Building a Cold Frame: Plans, Kits and What to Grow in It
A practical, no-nonsense guide to DIY plans versus buyable kits — and exactly how to use one to harden off seedlings, overwinter tender plants and grow salads through the cold months.
If there's one piece of kit that punches far above its price and complexity, it's the humble cold frame. It's essentially a bottomless box with a transparent, sloping lid that sits directly on the ground, traps solar warmth and gives your plants a sheltered microclimate. No heating, no electricity, no fuss. Yet in my experience it quietly transforms how — and when — you can grow.
The reason a cold frame earns its place in almost any garden is simple: it does a handful of jobs exceptionally well. It hardens off seedlings before they face the open garden, it overwinters tender plants that would otherwise sulk or die, and it lets you grow low crops like salads and strawberries when the rest of the plot has gone to sleep. Across the season, a well-sited frame can extend your growing window by roughly 6–8 weeks at each end — a meaningful chunk of extra cropping time for something you can build in an afternoon.
In this guide I'll walk you through the genuine decision most gardeners face: should you build your own cold frame from scrap, or buy a ready-made kit? I'll cover plans, materials, what to grow, and the honest trade-offs of each route. Whether you're a thrifty improviser with a salvaged window in the shed or someone who'd rather click "buy" and be done, there's a sensible path here.
What a Cold Frame Actually Does
Before we talk about building or buying, it's worth being clear about the three core jobs a cold frame is brilliant at. Get these straight and you'll size and site your frame correctly from the outset.
The frame sits at ground level and traps solar warmth, which is why a sunny, south-facing position against a wall is the gold standard. That wall acts as a thermal store, releasing warmth slowly through the night. The sloping lid does double duty — it sheds rain and snow, and it tilts the glazing towards the low winter sun so you capture as much light as possible when daylight is scarce.
Hardening off seedlings
Plants raised indoors or in a greenhouse are tender. The cold frame is the halfway house, letting them acclimatise to cooler, brighter, breezier conditions over a week or two before final planting out.
Overwintering tender plants
Marginally hardy plants, autumn-sown hardy annuals and dormant tubers ride out the winter under cover, protected from the worst of the frost, wind and wet.
Growing low crops
Salad leaves, spinach and strawberries thrive in the low, sheltered space, giving you fresh pickings well outside the normal season.
DIY or Kit? The Core Decision
This is the question that brings most people to the topic, so let's tackle it head-on. Both routes deliver the same fundamental microclimate, but they suit very different temperaments and budgets.
A DIY cold frame is gloriously cheap if you've got materials lying about. Built from scrap lumber and a salvaged old window, you can put one together for around $20–$50. If you're truly resourceful, old windows and leftover timber can bring the whole thing in under $20. Kits, by contrast, generally run from around $50 to $200 at the affordable end, climbing well beyond that for premium aluminium-and-toughened-glass models.
| Consideration | DIY Cold Frame | Ready-Made Kit |
|---|---|---|
| Typical cost | Under $20 to $50 from scrap | From around $50 to $200+ |
| Build time | An afternoon (with materials to hand) | Flat-pack assembly, often under an hour |
| Materials | Salvaged window, leftover timber | Aluminium, polycarbonate or toughened glass |
| Customisation | Total — any size or shape you like | Fixed dimensions per model |
| Durability | Depends on your materials and finish | Engineered for years of outdoor use |
| Looks | Rustic to ramshackle, your choice | Neat, consistent, garden-tidy |
Pro Tip
If you already have an old single-glazed window in the garage or shed, the DIY route is almost always the smart play. The glazing is the most expensive part of any frame, and a salvaged window hands it to you for free. Just check there's no flaking lead paint if it's a genuinely old frame.
The case for building your own
Beyond the obvious cost saving, building your own means you control the dimensions absolutely. Got an awkward corner against a south wall? Build to fit it. Want a deeper frame for taller overwintering pots? No problem. There's also real satisfaction in it — a cold frame is one of the few garden structures genuinely achievable for a beginner with a saw and a screwdriver.
The case for a kit
Kits win on convenience, consistency and longevity. The better models use twin-wall polycarbonate or toughened glass set into aluminium frames designed to shrug off years of weather. If you're not confident with tools, or you simply want a tidy, predictable result, a kit removes all the guesswork. The trade-off is the fixed footprint and the higher entry price.
DIY Cold Frame Plans: Getting It Right
There's no shortage of free plans floating around, and the good news is that the basic geometry is forgiving. The principle every plan shares is the same: a bottomless box with a back taller than the front, so the lid slopes forwards and down. That slope wants to face the midday sun — south, in the Northern Hemisphere.
The box
Four sides, no base. The back wall is taller than the front — a difference of a few inches is enough to create useful slope. Timber, brick or even straw bales all work for the walls.
The lid (light)
A salvaged window is ideal. Hinge it to the back wall so you can prop it open for ventilation and lift it fully for access and harvesting.
Orientation
Slope facing the sun, ideally backed against a south-facing wall that stores and re-radiates heat overnight.
Ventilation
Plan for a prop stick or notched batten so you can vent on mild days. Overheating on a sunny spring afternoon kills more seedlings than frost does.
The 32-page booklet Building a Cold Frame, published by Storey Publishing, gathers several different plans for building a frame along with guidance on using one. If you want a single, considered reference rather than trawling scattered web pages, it's a tidy starting point.
Materials that work
For the walls, untreated or naturally durable timber is the friendly choice if you're growing edibles right up against them. Brick or block gives you superb thermal mass but is far more permanent. Straw bales are a brilliant, cheap, well-insulated temporary option — surprisingly effective and free to compost when they break down. For the lid, a single-glazed window delivers free glazing; a sheet of twin-wall polycarbonate is lighter, safer and better insulating if you're buying new.
DIY Pros
- Genuinely cheap — under $20 to $50 from scrap
- Build to any size your space demands
- Achievable in a single afternoon
- Salvaged windows give free, high-quality glazing
- Easy and cheap to repair or modify later
DIY Cons
- Longevity depends entirely on your materials
- Heavy single-glazed lids can be awkward to lift
- Old painted windows may carry lead paint
- Less tidy than a manufactured kit
- You'll need basic tools and a little confidence
Buyable Cold Frame Kits Worth Knowing
If the kit route appeals, the market is broad — from compact mini lean-tos that bolt against a wall to freestanding growhouses big enough to walk up to. A few brand names crop up repeatedly and are worth recognising: Juwel, Access, Elite and Palram Canopia all build well-regarded frames and growhouses.
In the US, two models give a useful sense of where pricing sits. The Juwel Year-Round Cold-Frame Greenhouse comes in at $186.73, while the larger BioStar 1500 Cold Frame — measuring 59" x 32" x 20" — is $468.95. Those two bracket the territory neatly: a capable year-round frame at the accessible end, and a substantial, generously sized unit for keen growers above it.
Over in the UK, the spread of options is wider still. Traditional flat cold frames range from £249 to £659 depending on size. If you'd rather a mini lean-to greenhouse — useful where you want a bit more height — those run £324 to £949. Freestanding growhouses, the tallest of the bunch, span £425 to £1,275. At the entry point sits the Elite Min E Lite 4x2 at £249, while the largest 3x6 Access Exbury tops the range at £1,275.
| UK Frame Type | Price Range | Best For |
|---|---|---|
| Traditional flat cold frame | £249 – £659 | Classic low-level hardening off and salads |
| Mini lean-to greenhouse | £324 – £949 | Wall-mounted growing with extra headroom |
| Freestanding growhouse | £425 – £1,275 | Larger plant collections and taller crops |
The Elite Min E Lite 4x2 at £249 is the most accessible flat frame in that range, whilst the 3x6 Access Exbury at £1,275 sits at the premium end. Most gardeners will find what they need somewhere in between.
Kit Pros
- Engineered for years of outdoor use
- Quick flat-pack assembly, no tools workshop needed
- Toughened glass or twin-wall polycarbonate glazing
- Neat, consistent finish that suits a tidy plot
- Lean-to and growhouse formats add headroom options
Kit Cons
- Fixed dimensions you can't tweak
- Higher entry cost than scrap-built DIY
- Premium freestanding models climb past £1,000
- Less character than a hand-built frame
What to Grow in a Cold Frame
Here's where a cold frame really earns its keep. The trick is to match your plants to the conditions — a frame is sheltered and warmer than the open ground, but it's still unheated, so cold-tolerant crops are your friends. Reach for the hardy brigade and you'll be picking fresh leaves when neighbours' plots are bare.
Cold frames work best with cold-tolerant crops, and the reliable list reads like a winter grower's wishlist: kale, cabbage, carrots, beets, cauliflower, lettuce and spinach. These shrug off cool conditions and keep ticking over when the warmth is in short supply. For low fruit, strawberries are a natural fit — the frame keeps the worst weather off and brings cropping forward.
Match the crop to the season's job
Think of your cold frame's calendar in three overlapping phases. In late winter and early spring, it's a hardening-off station — sow indoors, then move trays out to the frame to acclimatise. Through autumn and winter, it shifts to overwintering and salad production, keeping spinach and lettuce in fresh growth. And across the cooler shoulder seasons, low crops like salads and strawberries make the most of the trapped warmth.
Growing Tip
Stick to low-growing crops. The whole point of a frame is its compact, ground-hugging space, so anything tall will quickly press against the lid. Salads, spinach, strawberries and low root crops are the sweet spot — leave the tall stuff for the greenhouse or open ground.
How to Use a Cold Frame Through the Year
Owning a cold frame is one thing; using it well is another. The single biggest mistake I see is treating it as "set and forget". A frame needs a little daily attention, especially in spring, because the same trapped warmth that helps your plants can cook them on a bright day.
Hardening off, step by step
When you're moving seedlings from indoor warmth to the great outdoors, the cold frame is your transition zone. Pop the trays inside with the lid closed for the first day or two, then begin propping the lid open during the day and closing it at night. Over a week or so, increase the ventilation until the lid stays open day and night — by then your plants are toughened up and ready for planting out.
Overwintering
For overwintering, the frame protects marginally hardy plants and dormant material from the harshest frost, wind and wet. Keep ventilation ticking over on milder days to prevent stale, damp air and fungal trouble, but close up tight before a cold night. On the very hardest nights, a sheet of fleece or old carpet thrown over the lid adds a useful extra layer of insulation.
Ventilation is the skill that separates a thriving frame from a disappointing one. On a sunny spring day the interior can heat up dramatically, so prop that lid. Always close it again before nightfall if frost threatens.
Siting and Sizing Your Frame
Where you put a cold frame matters as much as how you build or buy it. Because it relies entirely on solar warmth, the position should maximise light and shelter. A south-facing spot against a wall is ideal — the wall blocks cold winds, stores daytime heat and releases it slowly through the night, giving your plants a gentler ride.
Maximise sun
Aim for the sunniest available position, with the sloping lid angled towards the midday sun. Avoid shade from buildings, fences or evergreens.
Shelter from wind
Backing the frame against a wall or hedge cuts wind chill and stops the lid being caught and damaged in gusts.
Good drainage
Because the frame is bottomless and sits on the ground, you want soil that drains freely beneath it — no waterlogging.
Right size for the job
Compact flat frames suit hardening off and salads; lean-tos and growhouses add height for larger collections. Match the footprint to your space and ambitions.
On sizing, be honest about what you'll actually grow. A traditional flat frame in the £249–£659 bracket handles hardening off and low crops superbly. If you find yourself needing more headroom for taller pots or a bigger plant collection, a mini lean-to (£324–£949) or a freestanding growhouse (£425–£1,275) opens up that vertical space — at a higher cost, naturally.
Verdict: Which Route Is Right for You?
The Bottom Line
A cold frame is one of the highest-return, lowest-cost additions you can make to a garden. It hardens off seedlings, overwinters tender plants and keeps low crops cropping, adding roughly 6–8 weeks to each end of your season — all from trapped sunshine and a sloping lid.
If you're handy and have a salvaged window in the shed, build your own: at under $20 to $50 it's almost unbeatable value, and you control every dimension. If you'd rather skip the sawdust and want something tidy and durable that lasts for years, a kit — from accessible models like the Juwel Year-Round at $186.73 up to substantial units like the BioStar 1500 at $468.95, or the broad UK range of flat frames, lean-tos and growhouses — does the job beautifully. Either way, you win.
Who Should Buy (or Build) Which?
The thrifty improviser
You've got an old window and some offcuts. Build your own for under $50 and enjoy the satisfaction — and the customised fit.
The time-poor grower
You want results, not a project. A flat-pack kit assembles fast and lasts for years with toughened glazing.
The seed-starter
If hardening off is your main goal, a compact traditional flat frame is all you need — no need to overspend on height.
The serious collector
Overwintering lots of plants or growing taller crops? Step up to a lean-to or freestanding growhouse for the extra headroom.