Domakihub How to Build a Cold Frame and Grow Year-Round
A simple DIY box with a glazed lid that adds weeks to your growing season.
Reviewed by Domakihub garden pros · 2026-06-23 · 5 min read
A cold frame is one of the most cost-effective garden structures you can build — a low box with a transparent lid that traps solar heat and shields plants from wind and frost. The video above walks through the carpentry in real time; the steps below give you the planning context and material choices that matter most for Greek conditions, where mild but unpredictable winters can catch seedlings off guard. Whether you manage a family home in Athens, a hillside villa in Crete, or a holiday rental property with garden space, a cold frame keeps herbs, salad leaves, and seedlings productive from autumn straight through to spring.
What a cold frame actually does
A cold frame works on the same principle as a greenhouse but at ground level. The transparent lid — glass, polycarbonate, or even a recycled window sash — allows sunlight in while preventing convective heat loss overnight. On a sunny winter day in Greece, the interior can sit 10–15 °C warmer than the outside air, which is enough to keep cold-tolerant crops growing and to nurse seedlings that would otherwise stall.
Unlike a heated greenhouse, a cold frame needs no electricity or gas. It is entirely passive, which makes it ideal for properties where you want low-maintenance productivity — rental gardens that need to look attractive and yield fresh herbs for guests, or kitchen gardens that must survive weeks without an attentive caretaker.
Choosing your materials in a Greek context
Traditional cold frames use rot-resistant timber such as cedar or treated pine for the sides and a recycled single-glazed window for the lid. In Greece, salvaged aluminium-framed glass panels are easy to find at reclamation yards (παλαιοπωλεία) and make excellent, durable lids. Polycarbonate sheet is lighter, shatterproof, and widely stocked at hardware chains, making it the safer option for properties with children or guests.
For the frame itself, stone or brick are permanent alternatives to timber — particularly fitting for older properties with leftover masonry materials. Whatever you use, the back of the box should stand roughly 30 cm taller than the front so the sloping lid sheds rainwater and angles toward the sun.
How to build a cold frame in 5 steps
- 1
Select your site and take measurements
Position the cold frame against a south-facing wall or fence to maximise winter sun exposure and gain extra radiated warmth from the masonry. Measure your salvaged window or polycarbonate panel first — the frame is built to fit the lid, not the other way around. Note the dimensions and add 2–3 cm tolerance on all sides so the lid seats properly without binding.
- 2
Cut and assemble the timber sides
Cut the back board to the full width of the lid and set its height at roughly 40–45 cm. Cut the front board to the same width but only 25–30 cm tall. The two side boards must be cut with an angled top edge that descends from back height to front height — mark this diagonal with a straight edge and cut with a circular or hand saw. Drill pilot holes and join all four sides with galvanised screws or exterior wood joinery screws to prevent rust.
- 3
Treat and weatherproof the timber
Apply a non-toxic wood preservative or exterior-grade linseed oil to all surfaces before assembly if possible, and again to any cut ends afterward. Avoid creosote or solvent-based preservatives that can off-gas onto edible plants. Allow 24 hours of drying time before placing the frame in its final position on level ground.
- 4
Fit the lid and add ventilation
Lay the glass or polycarbonate panel across the top of the box. Hinge it at the back using two rust-proof butt hinges so it can be propped open for ventilation on warm days. Cut a short length of timber or dowel — roughly 30 cm — to act as a prop stick. On any day when the outside temperature exceeds 10 °C, open the lid partially to prevent overheating and damping-off disease in seedlings.
- 5
Prepare the interior and plant up
Fork over the soil inside the frame to a depth of 20 cm and work in a handful of well-rotted compost per square metre. Plant cold-tolerant crops directly — spinach, rocket, lamb's lettuce, parsley, coriander — or stand potted seedlings inside for hardening off before transplanting to open beds. Water sparingly, since the lid prevents rain from entering; check soil moisture every two to three days and ventilate on bright days to avoid humidity build-up.
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FAQ
- Can I use a cold frame all year round in Greece?
- Primarily in autumn, winter, and early spring. Greek summers are too hot for most cold-frame crops — the trapped heat would scorch plants. In summer, remove or prop the lid fully open and use the box as a regular raised bed, or store it until cooler weather returns.
- What is the best glazing material — glass or polycarbonate?
- Both work well. Glass transmits slightly more light and looks more attractive, but it is heavier and can shatter, making polycarbonate the safer choice for holiday rental properties or homes with children. Twin-wall polycarbonate also offers better insulation than single-pane glass.
- How do I stop condensation dripping onto seedlings?
- Tilt the lid at a steeper angle so water runs to the back rather than dripping straight down. Open the frame for 30–60 minutes each morning when temperatures allow, and avoid overwatering. A light sprinkling of grit or perlite on the soil surface also improves drainage and reduces damping-off risk.