The Complete Guide to Cold Frames and Cloches

The Simplest Way to Grow More

If there is one piece of equipment that transforms a vegetable garden from seasonal to productive, it is a cold frame. Not a greenhouse. Not a polytunnel. A cold frame — a box with a clear lid, sitting on the ground, doing nothing more complicated than trapping sunlight and keeping the wind off.

A cold frame extends the growing season by weeks at each end. It warms the soil in early spring so you can sow before your neighbours. It protects autumn crops from the first frosts so you harvest long after others have given up. It hardens off seedlings raised indoors without the daily carrying in and carrying out that drives every gardener to distraction. It overwinters herbs, salads, and hardy vegetables through the coldest months, providing fresh leaves when the garden is otherwise bare.

A cloche does the same thing on a smaller, more portable scale — protecting individual plants or short rows with a simple cover that goes on and comes off in seconds.

Neither requires electricity, heating, or any technology more advanced than hinges. They are among the oldest, simplest, and most effective tools in gardening — and among the most underused.

What Cold Frames and Cloches Actually Do

Sunlight passes through the transparent lid or cover and warms the air and soil inside. The enclosure traps this warmth, creating a microclimate that is consistently warmer than the surrounding garden. The temperature inside a closed cold frame on a sunny day can be 5–10°C (10–20°F) warmer than outside — enough to make the difference between a living crop and a frozen one.

Beyond warmth, both structures shelter plants from wind (which strips moisture from leaves and chills plants by evaporation), rain (which damages seedlings and promotes fungal disease on wet foliage), and — to some extent — pests (physical barriers deter slugs, birds, and flying insects).

They do not heat. They have no energy source other than the sun. On a still, overcast winter night, the temperature inside a cold frame will be only marginally warmer than outside. Their power is cumulative — warming the soil during the day, retaining some of that warmth overnight, and protecting from wind chill and rain. In combination, these effects are significant. Individually, none is dramatic. This is why expectations must be realistic: a cold frame is not a greenhouse. It will not grow tomatoes in winter. It will grow winter salads, protect overwintering herbs, and give spring seedlings a fighting start.

Cold Frames

How a Cold Frame Works

A cold frame is a bottomless box — typically with solid sides and a transparent, hinged lid (called the "light") — placed directly on the ground or on top of a raised bed. Sunlight enters through the lid, warming the air and soil inside. The solid sides retain the warmth and block the wind. The lid can be opened for ventilation when the temperature rises and closed to retain warmth when it falls.

The back of the frame is typically taller than the front, creating a sloped lid that faces the sun. This slope maximises the angle at which sunlight enters (particularly important in the low-sun months of early spring and late autumn) and sheds rainwater away from the opening.

Types of Cold Frame

#### Wooden Cold Frames {#wooden-frames}

The traditional choice — a timber box (cedar, pressure-treated softwood, or hardwood) with a glazed lid. Timber provides good insulation (the solid wooden sides retain warmth better than thin plastic or polycarbonate walls), a sturdy structure, and a natural appearance that suits most garden settings.

Strengths: Excellent insulation. Sturdy and stable. Can be built to any size. Easy to modify (add hinges, props, hooks, thermometers). Timber sides can be painted white internally to reflect light onto the plants, or black to absorb and radiate heat.

Limitations: Timber rots over time (pressure-treated or naturally durable timber lasts much longer). Heavier than aluminium or plastic frames. The wood itself is opaque — light enters only through the lid, not the sides.

Best for: Permanent or semi-permanent installations. Year-round use. Situations where insulation matters (cold climates, winter cropping).

#### Aluminium and Polycarbonate Cold Frames {#aluminium-frames}

Lightweight frames with aluminium structure and twin-wall or solid polycarbonate panels for both the lid and the sides. Light enters from all directions, creating a bright growing environment.

Strengths: Lightweight — easy to move. Transparent sides admit light from all angles (beneficial for seedlings). Polycarbonate is virtually unbreakable. Aluminium does not rot or rust. Many models include built-in ventilation and are designed for easy assembly and disassembly.

Limitations: Less insulating than timber — the thin polycarbonate sides lose heat faster than solid wood. Lighter weight means they are more vulnerable to wind (anchor or weight down in exposed positions). Can overheat quickly in direct sun due to the all-round transparency.

Best for: Spring hardening off. Portable use (moving around the garden as needed). Situations where light penetration is a priority. Milder climates where insulation is less critical.

#### Brick and Block Cold Frames {#brick-frames}

A permanent structure built from bricks, concrete blocks, or stone, with a glazed lid on top. The thermal mass of the masonry absorbs heat during the day and releases it slowly overnight — providing the best temperature stability of any cold frame type.

Strengths: Outstanding thermal mass (the warmest overnight temperatures of any cold frame type). Extremely durable — a well-built brick frame lasts decades. Heavy and stable — unaffected by wind.

Limitations: Permanent — cannot be moved. Requires construction skills (or a builder). More expensive than timber or polycarbonate alternatives.

Best for: Dedicated kitchen gardens. Year-round cropping. Gardeners willing to invest in a permanent structure for long-term use.

#### Straw Bale Cold Frames {#straw-bale}

The simplest improvised cold frame — arrange straw bales in a rectangle around the plants and lay an old window, sheet of polycarbonate, or pane of glass across the top.

Strengths: Almost free. Excellent insulation (straw is a remarkably effective insulator). Can be set up and taken down in minutes. The straw can be composted or used as mulch afterwards.

Limitations: Temporary — lasts one season before the straw deteriorates. Bulky footprint. Not elegant. Can harbour slugs and mice.

Best for: Emergency frost protection. Temporary season extension. Gardeners who want to experiment before investing in a permanent frame.

#### Raised Bed Cold Frames {#raised-bed-frames}

A glazed lid or hinged frame designed to sit on top of an existing raised bed, converting the entire bed into a cold frame. Some raised bed manufacturers sell compatible cold frame toppers; others can be improvised with hoops and polythene or polycarbonate panels.

Best for: Integrating season extension into an existing raised bed vegetable garden. See our Raised Garden Beds Guide for bed construction.

Glazing: Glass vs Polycarbonate

Glass retains more heat overnight than polycarbonate — it radiates warmth back into the frame more effectively. Glass is heavier (which provides stability), lasts indefinitely (if unbroken), and provides excellent light clarity. But glass is fragile — it shatters if struck or dropped, and broken glass in the garden is a safety hazard.

Twin-wall polycarbonate is virtually unbreakable, lightweight, and provides good insulation (the twin-wall construction traps an insulating layer of air between the two sheets). It transmits slightly less light than glass and can discolour with age, but for most practical purposes it is the safer, more convenient choice.

The practical advice: Polycarbonate is the default recommendation for most gardeners — safer, lighter, and adequate for the task. Glass is preferred by those who value maximum heat retention and light transmission and are willing to handle it carefully.

Sizing a Cold Frame

Depth (front to back): No wider than you can comfortably reach across — typically 60–120 cm (2–4 ft). You need to be able to reach the back of the frame without climbing inside.

Length: As long as you have space and need. Multiple shorter frames are more versatile than one very long frame, because you can manage ventilation and cropping independently in each.

Height: The back of the frame should be tall enough to accommodate the mature height of the crops you intend to grow. For seedling trays and low salad crops, 20–30 cm (8–12 in) at the back is sufficient. For taller crops (overwintering broad beans, kale), you need 40–50 cm (16–20 in) or more.

Ventilation: The Single Most Important Skill

A closed cold frame on a sunny day is an oven. The temperature inside can climb to lethal levels within minutes — even on a day that feels cool outside, even with cloud cover that breaks unexpectedly. Plants inside an unventilated cold frame on a sunny spring day will cook.

You must open the lid when the temperature rises and close it before dusk. This is the single most important management task for a cold frame user. Forget to open it on a sunny morning and you lose your plants. Forget to close it on a cold evening and you lose the protection you bought the frame to provide.

Propping the lid: Use a notched stick, a brick, or a dedicated prop stay with multiple height settings. Crack the lid a few centimetres on mild days; open it wide on warm days; close it completely on cold nights and during hard frost.

Automatic Vent Openers

A wax-cylinder automatic vent opener is one of the best investments any cold frame gardener can make. The device contains a cylinder of wax that expands as the temperature rises, pushing a piston that lifts the lid. As the temperature falls, the wax contracts and the lid closes.

No electricity. No batteries. No programming. The opener responds directly to the temperature inside the frame, opening and closing the lid automatically as conditions change. For anyone who cannot be present to ventilate the frame during the day — which includes most people who work away from home — an automatic opener prevents the overheating that kills more cold frame plants than frost ever does.

Check the weight rating. Automatic openers have a maximum lid weight they can lift — typically 5–7 kg for standard models. Ensure the opener is rated for the weight of your lid, including any accumulated rainwater or snow.

Positioning Your Cold Frame

Face the glazed lid toward the sun — south-facing in the Northern Hemisphere, north-facing in the Southern Hemisphere. This maximises the sun's entry angle and the warmth captured inside the frame.

Shelter from wind. Position the frame against a south-facing wall, fence, or hedge if possible. The structure behind provides a wind barrier and may radiate stored heat toward the frame.

Level ground with good drainage. A cold frame sitting in waterlogged soil creates damp, cold conditions inside — the opposite of what you want. Ensure the ground beneath drains freely.

What to Grow in a Cold Frame

Late winter to early spring: Sow salad leaves, radishes, spring onions, and early carrots directly in the soil inside the frame. The soil warms faster than the open garden, allowing germination weeks earlier.

Spring: Harden off seedlings raised indoors — tomatoes, peppers, courgettes, beans, squash. Place the trays in the frame, opening the lid progressively over seven to fourteen days to acclimatise the plants to outdoor conditions before planting out.

Summer: Remove or fully open the lid. Use the frame for propagating cuttings or raising late-season seedlings in the sheltered environment.

Autumn: Sow winter salads — lamb's lettuce, winter lettuce, mizuna, spinach, land cress — under the frame for harvest through the cold months. Protect late-season crops (final pickings of French beans, tomatoes, peppers) from the first frosts.

Winter: Overwinter herbs (parsley, chervil, coriander), hardy salad leaves, and spring-flowering bulbs in pots. Protect slightly tender perennial plants from the worst of winter weather.

Cloches

A cloche is a small, portable, individual plant cover — the cold frame's nimble, lightweight companion. Where a cold frame sits over a defined area permanently or semi-permanently, a cloche goes wherever you need it, for as long as you need it, and is moved or removed in seconds.

Bell Cloches (Glass and Plastic)

The original cloche — a bell-shaped dome placed over a single plant or small group of seedlings. Traditional bell cloches are hand-blown glass; modern equivalents are moulded plastic.

Glass bell cloches are beautiful, heavy (so they stay in place without pegging), and retain heat well overnight. They are also expensive, fragile, and provide no built-in ventilation — you must lift them to allow air circulation, or tip them slightly on a stone.

Plastic bell cloches are affordable, lightweight, and often include a built-in vent at the top. They need pegging or weighting to stay in place in wind. They retain less overnight heat than glass.

Best for: Protecting individual plants — newly transplanted seedlings, tender herbs, overwintering crowns (such as rhubarb for forcing). An attractive, traditional presence in a kitchen garden.

Lantern Cloches

A more ornamental design — a metal frame (cast iron, zinc-coated steel, or aluminium) with glass or polycarbonate panels, resembling a small lantern. Heavier and more decorative than bell cloches. The metal frame provides structure and the glazed panels admit light while sheltering the plant.

Best for: Decorative kitchen gardens. Protecting individual specimens where appearance matters. Winter protection for tender alpines and perennials.

Tunnel Cloches

A continuous low tunnel formed by hoops (wire, plastic, or metal) draped with polythene, fleece, polycarbonate panels, or mesh. Tunnel cloches cover entire rows of plants rather than individual specimens.

Strengths: Cover a large area efficiently. Adaptable — change the covering material to suit the season (polythene for warmth in spring, fleece for frost protection in autumn, mesh for pest exclusion in summer). Easy to lift one side for access to weeding, watering, and harvesting.

The default choice for productive vegetable gardens. A set of hoops and a roll of horticultural fleece or clear polythene is one of the most cost-effective season-extension investments any grower can make.

Best for: Row crops — salads, carrots, beetroot, peas, beans. Season extension in both spring and autumn. See our Netting, Fleece and Plant Protection Guide for covering materials.

Pop-Up and Net Cloches

Self-supporting fabric, mesh, or fleece covers with a spring or wire frame that pops into shape. Place over a plant or bed, peg down the edges, and remove when no longer needed. Compact to store.

Best for: Quick deployment for unexpected frost warnings. Pest exclusion (net versions). Temporary protection for individual plants or small groups.

DIY Cloches

A plastic bottle with the bottom cut off. An old window leaned against a wall. A sheet of bubble wrap over a hoop. Cloches lend themselves to improvisation — anything transparent or translucent that covers a plant and traps warmth serves the purpose.

The practical truth: A free DIY cloche that is in place tonight protects your plants better than an expensive cloche that is still in your shopping basket. Improvise when you need to. Invest when you can.

Choosing Between a Cold Frame and a Cloche

Cold frames are best for defined growing areas — a permanent or semi-permanent structure over a bed or section of garden where you manage crops through the seasons. They provide more consistent temperature control, are easier to ventilate (with hinged lids and automatic openers), and create a more stable microclimate. They are the serious season-extension tool.

Cloches are best for flexibility — protecting individual plants wherever they are in the garden, providing quick cover for unexpected frost, and moving with the crops rather than fixing the crops to one location. They are the responsive, portable solution.

Most productive gardeners use both. A cold frame for the dedicated salad bed and the hardening-off area; cloches for the newly planted courgettes, the vulnerable sweet peas, and the tender perennial that needs one more week of shelter before the last frost passes.

Seasonal Calendar

Late winter: Close the cold frame lid and warm the soil for two to three weeks before sowing the first early crops. Begin sowing salads and radishes inside the frame.

Early spring: Sow direct in the cold frame. Begin hardening off indoor-raised seedlings. Use cloches over individual transplants in the open garden. Ventilate the cold frame on sunny days.

Mid to late spring: Harden off tender crops (tomatoes, peppers, beans, squash) in the cold frame. Use cloches for frost protection on clear, cold nights. Remove cloches during the day as temperatures rise.

Summer: Open or remove cold frame lids. Use the frame for propagation or resting. Tunnel cloches with mesh covers for pest exclusion.

Autumn: Close the cold frame over autumn-sown salads and overwintering crops. Use cloches to extend the harvest of late-season crops. Protect tender perennials before the first hard frost.

Winter: Keep the cold frame closed except for ventilation on mild, bright days. Harvest winter salads from under the glass. Use cloches and fleece for emergency protection during severe cold snaps.

Materials: Durability and Lifespan

Glass: Lasts indefinitely if unbroken. Best heat retention. Fragile. Heavy.

Twin-wall polycarbonate: Ten to twenty seasons. Virtually unbreakable. Good insulation. Yellows slightly with age.

Solid polycarbonate: Similar to twin-wall but without the insulating air gap. Lighter. Less insulating.

Clear polythene: One to three seasons. Cheap. Degrades in UV. Adequate for temporary tunnel cloches.

Horticultural fleece: Several seasons with care. Breathable. Good frost protection. Not transparent — reduces light. See our Netting, Fleece and Plant Protection Guide for detailed fleece guidance.

Cedar or pressure-treated timber (sides): Fifteen to twenty-five years. Excellent insulation. Requires no chemical treatment (if pressure-treated).

Aluminium (frame): Indefinite. Lightweight. Corrosion-resistant.

Common Mistakes

Forgetting to Ventilate on a Sunny Day

The number-one killer of cold frame plants. A closed frame in sun overheats within minutes. Open the lid every morning that is not bitterly cold, and close it every evening. Or invest in an automatic vent opener and let the wax do the thinking.

Expecting a Cold Frame to Be a Greenhouse

A cold frame provides a few degrees of frost protection and shelter from wind and rain. It does not heat. On a still, freezing night, the temperature inside may be only marginally above outside. Do not plant tender crops in a cold frame and expect tropical performance.

Not Ventilating on Cloudy Days

Even on overcast days, the temperature inside a closed frame can climb higher than expected — particularly when clouds break unexpectedly. Check the frame on cloudy days, not just sunny ones.

Overwatering

The enclosed environment retains moisture. Plants in a cold frame typically need less watering than those in the open garden. Overwatering promotes fungal disease (botrytis, damping off) and root rot.

Positioning in Shade

A cold frame that does not receive direct sunlight captures minimal warmth and provides little benefit. Face the lid toward the sun and position in the sunniest available spot.

Using a Too-Small Frame

A cold frame that is too shallow restricts the crops you can grow. Allow adequate height for the mature crop, not just seedlings.

Pre-Purchase Checklist

• What will you use it for — hardening off, season extension, winter cropping, or all three?
• Cold frame or cloche — do you need a fixed structure over a defined area, or portable protection for individual plants?
• What material for the sides — timber (best insulation), polycarbonate (lightest, transparent), or brick (permanent, thermal mass)?
• What glazing — glass (best heat retention) or polycarbonate (safer, lighter)?
• Is the frame deep enough for the crops you intend to grow?
• Can you reach across the frame to access the back without climbing inside?
• Does the lid hinge open easily and stay open at multiple heights?
• Will you install an automatic vent opener (strongly recommended)?
• Where will you position it — south-facing, sheltered, on well-drained ground?
• For cloches: what type suits your needs — bell (individual), tunnel (rows), or pop-up (quick protection)?
• For tunnel cloches: do you have hoops, pegs, and covering material?

Why Buying Through Amazon Makes Sense

Amazon stocks cold frames and cloches from compact starter units to substantial timber frames, plus the automatic vent openers that make cold frame management practical for people who work away from home during the day. Product listings include dimensions, materials, glazing type, and weight ratings.

Customer feedback is particularly valuable for cold frames, because the real test comes after a season of daily use — does the hinge mechanism survive repeated opening and closing? Does the glazing stay clear after a winter of frost and rain? Does the frame hold together after wind, weight, and temperature cycling? Reviews from growers who describe their climate, their crops, and their results over a full season provide the practical truth that photographs alone cannot convey.

Amazon Marketplace Protections

When you purchase through Amazon, several consumer protections apply. Products sold directly by Amazon are covered by standard consumer rights legislation, including the right to return items within a specified period.

For products sold by third-party sellers on the Amazon Marketplace, the A-to-Z Guarantee provides additional protection. If an item does not arrive, arrives damaged, or is materially different from what was described, Amazon will investigate and, where appropriate, issue a refund.

Amazon Renewed products — professionally inspected and restored items — come with their own guarantee, providing confidence when purchasing pre-owned equipment at reduced prices.