Are you debating a cold frame vs greenhouse for your garden? If you’re wondering which is the best option for your winter plant growing, this post has lots of information to help you decide.
Cold frame vs Greenhouse: which is right for me?
While a cold frame and a greenhouse are both used to grow plants, there are some major differences between the two.
The first and most obvious is cost; there is a significantly higher cost to building and maintaining a greenhouse.
At the same time, a cold frame and a greenhouse each have a different level of functionality which may negate the cost factor. For example, a cold frame can’t be used for trees or your favourite flowering shrubs. However, a cold frame is much cheaper to make and is easy to install, so it may be worth using one for a couple of seasons to see if it meets your needs.
What Are the Uses for a Cold Frame?
Generally, a cold frame is an unheated, bottomless box with a lid. It relies on exposure to the sun to warm the space and the soil within. The lid is opened or closed to regulate the temperature and for ventilation.
A cold frame can be purchased already constructed, as a kit that you assemble, or it can be a DIY project made from scrap wood and an old glass window or door as the lid.
There are several ways to use a cold frame, including:
1. Protecting Tender Perennials in Winter
If you have perennials that are going to need protection to survive the winter, a cold frame could be the answer. Generally you won’t be actively growing perennials in winter, and will instead keep them dormant in your cold frame. If your plants are not potted, you can dig them out and temporarily pot them up – just make sure you allow enough room for the root ball to be surrounded with soil.
Pack the pots into the cold frame, and water them well. It’s a good idea to cover the plants with a good layer of insulating material like straw or mulch, making sure to fill in any gaps between the pots. Use a cover on the window to prevent the sun from reaching the plants, as this can encourage them to start growing too soon.
The cover will also minimise significant temperature fluctuations. To better monitor the temperature, keep a thermometer inside your cold frame, and then open or close the lid to regulate as needed.
2. Extending the Growing Season
This is particularly important if you like to grow your own fruit and vegetables. By planting them in a cold frame you can extend the growing season by a couple of months. Plant your seeds directly in the soil of the cold frame, or use containers to grow them in.
In the late autumn, daytime temperatures may be great for these plants, but nighttime temperatures are significantly cooler. You may have the cold frame completely open during the day, and close it in the late afternoon to keep the heat inside for the night.
If you use a cold frame effectively, it’s not unusual to be eating fresh salads right through winter.
3. Starting Your Seedlings
This works especially well for cool weather crops like greens, and brassicas including broccoli, cauliflower and cabbage. You want the sun to enter the cold frame with these crops, so make sure the lid is unobstructed. Allow the sun to warm the soil by keeping the lid closed for about two weeks before you plan to plant.
Plant your seeds as you would in trays or individual pots, and place them in your cold frame. Keep a close eye on the temperature in your cold frame as the days get longer and the sun is higher in the sky; you may need to vent it by opening the lid to regulate the temperature. Also, keep a close eye on the moisture level of your seedlings – they can dry out very quickly in a cold frame. The reason that plants die in a cold frame isn’t usually because of the cold, it’s more often due to excessive heat and lack of humidity.
If your cold frame is portable, you can place it in the garden and plant directly into the soil. This gives the added advantage of eliminating transplant shock for your seedlings.
What Are the Uses for a Greenhouse?
A greenhouse is a much larger structure than a cold frame, and as such it’s usually a static outdoor building. Traditional greenhouses were just that — a house, but with glass walls and ceiling. Today, you can have that same traditional greenhouse, but there are also high tunnel-style greenhouses consisting of an arched frame covered with plastic sheeting.
As with a cold frame, your greenhouse can be built for you, or you can purchase a kit to assemble it yourself. It’s also possible to construct a greenhouse out of salvaged windows and doors, but this does require some building experience. This type of greenhouse will be unique from any other and can be a real feature in your garden.
While a greenhouse is usually much more expensive than a cold frame, it has some definite advantages, including:
1. Growing All Year Round
A greenhouse gives you the option to control the climate via a heating system that will keep it warm even in winter. This means you can grow food and ornamental plants all year round. You could even use your greenhouse to grow tropical plants, including orchids or citrus fruit. And because a greenhouse usually has a high ceiling, you can also grow taller trees and shrubs that wouldn’t fit in a cold frame.
2. Growing From Seed
This benefit is shared with a cold frame, but on a much larger scale. You can grow enough food to feed your family, and you can start lots of flowers from seed at a fraction of the cost compared to buying started plants. You can also use your greenhouse to force spring bulbs, or grow amaryllis bulbs for Christmas.
3. Controlling the Environment
Even with a cold frame, the weather can impact your success. A greenhouse can be controlled with heaters, lights, and sensors that will automatically open vents when necessary. Consequently, the weather outside isn’t as much of an issue. Of course, running these systems will cost additional money, but it protects your plants even when you can’t be home, which in turn avoids the cost of replacing weather-damaged plants.
4. Growing Organically
With a greenhouse, you can garden organically without worrying about chemical drift from farms or even the neighbours using chemical pesticides and herbicides.
As you can see, there are many benefits to using both a cold frame and a greenhouse. Of course, the main reason to choose one of these pieces of garden equipment is to extend the growing season, but the option you go for should be influenced by the amount of space you need to grow plants, the amount of space you have available in your garden, and your budget. Think carefully about the pros and cons of a cold frame vs greenhouse before making a final decision.
Do you have experience of using a cold frame or greenhouse in your garden? Which option would you recommend?