# When Cold Frames Really Help

- Link: https://lifeandwork.blog/when-cold-frames-really-help/
- Published: 2026-07-05T21:47:49-05:00
- Author: Bert Swope

Many gardeners plant cool-season vegetables like spinach, kale and winter lettuces
in cold frames during the fall season to protect half-hardy perennials and overwinter
bulbs safely.

Cold frames feature sloping sides fitted with transparent roofs that slant to capture
winter sun’s warming rays, often made out of wood frames or using concrete blocks
as insulation for extra insulation value.

## They Keep Seedlings Healthy

Cold frames offer you a fantastic way to grow plants earlier and later in the season
than would otherwise be possible. As they create an environment about 1.5 zones 
warmer than its surroundings, it makes cold frames ideal for sowing seeds that require
additional warmth to germinate or holding on crops until temperatures warm up further.

Cold frames not only warm the soil and air, but they also protect tender plants 
from frost and garden pests. A cold frame can also be used to overwinter hardy salad
greens like winter lettuce and mizuna as well as start seeds of cold-resistant herbs
such as parsley, cilantro and chives.

Build a basic cold frame by covering an open ground area 3-by-6-feet in size with
sturdy wood or brick structures and then adding a clear lid made from transparent
material like glass (such as an upcycled window sash), acrylic sheet or plastic 
sheet – hinges may come in handy here as they allow opening up on warm days to provide
ventilation; some people even choose to paint the interior white to reflect more
light!

When in use, the lid must be opened gradually for longer on sunny days to prevent
overheating and monitor the temperature with an attached thermometer. Ventilation
is essential as moisture generated from water evaporating into the frame can quickly
kill plants if left alone.

Once this has been accomplished, the gardener closes the lid of their cold frame
to retain heat and safeguard their crop from frost. A cold frame makes it possible
to start planting outdoor vegetables and flowers as early as mid-May in many locations,
and is also an invaluable way to “harden off” seedlings and transplants grown indoors
or at garden centers prior to being moved outside for long enough periods each day
to adjust them to outdoor conditions – an often challenging process when done manually.

## They Keep Leafy Greens Growing

Leafy greens thrive in cold frames, providing fresh salads throughout winter and
providing much-needed vitamins when other crops have long since gone to seed. Lettuce,
kale and spinach thrive well as do radishes and green onions; even hardier varieties
like mizuna and winter purslane may survive; though their seeds must be regularly
reseeded to keep up their production.

Before transplants can be placed outdoors permanently, most need a period of acclimatization
known as hardening off to outdoor conditions – or “hardening off”. This process 
involves gradually placing plants outside for longer periods each day over several
weeks or two and shutting them back indoors at night to protect from frost damage.
Cold frames make hardening off easier as you simply open their lid gradually more
often each day to gradually expose crops to cooler temperatures until they have 
fully adjusted to the weather conditions.

Cold frames can also be useful for starting warm-season vegetable seeds and rooting
woody cuttings from shrubs and perennials, such as roses or lilacs. A similar structure
known as a hot bed can give warm-season veggie plants like tomatoes and peppers 
an early headstart while rooting woody cuttings from roses and lilacs.

To build a cold frame, select an area that gets full sun throughout the day – ideally
southern exposure – and construct a rectangular frame, commonly 3 by 6 feet, so 
rain or snow runs off easily. Use hinges to attach a clear cover that can be opened
for ventilation on warmer days; fill your frame with nutrient-rich, well-draining
soil amended with compost for increased drainage; add mulch or straw as extra insulation
against temperature extremes (some temperatures can exceed 85F in mild winter days),
using a thermometer to monitor temperatures inside and adjust sash accordingly to
reduce fluctuations between these extremes.

## They Keep Root Crops Growing

Add an extra zone of warmth to your garden for maximum planting success, harvesting
crops well beyond peak gardening season and even protecting delicate vegetables 
from frost or pests, according to Eliot Coleman’s Winter Harvest Handbook. Cold 
frames also protect tender vegetation from freezing temperatures and pest infestation,
protecting it from becoming targets for attack by Eliot Coleman himself!

Root crops like carrots, beets and radishes thrive in cold frames as do leafy greens
such as spinach – one of the fastest-growing varieties! But you could also experiment
with growing lettuce, kale collards turnips or other hardy varieties within your
cold frame.

As with any greenhouse, cold frames require careful management in order to avoid
overheating and damaging plants. Furthermore, water should be applied sparingly 
during cooler weather as evaporation occurs more slowly.

Visit your local library for resources on building and using cold frames, such as
The Year-Round Vegetable Gardener by Niki Jabbour which contains expert advice for
making the most out of cold frames and other hoop houses.

Prefabricated cold frames available at stores provide a convenient way for even 
busy gardeners to extend their growing season, and some even feature automatic vents
which open and close depending on temperature fluctuations, to prevent overheating.

Frames can be placed atop existing soil or filled with soil for an elevated bed.
Some come equipped with built-in heating cables, making them an excellent choice
in cold climates. If you prefer DIY options, old milk jugs or soda bottles, plastic
covered tomato cages, glass and metal cloches or transparent “houses” such as old
milk jugs can add three or four weeks more growth to your garden.

## They Keep Winter Harvests Coming

Cold frames help extend harvest seasons for leafy greens and root crops by protecting
plants from frost in late autumn, enabling growers to harvest last of summer vegetables
even as temperatures decline – this can bring extra income as consumers are willing
to pay a premium price for out-of-season produce.

Cold frames offer many other advantages beyond offering extra winter harvest protection,
including helping start seeds early in spring for cool-season crops like tomatoes
and eggplants. Furthermore, cold frames can moderate soil temperatures – an advantage
when dealing with heat-loving tomatoes and eggplants – and be used to acclimate 
winter pot plants and bulbs, which often take quite some time to adapt to outdoor
temperatures.

Russ Libby shared his homemade wooden frame at the Unity Land Institute Small Farm
Field Day to demonstrate how he uses it for starting and growing winter-hardy vegetables
like spinach, kale, chard and bok choy – plus overwintering flowers such as fuchsias,
geraniums and nasturtiums in it!

Cold frames can be built onto any structure, such as a greenhouse, hoop house or
simply an insulated box. Wood construction tends to provide the best thermal barrier
and help regulate temperatures within the frame; adding insulation can further enhance
performance of this structure.

To keep crops in top condition during the winter season, Libby suggests venting 
the frame periodically to allow air circulation. For optimal results, do this during
daytime when temperatures are warm before sundown – or use automatic lid openers
which will open or close themselves depending on weather.

To maximize a cold frame’s effectiveness on your property, it is crucial that you
understand it thoroughly. Take note of areas that naturally receive more warmth –
for instance the south side of a house or fence or where snow melts first in spring–
and build there. While ready-made frames may cost less and offer greater stability
than DIY options, Libby suggests building one yourself if time and physical ability
permit. Doing it yourself saves money and guarantees quality.

### Share this:

 * [  Print ](https://lifeandwork.blog/when-cold-frames-really-help/#print?share=print)
 * [More](https://lifeandwork.blog/when-cold-frames-really-help/#)

 * [[
 * [Share on Tumblr](https://www.tumblr.com/share)
 * [  Email ](https://lifeandwork.blog/when-cold-frames-really-help/?subject=%5BShared%20Post%5D%20When%20Cold%20Frames%20Really%20Help&body=https%3A%2F%2Flifeandwork.blog%2Fwhen-cold-frames-really-help%2F&share=email)
 * [Tweet](https://twitter.com/share)
 * [  Telegram ](https://lifeandwork.blog/when-cold-frames-really-help/?share=telegram)
 * [  WhatsApp ](https://lifeandwork.blog/when-cold-frames-really-help/?share=jetpack-whatsapp)
 * [  Reddit ](https://lifeandwork.blog/when-cold-frames-really-help/?share=reddit)
 * [  Threads ](https://lifeandwork.blog/when-cold-frames-really-help/?share=threads)
 * [  Mastodon ](https://lifeandwork.blog/when-cold-frames-really-help/?share=mastodon)
 * [  Nextdoor ](https://lifeandwork.blog/when-cold-frames-really-help/?share=nextdoor)
 * [Post](https://x.com/share)
 * [  Bluesky ](https://lifeandwork.blog/when-cold-frames-really-help/?share=bluesky)

### _Related_