Grower's Guide: What is a Cold Frame Greenhouse?

Cold frame greenhouse vegetable garden
May 22, 2018

If you’ve been looking for ways to extend your growing season or start warm-weather seedlings early, you may have come across the term “cold frame greenhouse.” These outdoor plant shelters can protect your precious plants from winter weather and make sure your plants are ready to go in the ground as soon as spring has sprung.

Want to learn more about cold frame greenhouses and whether they’re right for you? You’re in the right place! The following guide will tell you everything you need to know.

cold frame greenhousecold frame greenhouse

What Is a Cold Framer Greenhouse

A cold frame greenhouse is a clear, insulated outdoor structure that protects plants. Unlike a traditional greenhouse, which often uses gas or electric heat, a cold frame greenhouse depends on the sun’s warmth to create a safe microclimate for your garden. It protects plants from wind and cold without the risk of burning them.

While it is possible to find a small cold frame greenhouse, most are very large and used for commercial growth. These are also known as high tunnel greenhouses.

How Are Cold Frame Greenhouses Used?

Cold frame greenhouses are most useful during the period that starts a few weeks before the first frost of the year and continues until a few weeks after the last frost. Since many regions in the United States experience unpredictable weather during this transitional time, cold frames help protect growers from losses due to unexpected changes. Here’s a closer look at some of the ways people commonly use their cold frame greenhouses.

Extending the Growing Season

Cold frame greenhouses are excellent for growing cool-season plants that are equipped to withstand lower overnight temperatures. Since cold frames create a more controlled climate and maintain warmer temperatures, they allow you to start your plants early and harvest them later without worrying about them dying due to exposure to frost. Generally, you can expect your cold frame to keep the soil and plants five to 10 degrees warmer than the ambient outdoor temperature.

Overwintering Dormant Plants

While a cold frame won’t allow you to grow delicate plants during the winter, it’s still useful during the cold season. Instead of winterizing your greenhouse, you can use it to protect plants during their dormancy. To do this, you may want to partially cover your cold frame so you can minimize the plants’ exposure to sunlight. You’ll also want to make sure you maintain adequate soil moisture. These two steps will ensure the plants don’t grow while also preventing them from completely drying out.

Hardening Seedlings and Delicate Plants

If you have indoor plants or seedlings you want to move outside, you’ll need to gradually get them used to the changes in sunlight, temperature, and moisture. A cold frame allows you to control the environment somewhat so the plants can get used to being outside. Once your plants have adjusted, you can plant them outdoors in your garden.

growing greenhouse in fieldgrowing greenhouse in field

Who Uses Cold Frame Greenhouses

High tunnel cold frame greenhouses are typically used by commercial growers for large-scale farming and serious gardening enthusiasts. If you produce crops for a farmer’s market or an urban farm, then a cold frame greenhouse might be right for you.

Home gardeners who are serious about producing large crops, have enough space, and live in areas where the weather is unpredictable can also benefit from investing in a cold frame.

Features and Benefits

ShelterLogic’s cold frame greenhouses are the ideal commercial high tunnel growing shelter. They’re made of 100% galvanized steel, so they’re resistant to both rust and corrosion. Since there’s no exposed raw steel, these are some of the most durable greenhouses on the market. They're available in either round or gothic style, and all of the frames come with corner braces and all the hardware you need to assemble them.

Aside from protecting you from the heartbreak of losing the plants you’ve worked so hard to grow, one of the biggest benefits of using a greenhouse is the money you'll save. By using your cold frame to start seeds, you’ll save yourself from having to buy started plants from the nursery. It’s easier than you might think to start your own seeds, and doing so allows you to avoid having to deal with pests or pathogens that might hitch a ride on nursery plants. This will also save you the cost of having to buy pesticide treatments to get rid of them.

When you grow your own seeds, you'll have the opportunity to choose the hardiest and healthiest-looking plants from the bunch. This will give you a head start towards enjoying an amazing growing season. By extending the amount of time you can grow your crops, you’ll also be able to enjoy fresh, home-grown produce for longer. This will also allow you to spend less at the grocery store.

Cold frame greenhouse vegetablesCold frame greenhouse vegetables

What Can You Grow in a Cold Frame Greenhouse?

You can grow a large variety of crops in cold frame greenhouses. When planning your growing season, remember that cold frames don't provide an additional heat source to keep your plants warm in the frigid months. Here’s a closer look at a season-by-season crop schedule for an unheated greenhouse.

Early Spring (Feb. – April)

You can use your cold frame to grow hardy early crops and cool-season root crops from February through April. Some of the vegetables to plant at this time include:

  • Lettuce
  • Spinach
  • Arugula
  • Kale
  • Cabbage
  • Broccoli
  • Chard
  • Cauliflower
  • Scallions
  • Radishes

You can also start growing carrots, onions, radishes, and beets from seed and eventually harvest them from the soil under your frame.

Late Spring (April – May)

As things warm up a bit, you can start growing warm-season crops in your cold frame. This includes:

  • Cantaloupe
  • Tomatoes
  • Beans
  • Pumpkins
  • Celery
  • Melons
  • Corn
  • Peppers
  • Eggplant
  • Squash

It’s important to make sure your cold frame doesn’t become overheated in hot weather. Otherwise, you’ll end up with plants that are weak and spindly. The best way to do this is to ensure you have plenty of ventilation.

While you’ll have a lot of growing options during the late spring, it’s important not to mix warm-weather and cool-weather crops in your frame at the same time. Since they have different temperature requirements, you’ll have trouble maintaining conditions that keep them both happy.

When it gets warm enough that you no longer need to worry about protecting your plants, you can clean and sanitize your greenhouse so it’s ready for the next cold season.

Growing lettuce in a greenhouse gardenGrowing lettuce in a greenhouse garden


In the fall, you can use your cold frame to extend your harvest of warm-weather summer crops and to grow salad greens or other compact cool-weather crops. This growing season typically runs from late August until sometime in December.

Generally, you’ll want to sow your seeds in August or September so your plants can grow to near maturity before the first frost. Once the daily sunlight falls below 10 hours, your plants will stop growing. However, they will remain for several weeks thereafter.

Some of the crops to grow in the autumn include:

  • Lettuce
  • Radishes
  • Cabbage
  • Cauliflower
  • Spinach
  • Kale


The winter is the harshest time of year to grow plants, so this is when you’ll want to stick to the hardiest varieties. Sowing seeds in January will likely yield you a March harvest.

Some of the crops you can grow in winter include:

  • Leeks
  • Parsley
  • Arugula
  • Spinach
  • Lettuce

You can also use your cold frame to over-winter vegetables like Brussels sprouts, kale, cabbage, and cauliflower. While they won’t grow during the winter season, you can keep them safe until they can provide new growth in the spring.

When storing winter root vegetables – like carrots, potatoes, parsnips, and beets in your cold frame during the winter, be sure to cover them with straw to keep the soil from freezing.

Maximize Your Harvest with a Cold Frame Greenhouse

There are so many benefits to using a cold frame greenhouse. If you’re interested in adding one to your property, ShelterLogic has the perfect solution for you.

ShelterLogic offers a selection of customizable cold frame greenhouses so you can choose the size and style you need. To get started, you’ll choose your high tunnel greenhouse bundle, select the size and style you want, and check out.

Don't need the large-scale capabilities of a high tunnel greenhouse? We also have a selection of other greenhouses to choose from, so you’re sure to find one to meet your needs. If you're not sure how to choose the best greenhouse for you, you can always contact us. Our experts will be happy to help you find the perfect solution for your growing needs.

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