A cold frame is a fantastic low cost item that enables you to keep less hardy plants alive during the cold winter months. They are often referred to as the halfway house between your greenhouse and garden.
By definition a cold frame is an unheated garden box that acts like a mini greenhouse. This small timber/metal or plastic structure with glass panelling provides protection for tender plants, cuttings and seedlings against wind, rain and freezing ground and air temperatures.
Choosing the right cold frame
Location
- You need to decide where you are going to put your cold frame and what are you planning to put inside of it. Your cold frame needs to be placed in a sunny spot that has space for you to work, kneel down and move around. A shady spot won’t give your plants enough light to stay warm so choose a spot that will receive lots of sunshine. Anywhere south facing is ideal. Putting your cold frame next to a building will add extra warmth and shelter.
- Ensure the location has good drainage.
- You can purchase cold frames in different lengths and heights so think carefully about what you are planning to grow inside and how high these plants will become.
Materials
Cold frames are available with either glass or plastic windows on the roof. Studies have found that glass retains heat far better that plastic however a twin-walled polycarbonate roof offers exceptional insulation and is becoming a very popular choice. If you have a small budget a plastic roofed frame will be cheaper than its glass alternative and also offers a far safer option which is beneficial if you have small children.
You will find a great variety in the materials used for the overall body of many cold frames. The majority are made completely of glass or plastic panels. These designs allow maximum sunlight into the cold frame. Other types available include aluminium or wooden frames.
Aluminium cold frames are reasonably priced and are lightweight which makes them easy to transport around your garden. They do not offer as much insulation as a wooden cold frame.
Wooden cold frames are a great choice as they offer great insulation and are extremely durable. If you are looking for a quality cold frame opt for one made from oak, however do bear in mind that they are the most expensive.
The Roof or ‘light’ design.
Cold frames come with either hinged or sliding lids. The lid provides light and can be moved to allow ventilation and access. A sliding lid will need extra clearance space around it.
Using your cold frame
Once you have bought your frame you can now use it to harden off seedlings that have started life indoors. You can also start annual seedlings off inside your cold frame to give them a head start on growing before the earth outside is ready to be planted in.
Problems to be aware of:
Hot weather
You must open the lid on hot days to prevent your plants overheating and dying.
Cold Weather
During extreme cold weather you must cover the cold frame with blankets or other forms of insulation to prevent your young plants from freezing. When the sun does return unwrap the cold frame to allow the sun’s rays to heat the frame once more.
In summary a cold frame offers a great way of enabling you to grow plants all year round. It offers the perfect alternative to a greenhouse if you have a small budget or garden. It is the perfect halfway house from the greenhouse to the garden for many young plants.
Jacks top tips for using a cold frame:
1 – Do your research; find out what plants and vegetables are happy to grow in colder climates.
2 – Lengthen the time your plants will grow by warming up your soil. Lighter soil warms up faster than denser heavier soil. You can add organic matter to your soil to lighten it.
3 – Cool your plants in the summer. The summer heat can be too intense for some plants and often results in drying certain species. You can help to combat this problem by adding mulch on to the soil to cool the bed and help it to retain moisture. Alternatively provide the plants with shade.
Good Luck
Gardener Jack
