Greenhouse vs. Cold Frame: Which Is Better?
Greenhouses and cold frames are both valuable tools in any gardener’s arsenal, allowing you to keep your warm weather plants alive even in the dead of winter. They do some of the same things, so it’s easy to confuse the two.
However, they have some huge differences that you should know about before building your own greenhouse or cold frame. Let’s check out how they’re different and what they’re each good for below.
Overview of Greenhouse
Most people know what a greenhouse is by sight, but you’d be shocked how few people know what exactly they’re for beyond just growing plants. Greenhouses are structures or buildings designed to protect plants from weather, but you can also use them to grow offseason plants!
When you think of greenhouses, what’s the first image that pops to mind? For us, it’s a glass building with plants. Despite that, many greenhouses only use glass on top, or not at all. Many greenhouses only have glass or light-permeable plastic on top, using sturdier materials as the support walls.
What makes greenhouses special is their ability to grow plants in any season. To accomplish this, greenhouses are typically equipped with robust heating and climate control to keep plants as close to their preferred temperature as possible. Humidity may also be important, depending on the plant.
The climate controls go a long way, and there aren’t any real limits as to what you can grow in a greenhouse. You can grow seedlings, fruit, veggies, perennials, shrubs, and even trees if you have enough space! The main problem will be deciding what plants you want to grow because they’ll need to have similar requirements.
When to Choose
Unlike cold frames, greenhouses can be used to actively grow offseason plants during unforgiving winter conditions. This makes them great supplementary sources of fruits and veggies, but you can also use them to keep perennials and other plants alive through the winter. That helps later on because the plant doesn’t have to regenerate dead parts and can focus its energy on growth.
Use a greenhouse if you have a handful of plants you want to keep alive or grow through the winter, or if you have young trees that you need to shelter. Other possible uses include growing plants that don’t grow well in your native soil. For example, you’d need a greenhouse to grow tropical plants in Maine.
Lastly, you can use greenhouses to give your spring and summer plants a head start. Simply plant them a month or two before the season starts and then transplant them outdoors later.
Glass vs. Plastic for Greenhouses: Which Is Better?
Greenhouses are traditionally made with glass, which is aesthetically pleasing and great at trapping heat. For a long time, greenhouses were primarily made of glass because there simply weren’t other efficient options. Today, there are plenty of options, so glass isn’t always necessary.
Most people know polycarbonate plastic as the stuff eyeglass lenses and flexible plastic is made of, but it turns out to be excellent for making greenhouses. Polycarbonate is available in sheets or interlocking panels, but sheets are more popular because they’re cost-effective. The most important thing about polycarbonate is that it traps more heat than glass, which is especially useful when growing heat-loving plants in cold climates.
On the flip side, polycarbonate can heat up too much if the climate is already warm or hot, making your climate control system work harder. Your plants may suffer too because the temperature can vary a lot in the time it takes the climate control to vent the excess heat. Glass is a better choice when there aren’t major temperature deviations between your climate and the plants you’re growing.
Overview of Cold Frame
Cold frames aren’t widely known, and that’s probably because they’re little more than a box you keep soil and plants in. You can make them larger and fancier, of course, but a cold frame’s main purpose is to keep plants alive through the winter.
Most cold frames are only a few feet tall and wide, but you can make bigger ones. They can also be used to extend the growing season for fruit and veggie plants. In many cases, you can get a couple months of extra produce with cold frames.
A cold frame can be as simple or as complex as you’d like, but most of the time they don’t come close to the complexity of greenhouses. Fill the cold frame with soil or place it over soil—the latter helps eliminate transplant shock for delicate seedlings. During the day, you open the cold frame’s lid to let heat up and close it in the afternoon or night to keep the soil and your plants warm.
If you already live in a cool climate, cold frames have another handy use. You can start your cool season crops in them to get them started before the season, transplant them during the growing season, and put them back in the cold frame to extend the growing season. Used strategically, cold frames can keep your house stocked with veggies all year.
Compared to greenhouses, cold frames have several downsides. They’re usually less efficient at retaining heat than glass or polycarbonate plastic, so maintaining consistent temperatures is tricky. To test, put your cold frame in the sunniest part of your yard for a day. Use a thermometer and hygrometer to measure the temperature and humidity throughout the day and write your results down.
When to Choose
Use a cold frame to start cool season crops, extend crops’ growing seasons, and to keep seedlings or perennials alive. Because they’re typically small, we suggest using cold frames for your smaller plants and cooler veggie crops. If you want to grow crops out of season, you’ll have to invest in a greenhouse.
Greenhouses and cold frames are both extremely useful, but for different situations. Greenhouses are more flexible, allowing you to keep plants alive, start seedlings, and grow out of season plants. Cold frames, meanwhile, are mainly limited to extending cool weather crop growing seasons and keeping smaller plants alive.
See also: 8 Types of Greenhouses (with Pictures)
Featured Image Credit: Left: Irina Borsuchenko, Shutterstock, Right: JumpStory