The Best Cold Frame Greenhouses
Updated: Feb. 13, 2023Extend the growing season with a cold frame greenhouse. It's more of a box than a house, perfect for protecting seeds and starts from cold weather.
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Buying a Cold Frame Greenhouse
Want to start your seeds early and get a jump on the growing season? There are a couple of ways to do it.
If you don’t have room for an actual greenhouse, stake out an area in your basement or garage and purchase grow lights. If you do have the space, there’s another way: Set up a cold frame greenhouse right in the garden. It uses the heat of the sun to provide an environment that’s five to 10 degrees warmer than its surroundings — similar to the growing conditions 500 miles farther south.
In general, a cold frame is a greenhouse with no heat source. While there are large walk-in ones, the most common ones are small, and many are portable. They’re essentially one or two feet tall boxes with open bottoms, clear or opaque sides and transparent lids.
You can set a cold frame directly on the ground or partially bury the sides for extra insulation. Most are built with a slight slope facing south to better catch the sun.
A cold frame is simple enough to DIY, and many people do. But if that’s not your thing, they’re easy to find. When shopping, consider the following:
- Size: Cold frames are built with little headroom to maximize warming, but footprints vary. Anything less than 4- x 8-ft. is considered portable. Larger cold frames are best left in one place.
- Lids: These are hinged to allow access to what’s inside. Some cold frames have more than one lid so you can reach some plants or germinating seeds without disturbing others.
- Frame material: Common materials include glass, wood, polycarbonate, fiberglass and aluminum. Wood, the heaviest and best-insulating material, is most suited for a stationary installation. Aluminum is generally the priciest and longest lasting. Some frames feature an aluminum structure supporting polycarbonate or glass panels.
- Lid material: Because the lid must be transparent, these are usually glass and polycarbonate. Glass weighs more and it’s stronger, so it’s better for windy conditions.
- Ventilation: Most cold frames have hinged lids that can be adjusted or removed. If the lid can’t come off, there should be vents on the sides.
Best High-End Cold Frame
The Juwel Biostar Cold Frame is made of twin-wall polycarbonate panels for excellent heat retention, with three lids that open and close independently. Twenty inches high, it features a 3- x 5-ft. footprint.
The no-drip interior coating protects plants from condensation, and the unit comes with four corner stakes to anchor it securely to the ground. It’s made in Austria, a country on the leading edge of cold frame technology, which accounts for its high price.
Best Budget Cold Frame
The Hanover Single Garden Bed Cold Frame can do everything any other cold frame can do for about one-third the cost, so it’s a great buy for first-time and experienced growers alike. With an aluminum frame and double-walled polycarbonate panels, the unit is light enough to move around the garden.
Two top panels open independently so it’s easy to access plants, and the 3- x 2-ft. space inside provides plenty of growing room. The roof has adjustable latches for ventilation.
Best Multi-Tier Cold Frame
The lean-to Outsunny Three-Tier Cold Frame stands just under five feet tall with a 2- x 4-ft. footprint. The three shelves provide plenty of space to organize your plants and even store garden tools. It’s supported from the back by another structure.
The frame is mostly aluminum with a galvanized steel base, providing strength to resist the wind. The polycarbonate panels admit 90 percent of the sun’s light, giving plants the warmth they need on cold days.
Best Wooden Cold Frame
If you’re going to DIY a cold frame, you’ll most likely make it from wood. But why bother when you can purchase the MCombo Cold Frame instead?
The three-foot-square base provides lots of growing room. The polycarbonate panels diffuse incoming light and guarantee maximum absorption without overheating.
The two top panels of triangular roof open to provide access from both sides. It’s easy to set up in the garden, on a patio or anywhere else you want to start seeds or tend seedlings.
Best Pop-Up Cold Frame
The Zenport 4- x 4-ft. Cold Frame Greenhouse comes with an easy-to assemble triangular aluminum frame, plus a vinyl top covering that rolls back for ventilation.
It’s easy to set up over an existing garden bed, providing a controlled microclimate for fragile flowers and vegetables. It lets you to cultivate plants that wouldn’t otherwise grow in your climate zone. It’s lightweight enough to move from place to place in the garden.
Best Modular Cold Frame
What happens when you run out of space in your cold frame? If you have Delta Park Gable Roof Cold Frame, you simply add another one with the brackets provided. Each module provides one square meter (39.4- x 39.4-in.) of growing space.
This cold frame features polycarbonate side and roof panels that are adjustable and removable for ventilation, with good light transmission and insulation.
Best Hoop-Style Cold Frame
The Haxnicks Mini Greenhouse provides 1.67- x 3.25-ft. of growing space, and the curved roof lets light in from every angle. A handle makes this small cold frame easy to move.
It features a black galvanized steel frame and UV-resistant clear plastic cover, with adjustable air vents on each end. Ideal for kitchen growing, this fits as well on a porch or patio as it does in the garden.
Best Handmade Cold Frame
Another wooden cold frame, the Cedar Cold Frame Garden from Home Garden LLC features long-lasting, well-insulating cedar frame, a double-walled polycarbonate lid and 2- x 4-ft. of growing space.
Heavier than most, this will probably stay in one spot, but it’s attractive enough to be a centerpiece wherever you put it. And did we mention it’s handmade? It comes in sections easily assembled with a screwdriver, thanks to the easy-to-follow instructions.
