Cold Frames: Extend Your Growing Season Year-Round

Extend your harvest and protect your plants all year long!

Few tools in the gardener's shed are as humble yet heroic as the cold frame. Like a miniature greenhouse, these low-tech contraptions create a microclimate that can squeeze out a few more precious weeks, or even months, of garden benefits!

Whether you're protecting crops from a surprise spring freeze, pushing your fall vegetable garden a little longer, or giving your seedlings a place to harden off before they brave the great outdoors, a cold frame just might be your new best friend in the garden.

By capturing solar warmth and sheltering tender plants, cold frames shield crops from frost, wind, and sudden temperature drops. Gardeners have used these passive solar protectors for centuries, from medieval stone-walled gardens to today's raised bed wonders. Also known as a sun box, propagation frame, cloche, or grow box, these are affordable and adaptable! A cold frame helps you protect prize plants, extend harvests, and get a jump on the growing season. All with the help of mother nature herself.

Types Of Cold Frames
How To Use A Cold Frame All Year Long
Cold Frame Tips & Tricks
Extend Your Growing Season With Cold Frames!

What Is A Cold Frame?

A cold frame is a simple, ground-level enclosure with a transparent lid that traps solar heat. This passive heating creates a warmer environment than the surrounding garden, allowing you to extend your growing season or protect vulnerable plants from sudden weather swings. Similar to adding plastic row covers to your garden beds, a cold frame is a more permanent garden addition.

Typically constructed from wood or metal with a clear lid made of glass, acrylic, or polycarbonate, a cold frame can be as elegant or as makeshift as your creativity allows. Some folks even build them using a stack of hay bales with a reclaimed window on top. You can repurpose old materials or buy a pre-fab option, the result is the same: a pocket of warmth to protect your plants.

Banking soil along the outside walls or partially burying your cold frame helps retain heat. For extra heat retention, try painting the interior black to absorb sunlight during the day and slowly radiate it back overnight, just like dark rock walls in traditional European gardens.

Types Of Cold Frames

There's no one-size-fits-all when it comes to cold frames. Choose or build a version that best suits your garden goals:

Traditional Wooden Cold Frames: Built with wood and a hinged glass or plastic lid, these durable designs blend into most gardens and are easily customized.
Metal-Framed Cold Frames: Lightweight, rust-resistant, and long-lasting, they're ideal for mobility and ease of use.
Pop-Up Cold Frames: Portable and compact, these are perfect for small-space gardeners or quick season extension.
Raised Bed Cold Frames: Combine a raised bed and cold frame for dual-season power, especially helpful in colder regions.
Electric Cold Frames: With built-in heating elements, these let you garden year-round, even growing warm-season crops through winter.
Hay Bales & Reclaimed Windows: When you need a cold frame in a pinch, stack hay bales into a square and top with a salvaged window or clear sheet.

How To Use A Cold Frame All Year Long

Perfect for starting your first batch of seedlings, nurturing tender perennials, or harvesting fresh greens in the snow! Cold frames are a must-have for any garden enthusiast!

Cold frames aren't just a springtime tool either. They can serve many purposes across the seasons, expanding your gardening potential with every use.

Spring

Harden Off Seedlings: Transition your indoor seedlings to the garden using a cold frame. Gradually introduce indoor seedlings to the elements by sheltering them in a cold frame for part of the day. Start by placing them inside the closed cold frame for a few hours a day, gradually increasing light and air exposure.
Jumpstart the Season: Start early crops by planting cool-weather vegetable garden crops like lettuce, spinach, kale, and radishes weeks before the last frost. The cold frame will protect them from chilly nights and give you a head start on the season.
Warm the Soil: Heat the soil faster to sow seeds earlier and get a jump start on the growing season.
Guard Against Cold Snaps: Protect plants and seedlings from unexpected frosts and dips in temperature.

Summer

Shade Young Plants: Use a cold frame to reduce wind stress or shield transplants from harsh afternoon sun.
Protect Delicate Plants: Use your cold frame to shield young transplants from intense sun or strong winds.
Extend Harvests: Late-season crops like Bush Beans or Cucumbers can thrive in the controlled environment of a cold frame.
Quarantine: Place new plants in a protected form of isolation until you can be sure they are pest-free. Or use a cold frame to isolate a plant during treatment of an outbreak to keep the pests from spreading.

Fall

Extend the Growing Season: As temperatures drop, use your cold frame to grow hardy greens, carrots, and beets well into late autumn.
Save Tender Plants: Move Herbs or smaller potted plants into a cold frame to protect them from early frosts.

Winter

Winter Gardening: Cold frames are perfect for cool-season vegetables, hardy greens like kale, chard, and spinach, keeping them fresh even in snowy conditions. Cruciferous vegetables can be kept growing longer here, too!
Storage: Use your cold frame as a temporary shelter to store pots or trays of dormant plants. Keep seeds where they won't freeze but remain cold. Or just use your cold frame to keep tools and supplies clean, dry, and rust-free.
Root Cellar: Store dormant bulbs, edible tubers, root vegetables, and other vegetables between layers of straw, clean mulch, or sand in your cold frame. You can also cover plots of root crops while they're still growing in the ground with a portable cold frame to extend your harvest.

Cold Frame Tips & Tricks

Placement: Position your cold frame in a sunny spot with southern exposure for maximum warmth.
Ventilation: Open the lid on sunny days to prevent overheating and allow airflow.
Insulation: Add extra protection in winter by lining the sides with straw or bubble wrap.
Maintenance: Keep the panels clean to allow maximum sunlight to reach your plants.
Moisture Control: Avoid overwatering or letting condensation build up. Too much can encourage mildew and disease. Watch for soggy, wet foliage and open the lid to air out your crops when temperatures are safe.
Use the Finger Test: Before watering new plants, always check the soil moisture by using the Finger Test.
Rodent & Pest Protection: Secure the base with wire mesh or hardware cloth to deter nibblers and diggers like rabbits or voles.
Compost Pairing: Place your cold frame near or over an active compost pile. The heat from decomposition can add warmth and boost growth.

Extend Your Growing Season With Cold Frames!

Cold frames are a game-changer for gardeners! Offering endless possibilities to grow more plants, extend your harvest, and protect your garden from unpredictable weather. From salvaging a late harvest to giving your spring garden a head start, cold frames offer a simple, time-tested solution to stretch your garden's productivity. These versatile garden allies don't just extend your seasons, they expand your possibilities!

It doesn't matter if you're building one from scratch or selecting a ready-made version; the cold frame's blend of old-world wisdom and modern utility is sure to enrich your edible landscape! They're an affordable and effective way to make the most of every growing season while giving your plants the best chance to thrive.

Nature Hills Nursery has plenty of plants to help you fill your new cold frame! We're sure you'll find the perfect fit for your gardening needs. Bring your garden to life year-round with this simple yet powerful tool!

Happy Planting!

Frequently Asked Questions

How do cold frames help extend the growing season beyond the last frost?

Cold frames act as passive solar collectors, trapping heat beneath a transparent lid to create a microclimate that can run 10 to 20 degrees warmer than the surrounding garden. This buffer allows gardeners to start cool-season crops like lettuce, spinach, and kale weeks before the last frost date in spring, and keep harvesting well into fall or even early winter in many zones. To get the most out of your cold frame, orient it facing south, prop the lid open on warm sunny days to prevent overheating, and close it back up each evening to lock in the day's accumulated warmth.

How do you build a simple cold frame for your garden?

A simple cold frame can be built using four wooden boards (a common size is 3 feet wide by 6 feet long) arranged as a bottomless box, with the back wall slightly taller than the front to create a slope that angles toward the sun. Top it with a hinged old window, sheet of polycarbonate, or acrylic panel to trap solar heat and shed rain. For extra warmth, paint the interior black to absorb daytime heat and radiate it back overnight, and bank soil along the outside walls to improve insulation. Set your cold frame in a south-facing location, partially sink it into the ground if possible, and start using it in early spring or fall to extend your growing season by several weeks on either end.

What materials work best when making a cold frame at home?

Wood and metal are the most common frame materials, with untreated rot-resistant lumber like cedar being a top choice for longevity. For the lid, glass offers excellent light transmission and heat retention, while polycarbonate and acrylic are lightweight, shatter-resistant alternatives that work just as well. You can even repurpose old materials like hay bales stacked as walls with a reclaimed window laid on top. Whatever materials you choose, paint the interior black to maximize heat absorption and bank soil along the outside walls to further insulate and retain warmth.

How do you use a cold frame to protect plants through fall and winter?

As temperatures drop in fall, move tender perennials, overwintering crops like kale and spinach, or potted plants into your cold frame to shield them from frost and freezing winds. The trapped solar heat keeps the interior 10 to 20 degrees warmer than outside air, which can mean the difference between survival and loss for plants in Zones 5 through 7. On sunny winter days, prop the lid open slightly to prevent overheating and excess moisture buildup, then close it before sunset to lock in warmth overnight. Position your cold frame against a south-facing wall or fence to maximize solar gain and keep a thermometer inside so you can monitor conditions and adjust ventilation as needed.

What vegetables and herbs can you plant in a cold frame before the last frost?

Cold frames allow you to get a head start on cool-season crops like lettuce, spinach, kale, arugula, radishes, carrots, and Swiss chard weeks before your last frost date, as these plants tolerate temperatures down to the mid-20s°F when protected. Hardy herbs such as parsley, cilantro, and chervil also thrive in a cold frame during late winter and early spring. In Zones 5 through 7, you can typically begin sowing seeds inside a cold frame 6 to 8 weeks before your last expected frost, giving transplants a strong root system before they move to open garden beds. Start with a soil thermometer to confirm your cold frame soil has reached at least 40°F, then sow your first seeds and monitor ventilation on sunny days to prevent overheating.

How does a cold frame compare to a greenhouse for year-round gardening?

A cold frame functions like a miniature greenhouse by trapping solar heat under a transparent lid, but it operates passively without electricity, heating systems, or the significant cost and space a full greenhouse requires. While a greenhouse offers greater temperature control and growing capacity, a cold frame can still extend your season by several weeks on both ends, protecting crops from frost and wind with minimal investment. For most home gardeners, a cold frame is the more practical first step, and you can boost its performance by painting the interior black for heat absorption or banking soil against the outside walls for added insulation. Start by placing your cold frame in a south-facing location to maximize solar gain and get the most out of this simple but effective season-extension tool.

What plants grow best in a cold frame during spring, fall, and winter?

Cold frames excel at protecting cool-season crops like lettuce, spinach, kale, arugula, radishes, carrots, and herbs such as parsley and cilantro through spring and fall shoulder seasons. In winter, cold frames can keep hardy greens like mache, claytonia, and overwintering spinach alive in USDA Zones 5 and warmer, often with no supplemental heat required. In early spring, use your cold frame to start seeds 4 to 6 weeks ahead of your last frost date or to harden off seedlings before transplanting them into the garden. Stock your cold frame with what you love to eat, focus on cool-season varieties rated for your zone, and crack the lid on sunny days when temps climb above 40 degrees Fahrenheit to prevent overheating.

When should you start seeds in a cold frame for the best results?

Start seeds in a cold frame 4 to 6 weeks earlier than you would outdoors, timing based on your last expected frost date and your USDA hardiness zone. In zones 5 to 7, this often means beginning cool-season crops like lettuce, spinach, and kale in late February or early March. Warm-season seedlings like tomatoes and peppers can be started indoors first, then transitioned to the cold frame in early spring to harden off before transplanting. Check soil temperature with a thermometer, aiming for at least 40 to 50 degrees Fahrenheit inside the frame, and crack the lid on sunny days to prevent overheating.

How do you ventilate and manage temperature inside a cold frame?

Ventilation is critical to preventing overheating, which can stress or kill plants faster than frost. On sunny days, even in winter, interior temperatures can spike well above 40 degrees Fahrenheit warmer than outside air, so prop the lid open a few inches whenever temps climb above 45 to 50 degrees Fahrenheit inside. A simple stick or wooden block works perfectly as a prop, and you can use an automatic vent opener if you are not able to check on your cold frame daily. Monitor interior temperatures with a min-max thermometer and develop a routine of venting in the morning and closing the lid again before sunset to trap daytime warmth overnight.

How do you prepare and maintain a cold frame as seasons change?

Seasonal cold frame management centers on ventilation and insulation adjustments. In early spring, prop the lid open on sunny days when temperatures exceed 40 degrees Fahrenheit to prevent overheating and begin hardening off seedlings, then close it each evening to lock in warmth. As fall arrives, bank soil against the exterior walls and consider painting the interior black to maximize heat absorption and radiation during cooler nights. Check your frame daily, adjusting the lid based on outside temperatures and monitoring for condensation, which signals the need for more airflow.

Cold Frames: Your Year-Round Gardening Ally!