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Use Cold Frame for Gardening All Year Long

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Updated 1.23.24

Want to grow tomatoes and other crops year-round? You may want to consider using a cold frame for gardening.

A cold frame acts like a miniature greenhouse. It allows you to garden earlier in the spring, later into the fall, and even into the winter. Many gardeners find a cold frame to be much more versatile than a greenhouse because a small one can be movable. But first …

What is a cold frame?

A cold frame is a transparent, enclosed structure that lets in sunlight and prevents heat from escaping. It uses solar energy and insulation, rather than an extra heat source, to create a microclimate suitable for growing. A cold frame is built low to the ground to protect plants from wind and cold.

How to use a cold frame for gardening all season long with Tomato Dirt #GrowTomatoes #HomeGardening

What are the parts of a cold frame?

A cold frame for gardening has just two parts:

  1. The top: a cold frame has a light-permeable cover like glass, plexiglass, durable plastic sheeting, or greenhouse plastic that allows natural light into the structure. The top is built so that it can be propped open (“vented”) at different heights to prevent the interior from overheating.
  2. The sides: a cold frame’s sides create a supportive framework. They can be constructed of any durable material, such as plywood (the most common), stones, concrete blocks, or even bales of straw or hay – which are good insulators, inexpensive, and biodegradable. Typically, the cold frame’s sides are sloped toward the winter sun to capture as much light as possible.

You needn’t construct a base for your cold frame. Most gardeners simply set their cold frames on the soil. You may choose to grow crops directly in the area covered by the cold frame or in seed trays or containers placed inside the structure. If you decide to create a base for your cold frame, make sure it has holes for drainage.

What is the purpose of a cold frame?

You can use a cold frame for gardening throughout the growing season and beyond.

Use a cold frame for overwintering

Use a cold frame to over winter dormant plants, particularly tender perennials, like rosemary. Trim the plant before the first frost, dig up the root ball, place it in container, and back fill it. Sink the container into the cold frame soil. This way, heated ground will also help protect the dormant plant. Keep the soil moist.

Use a cold frame to start seedlings

Get a leg up on the growing season when you start tomato seeds and other crops in your cold frame. You can use seed trays or containers as plants germinate and then transplant seedlings to larger containers. This way, plants will become used to living outdoors – albeit in controlled conditions – making their transition to your garden easier. Plus, by using a cold frame, you needn’t dedicate part of your home to starting seedlings indoors.

And depending on the size of your cold frame, you may have more room to start several kinds of crops in succession as you move one set into the garden while you plant the other.

Use a cold frame to harden off seedlings

In the outdoor garden, your tomato plants have to stand on their own roots and deal with sun, wind, and critters. Gardeners use the process of hardening off to expose seedlings to the elements slowly, allowing plants toughen up gradually to reduce the shock of transplanting and reduce the possibility of injury. If you purchase tomato seedlings or other plants – or if start crops indoors – you can help acclimate them to their new home by placing them in a cold frame for a few hours each day.

Use a cold frame to extend your season

In the spring or fall, your forecast may call for a frost or freeze – one that is short-lived. If that’s the case, you can transfer your container plants into a cold frame for the night and then return them to the outdoors the next day when temperatures warm. Or in the fall, you can lift plants from their garden homes, place the root ball in a container, back fill it, and set them in your cold frame to continue to grow well into the winter.

You can also extend your growing season with your cold frame. Use it to grow cold weather crops throughout the off season, including lettuces, parsley, salad onions, spinach, radishes, and turnips, for instance.

How do I use a cold frame for gardening?

A cold frame acts like a greenhouse. The natural sunlight and warmth mean the cold frame’s interior can get warmer than you think. This can especially be the case during the fall and spring as days get longer and the sun is shining for longer periods. Heat can damage the plants.

To avoid overheating, lift the cold frame lid each morning and prop it open a few inches. Purchased cold frames may even come with a hinged mechanism for venting, but if not simply use a brick or piece of wood to allow a bit of air to circulate inside the structure. Be sure to close the cold frame lid before temperature go down in the evening.

What is the difference between a cold frame and a greenhouse?

There are two key differences:

  • A cold frame is short and sits low to the ground. A greenhouse is larger – many as big as a room in your home. A greenhouse can even be a separate building.
  • A cold frame relies largely on solar energy and insulation for heat. A greenhouse often includes an additional heat source.

Is there an easy way to make a DIY cold frame?

Yes – you can create a DIY cold frame for very little cost.

  • To create the lid: use old glass windows that you find at your local recycling center or thrift store. Another option is low-cost clear plastic – the thicker, the better.
  • To create the sides: use bales of straw, bricks or cement blocks, or plywood to create the cold frame structure.

Slope the cold frame’s roof towards the winter sun to capture light and to improve water runoff. Hinge the top for easy access. You can also add an electric heating cable to the cold frame’s interior to give your plants extra warmth on very cold nights.

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