A cold frame is an unheated outdoor structure that gardeners use to protect plants from cold weather. Cold frames prolong the growing season by providing a frost-free environment. They are usually used for cold-hardy vegetables and plants that require a head start in spring or a lengthened season in fall. With some simple materials and a weekend of work, you can construct a basic cold frame to fit your gardening needs.

Choosing a Cold Frame Design

When deciding how to build your cold frame, consider the size, style, and placement first.

Size

Pick a size that fits your available space and gardening plans. Smaller cold frames of 2ft x 4ft are good for starting seedlings and protecting a few plants. Larger structures up to 4ft x 8ft accommodate more mature plants. Make sure to account for the height of your tallest plants as well.

Style

Cold frames can have vertical walls straight up and down or sloped walls angled outward. Vertical walls may be easier to build but sloped walls allow more sun exposure.

Placement

Situate your cold frame in a sunny, south-facing location sheltered from strong winds. Nearby trees, walls, or fences can provide windbreaks. The site should be level, with well-drained soil and access to water.

Gather Materials

Cold frames are simple constructions that require only basic building materials:

Lumber for the frame (pressure-treated recommended)
Plexiglass or glass panes for the top and sometimes sides
Hinges, screws, and silicone caulk
Insulation (such as bubble wrap or straw bales)

Choose lumber dimensions suitable for your frame size. Plexiglass is inexpensive and durable. Single or double-layer glass tops also work well. Make sure to use greenhouse grade glazing materials.

Construct the Cold Frame Box

Follow these steps to build a classic slanted-roof cold frame:

Cut lumber to size according to your design plans. Miter (angle cut) corners to neaten the appearance.
Pre-drill screw holes to prevent splitting, especially in thinner lumber.
Assemble into a rectangle, attaching sides to front and back panels. Check corners are square.
Add the sloped roof panel, screwing into frames sides and front header. Caulk joints for weather-proofing.
Attach plexiglass or glass panes with silicone caulk and screws/hinges. Don’t caulk bottom edge for ventilation.
Add extra insulation like bubble wrap or straw bales as needed.
Install handles or lid braces to prop open the top on sunny days.

Prepare the Cold Frame Soil

To create ideal growing conditions inside your cold frame:

Loosen and amend the soil with compost or manure.
Mix in balanced organic fertilizer to enrich the soil further.
Consider adding heating cables buried in the soil for extra frost protection.
Install drip irrigation or a soaker hose if water access is limited.
Cover soil with black plastic or landscape fabric to retain heat and moisture.
Mulch over the ground cover with straw or leaves for additional insulation.

What to Grow in a Cold Frame

Cold frames allow for growing many plants outside of their normal seasons:

Cool-weather crops – Spinach, lettuce, kale, chard, peas, radish
Root crops – Carrots, beets, turnips, potatoes
Herbs – Parsley, cilantro, mints
Flowers – Pansies, snapdragons, osteospermum
Seedlings – Transplants for tomatoes, peppers, squash, melons

Check yourplants’ ideal temperature range and frost hardiness whenplanning. Avoid warm season crops that require higher heat.

Caring for Your Cold Frame

Cold frames need regular care and maintenance:

Ventilate on sunny days by propping up the lid for air flow.
Water when soil is dry to the touch. Avoid overwatering.
Monitor for pests like aphids and diseases. Remove affected plants promptly.
Weed inside the frame as needed to prevent competition.
Replenish spent soil with new compost/fertilizer between plantings.
Make repairs to the frame, glazing, or hardware over time as needed.

With proper use, a DIY cold frame can extend fresh garden produce for many seasons to come. The protected environment and head start helps plants thrive.

Frequently Asked Questions About Cold Frames

What are some cold frame design variations?

Other styles besides slanted-roof include A-frames, quonset hut shapes with hoops, trenches or pits dug in the ground, and converted window boxes. Shape and materials used can vary.

What if I want to build a larger cold frame?

Simply adjust the framing dimensions as desired. Use thicker lumber for larger sizes to support the weight. You may need help moving and assembling big sections.

What are some alternative glazing materials?

Fiberglass, polycarbonate, polyethylene film, and rigid insulation panels can all be used instead of glass. Choose greenhouse grade materials resistant to UV rays.

Should I insulate the walls as well as the lid?

Insulating the walls isn???t always necessary depending on your climate. Prioritize insulating the lid, then add side insulation if temperatures will be extremely low.

Can I attach automatic openers to the lid?

Yes, you can install automated piston or linear actuators that open the lid at set temperatures. This prevents overheating when venting is needed.

How long will my cold frame last?

With proper materials and maintenance, a cold frame can last 5-10 years or longer. Eventually the wood may rot, glass break, or hardware wear out.

Conclusion

Building your own cold frame is a relatively easy and affordable way to expand your gardening productive and growing seasons. With the right design, materials, and planting choices, you can enjoy homegrown produce beyond the typical frost-free dates. Take advantage of frost protection and warmer days by trying your hand at cold frame construction. Follow the steps outlined here to create a custom-sized structure that suits your needs and extends your harvest.

How to Build a Cold Frame