soil and potting mix freeze solid. Peas, spinach and chard, carrots,
radishes and beets are good candidates as these will benefit from having warmer 
soil in a cold frame that better tolerates frost than those grown directly outdoors.

## Flowers

Cold frames extend your growing season by trapping sunlight and warmth while protecting
plants from cold winds and snowfall, providing an ideal solution for cool-weather
crops like greens and root vegetables.

Perennials in containers or shrubs that fall one or two USDA hardiness zones below
your area can benefit from being placed in a cold frame. A simple wooden box or 
stacks of old windows tacked together make an effective environment, with each window’s
top section left open so as to allow sunlight and airflow through.

Plants from the nightshade family such as tomatoes, peppers, potatoes, eggplant 
and melons should not be grown alongside strawberries as they share many of the 
same diseases. Companion herbs like lemon basil (Ocimum basilicum ‘Lemon’ or cinnamon
basil, Ocimum basilicum ‘Cinnamon’) may help repel tomato hornworms, whiteflies 
and aphids that attack strawberries while borage (Borago officinalis) attracts bees
that pollinate them while borage (Borago officinalis) attracts bees that pollinate
their pollination needs according to Spoonemore’s reports. A ground cover such as
white Clover (Trifolium repens) helps suppress weeds while conserving moisture levels
insulate against heat-upkeep.

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