About Our Cold Frames
A cold frame is essentially a miniature greenhouse without heating—a transparent box that traps solar warmth to extend your growing season by 6-8 weeks at both ends. Unlike mini greenhouses, cold frames sit directly on the ground, creating a protected microclimate perfect for hardening off seedlings, growing winter salads, and protecting tender plants from frost.
Our collection features premium Access cold frames and Elite cold frames built with rust-proof aluminium frames and your choice of toughened glass or twin-wall polycarbonate glazing. Every model includes sliding roof windows for ventilation control, built-in gutters for rainwater management, and removable staging shelves. Prices start from £249, and all cold frames come with free UK delivery and warranties ranging from 10 to 25 years.
The difference between a £200 wooden cold frame and our aluminium models? You'll still be using ours in 2050.
Why Aluminium Frames Beat Wood and Plastic
Most cold frames on Amazon and at garden centres use wooden or plastic frames. Here's why that's a problem: wooden frames rot within 3-5 years despite treatment, and plastic frames crack in UV light and blow away in strong winds. We've seen both failures countless times over our 15+ years in business.
Aluminium frames solve both issues permanently. Our Access and Elite models use powder-coated aluminium that won't rust, rot, or degrade. The frames need zero maintenance—no annual re-treating with wood preservative, no replacing broken plastic corners. Access cold frames carry a 15-year frame warranty, Elite models extend that to 25 years.
The weight difference matters too. A 4x4 aluminium cold frame weighs 22kg—heavy enough to stay put in storms, light enough for one person to move if you redesign your garden layout.
Toughened Glass vs Polycarbonate: Which Glazing?
Toughened Glass transmits 92% of available light compared to polycarbonate's 83%, which matters significantly for winter growing when light levels naturally drop 60% compared to summer. Glass stays crystal clear for decades, doesn't scratch when you're reaching over it, and looks more attractive. Our toughened glass cold frames use 4mm safety glass that won't shatter into dangerous shards if broken.
Twin-Wall Polycarbonate provides 20% better insulation than glass, typically maintaining 1-2°C warmer overnight temperatures. This matters if you're overwintering borderline-hardy plants or starting seeds in February. Polycarbonate is virtually unbreakable—perfect if you have children playing nearby or your garden gets hit by footballs. The trade-off is a slight reduction in light transmission and the panels can yellow after 15-20 years.
For most gardeners growing salads, hardening off bedding plants, and protecting pots over winter, glass offers better value long-term. Choose polycarbonate if maximum insulation or safety is your priority.
Choosing Your Cold Frame: Size and Placement
Size Matters More Than You Think
The most common mistake is buying too small. A 2x4 cold frame looks adequate in photos but only holds 12-16 seed trays or 4-5 lettuce plants. Most gardeners quickly discover they need more space.
A 4x4 cold frame provides 16 square feet—enough for 30-35 seed trays, a full season of cut-and-come-again salads for two people, or overwintering 20-25 potted plants. This size hits the sweet spot for typical UK gardens.
If you're growing for a family or selling produce, the 4x8 and 6x4 models offer professional capacity without the heating costs of a greenhouse. Our largest 8x4 cold frame can accommodate 70+ seed trays simultaneously.
Siting Your Cold Frame
Place your cold frame on a south-facing site to maximize winter sun exposure—this can mean the difference between frost damage and healthy growth on clear January nights. The structure can sit directly on soil, paving slabs, or gravel. If placing on soil, level the ground first and consider laying a weed membrane underneath to prevent growth inside.
Avoid sites under trees where falling leaves will block light and drip moisture onto the frame constantly. Position within hose reach since you'll be watering regularly during spring and summer. If you're concerned about creating a proper foundation, read our guide to bases which explains simple levelling techniques.
Cold frames work beautifully alongside lean-to greenhouses in stepped growing systems—use the greenhouse for raising seedlings, move them to the cold frame for hardening off, then plant outside.
How to Use a Cold Frame Throughout the Year
- Spring (March-May): Hardening off season. Move seedlings from indoors 2-3 weeks before planting out, gradually increasing lid ventilation each week.
- Summer (June-August): Grow heat-lovers like chillies and melons. Remove roof panels for ventilation or you'll overheat the plants.
- Autumn (September-November): Sow winter salads and herbs. Close at night to protect from frost, open on mild days.
- Winter (December-February): Overwinter tender perennials, start hardy annuals early. Cold frame stays 3-5°C warmer than outside.
How to Harden Off Plants: Step-by-Step Guide
Hardening off prevents transplant shock when moving greenhouse or indoor-grown plants outside. Sudden exposure to wind, temperature fluctuations, and direct sunlight can stunt growth or kill young plants entirely.
- Week 1: Lid closed at night, open 2-3 inches during warm hours.
- Week 2: Increase to 6-8 inches ventilation; close at night.
- Week 3: Lid fully open unless frost is forecast—plants are now hardened off.
Properly hardened plants show darker green foliage and stronger stems—ready for outdoor life.
Managing Your Cold Frame: Ventilation and Pests
Controlling Condensation: Excess moisture causes damping off. Prop lid 1-2 inches open even on cold nights unless below -3°C. Our sliding roof panels allow fine adjustment to airflow.
Slug and Snail Control: Check corners weekly, use copper tape or gravel barriers. Avoid pellets—lift pots on staging to improve airflow and reduce pests.
Key Features of Our Cold Frame Collection
- Rust-Proof Aluminium Construction: 15-25 year warranties, zero rot or corrosion
- Sliding Roof Panels: Infinite ventilation adjustment for precision climate control
- Built-In Guttering: Prevents waterlogging, channels rainwater away
- Removable Staging Shelves: Two-tier growing maximizes capacity
- 4mm Safety Glazing: Toughened glass or twin-wall polycarbonate options
- Integral Aluminium Base Rail: Weatherproof seal and superior rigidity
Frequently Asked Questions about Cold Frames
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What is a cold frame used for?
A cold frame extends your growing season by 6-8 weeks at both ends by trapping solar heat without electricity. Use it for hardening off seedlings, growing winter salads, starting seeds early, and protecting plants from frost.
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How much does a good cold frame cost?
Quality aluminium cold frames start from £249 for a 2x4 model, £450-650 for 4x4, and up to £1,275 for 8x4 premium models. Wooden versions cost less initially but need replacing within 3-5 years.
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Can I use a cold frame in winter?
Yes. Cold frames protect from frost and wind, maintaining 3-5°C warmer temperatures than outside air. Ventilate on mild days to prevent fungal issues.
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What's the difference between a cold frame and a mini greenhouse?
Cold frames sit on the ground with top access, providing better frost protection. Mini greenhouses have vertical sides and more headroom—better for tall plants or general year-round use.
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How do I stop condensation in my cold frame?
Prop the lid 1-2 inches open even on cold nights unless below -3°C. Avoid overcrowding, and use staging to lift pots for airflow.
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Are Access or Elite cold frames better value?
Access offers 15-year warranties; Elite extends to 25 years. Aluminium frames need zero maintenance—no repainting or re-treatment, unlike wood which lasts 3-5 years.
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Does a cold frame need a base or foundation?
No permanent base needed. Place directly on soil, paving, or gravel—just ensure it’s level. See our guide to bases for simple levelling methods.
Ready to Extend Your Growing Season?
Browse our complete range of cold frames above, from compact 2x4 models to 8x4 professional frames. Every cold frame includes free UK mainland delivery and optional installation. For help choosing size or glazing, call 0800 098 8877 or email sales@greenhousestores.co.uk.