Cold Frames From Salvaged Windows: Fresh Winter Greens Without Power

The morning after an ice storm, when the grid is quiet and the world is silvered and brittle, there’s a small thump of defiance in the garden. A hand lifts a frost-laced window, breath fogging in the cold, and the air beneath spills out warm and green-scented. Spinach leaves snap crisp at 20°F outside because inside that wooden box the sun has pushed the temperature 10–25°F higher—no wires, no humming lights, just glass, wood, and a good seal. That’s the promise of a cold frame built from a salvaged window: fresh calories and vitamins when the supply chain is wobbling and the pantry is heavy on carbs.

I’ve built, broken, and improved these boxes across harsh winters and wind-scoured shoulder seasons—heavy sash from a ReStore, a triple-pane rescue from a renovation dumpster, even a lead-painted relic brought back to useful life with a heat gun and a quart of caution. Cold frames aren’t just “mini-greenhouses.” Done right, they add one to two USDA zones of protection, buffer swings, and turn low winter sun into steady growth without a watt of power.

In this guide, we’ll get specific. You’ll learn how to choose the right salvaged window (weight, glazing type, and safety checks), size the frame to match, and orient it for maximum solar gain and minimal wind load. We’ll cover materials that don’t rot out by March, hinge and prop solutions that vent reliably on a 32°F bluebird day, and insulation tricks that stack the odds at night. You’ll get crop timelines for spinach, mache, claytonia, and kale; watering strategies that avoid mold; condensation control; and a costed build plan you can knock out in an afternoon. We’ll also troubleshoot the usual culprits—slugs, sagging lids, and surprise hard freezes—so your winter greens stay predictable when everything else isn’t.

If you’re ready to turn junk glass into January salads, keep reading.

Salvage Smart: Selecting, Testing, and Decontaminating Old Windows for Safe Food Use

You spot a stack of old windows on a demolition curb—free materials begging to become winter greens. The temptation is real. But the difference between a productive cold frame and a contamination risk starts right here, with smart selection and cleanup. You’re building a food-growing microclimate; treat the lid like kitchen gear that will sit over your salad.

Start With the Right Pane

Size and weight: Aim for manageable lids you can lift one-handed in gloves. A 24×36-inch single-pane weighs roughly 10–15 lb; a 32×48-inch double-pane can push 30–40 lb. If it’s over 30 lb, plan for gas struts or a counterbalance later.
Glass type: Prefer clear, single-pane or tempered storm windows. Tempered glass often has a small corner stamp; with polarized sunglasses you’ll see stress patterns. It’s tougher and safer if broken. Double-pane units work, but fogging indicates a failed seal that cuts light. Avoid tinted or heavily Low-E coated panes (blue/bronze cast) that noticeably reduce solar gain; winter light is precious.
Square and straight: Measure diagonals; a difference greater than 1/8 inch on a 24×36 suggests racking. Lay it on a flat surface—if it rocks, it’s twisted. Warped frames leak heat and strain hinges.
Frame material: Aluminum and vinyl are easier to decontaminate than old softwood. If wood is punky, deeply cracked, or flaking badly, keep walking—you’ll spend more time sealing rot than growing greens.

Screen for Hazards

Lead paint: Any pre-1978 painted sash is suspect. Use EPA-recognized lead test swabs (e.g., 3M LeadCheck) on painted wood and glazing putty. If the test is positive and paint is chipping, don’t sand; either skip it or plan to encapsulate thoroughly.
Old glazing compounds: Some vintage putties contain lead and other nasties. If they’re brittle and crumbling, assume hazardous dust if disturbed.
Mold and grime: Musty odor, black/gray fuzz, or greasy residues need more than a quick Windex pass. Food is growing inches away; treat residues like kitchen contaminants.
Unknown residue: If it came from a shop or industrial site, err on the side of caution—choose a different pane. The risk-to-reward ratio isn’t there.

Decontamination That Actually Works

PPE and setup: Work outdoors on a tarp. Wear nitrile gloves and a P100 or N100 respirator if lead is suspected. Lightly mist surfaces to keep dust down.
Dry capture first: HEPA-vac seams, sash joints, and corners. Avoid regular shop vacs—they can aerosolize fine dust.
Wet cleaning: Use a strong detergent solution (or TSP substitute) on wood and aluminum. Scrub, rinse, and change water frequently. Avoid dry sanding. If loose paint must come off, use wet scraping only.
Encapsulation: After drying 24 hours, seal wood with two coats of exterior acrylic paint or marine varnish, focusing on the underside that will face the greens. This locks in residues and stops future flaking.
Glass cleaning: Razor-scrape paint specks, then wash with hot water and detergent. Final wipe with 70% isopropyl or vinegar solution for a squeaky finish.
Extra barrier: For peace of mind, staple 4–6 mil clear poly sheeting to the underside of the sash as a drip barrier. Keep it taut so condensation sheds instead of dripping.

Troubleshooting and Common Mistakes

Don’t dry-sand suspect paint—ever. It spreads lead dust.
Fogged double-panes still “work,” but they’re heavier and dimmer. If you must use one, consider propping it slightly to vent humidity.
Skipping the seal coat invites future flaking into your greens.
Ignoring weight leads to smashed seedlings and smashed fingers. Plan hinges and lifts accordingly.

Key takeaway: Choose windows that are cleanable, structurally sound, and safe around food. Test for hazards, decontaminate with wet methods, and encapsulate or add a barrier where needed. With a trustworthy lid sorted, we can size and orient the frame to capture winter sun without losing heat.

Design That Captures Sun: Orientation, Pitch, and Frame Dimensions for Your Latitude

Picture a clear January noon at 42°N. The sun hovers just above the horizon, your beds are crusted with frost, and the difference between limp spinach and a living salad is whether your cold frame is aimed and angled for that brief, low arc of light. Get the geometry right, and the frame becomes a passive solar collector that warms and brightens plants when they need it most.

Orient for Winter Sun

Face the glazing true south in the Northern Hemisphere (true north if you’re south of the equator). Not magnetic south—check your local magnetic declination and correct your compass, or use a phone compass app set to “true.” Run the long dimension of the frame east–west so the slope looks south and the entire bed gets even exposure from morning through afternoon.

Why it matters: In winter, useful light is scarce and low. A south-facing slope reduces reflection losses and pulls in the warmest rays around midday. Site matters, too. Avoid winter shade from fences and buildings by checking shadow length: noon shadow ≈ object height ÷ tan(winter sun altitude). At 40°N on the solstice, altitude is about 26.5°. A 6-foot fence will throw roughly a 12-foot shadow at noon (6 ÷ tan 26.5° ≈ 12), so keep your frame well clear of that zone.

Set the Pitch for Your Latitude

The “ideal” optical tilt for winter is roughly latitude + 10–15°, which points the glazing more perpendicular to low sun. But salvaged windows and comfort working height impose limits. Use these practical targets:

30–40° slope for 35–45°N
40–55° slope for 45–55°N
20–30° slope near 30°N

Translate slope into lumber: height difference = depth × tan(slope). Example: with a 36-inch-deep lid at 35°, tan 35° ≈ 0.70, so the back should be about 25 inches taller than the front. A front rail at 8 inches and a back at 33 inches is workable and sheds snow. Push to 45° and that 36-inch depth needs a 36-inch height difference—great for light, awkward to build. Compromise is normal. If your slope is shallower than ideal, compensate by situating the frame in the sunniest microclimate you have and by keeping the interior volume tight so it warms quickly.

Why it matters: Steeper slopes reduce glare losses when the sun is low and shed snow instead of shading plants. Too shallow a lid reflects light away and collects slush, but a too-steep lid becomes tall, wind-prone, and cumbersome to vent.

Size the Frame to the Window—and Your Arms

Start with the glass you have. Common sash sizes are 24×36, 28×32, and 30×48 inches. Build the box to match, with the hinge along the north edge so the lid faces south. Keep depth (south lip to north wall) to 24–36 inches if you’ll access from one side; go up to 48 inches only if you can reach from both sides. Front height of 6–10 inches and back height of 16–24 inches fit most greens and maintain a small, heatable air volume. Overhang the glass 1/2–1 inch at the front for a drip edge.

Common mistakes and fixes:
– Aiming “south-ish.” At high latitudes, 10° off costs real light; correct to true south.
– Oversizing depth. Deep frames self-shade; keep them within reach and within your chosen slope.
– Ignoring local shade. Map winter shadows before you build.
– Hinging on the wrong side. Hinge on the north so the lid doesn’t cast its own shadow.

Key takeaway: Let latitude set your tilt, but let your window and working reality set the final geometry. Face true south, choose a slope that sheds snow and suits your site, and size the box so you can actually work it. Next, we’ll turn that salvaged sash into a weather-tight lid that holds heat without smothering your greens.

Build a Bombproof Box: Framing, Hinges, Gaskets, and Drainage That Outlast Winter

Picture the first nor’easter of the season rolling in: wet snow, gusting 30 mph, and temperatures dropping fast. A salvaged window can keep greens alive through that punch—if the box beneath it is built like it means business. This is the moment your framing, hinges, gaskets, and drainage either work together…or the glass heaves, the lid rattles, and your soil turns to soup. Build it once, build it tough.

Framing for Load and Heat Retention

Start with rot-resistant lumber where it touches soil. Ground-contact treated pine or cedar is your friend; at minimum, seal all end grain with copper naphthenate. For a typical 24×48-inch sash, aim for a back wall 16–18 inches high and a front wall 10–12 inches high—about a 5–10° slope to shed water and catch winter sun without creating a sail in the wind. Use 2×8 at the back, 2×6 at the front, and 2×6 sides.

Join corners with exterior construction adhesive and 3-inch ceramic-coated deck screws, two per joint, staggered. Add 6×6-inch 3/4-inch plywood gussets inside each corner for racking resistance. On the inside top edge, install a 1×2 “seat” for the sash to land on; this creates a lip that supports the glass uniformly. Leave a 1/8-inch gap around the sash perimeter to account for swelling and prevent binding in freeze-thaw cycles.

Why this matters: beefy framing resists snow load and lateral wind pressure, while the slope manages meltwater and radiant heat capture. The continuous seat keeps stress off fragile sash joints.

Pro tip: If your window is heavy, through-bolt a cross-brace (a 1×3) under the sash with fender washers to stiffen it. Old muntins aren’t designed for snow.

Hinges That Don’t Quit

Use a stainless or brass continuous (piano) hinge along the back edge. It spreads load across the full width, so the sash doesn’t rack and split. Pre-drill and use #8 x 3/4-inch stainless screws into the sash, and 1-inch screws into the box. If the sash rail is thin, through-bolt with machine screws and finish washers.

Add two adjustable toggle latches at the front corners to clamp the lid tight. Install a chain stay or a notched prop stick inside to prevent the lid from flipping in gusts. A dab of exterior caulk over the hinge line keeps meltwater from wicking into the joint.

Common mistake: using two small butt hinges. They twist under snow and wind, loosening fasteners and telegraphing stress into the glass.

Seal the Edges—Smart Gaskets

Heat leaks at the perimeter make more difference than glass R-value. Apply a 3/8-inch EPDM bulb seal or high-density closed-cell foam tape on the sash seat. Aim for 25–50% compression when latched. In deep cold, adhesive fails—mechanically retain the gasket with a thin lath strip and stainless staples.

Add an aluminum drip cap under the front edge of the sash to kick meltwater forward. Skip felt weatherstrip; it soaks and freezes.

Troubleshooting: If the lid rocks on high points, plane the seat or double up gasket at low spots. Listen on a windy day—whistles mean leaks.

Drainage and Base Work That Lasts

Set the box on a 3–4-inch bed of 3/4-inch crushed stone (not pea gravel), extending 3 inches beyond the perimeter. On the uphill side, dig a shallow trench (6 inches deep), fill with gravel, and pitch it away at 1/8 inch per foot. If your site is wet, lay a 4-inch perforated pipe with sock and daylight it downslope. Keep the bottom open to native soil for root access; line inside faces with HDPE sheet up to soil line to slow rot without trapping moisture.

Why: Frozen wet soil heaves and warps frames. Stone decouples the box from frost heave, and drainage keeps microbes happy while roots stay oxygenated.

Common mistake: setting wood directly on soil. It wicks moisture, swells, and twists hinges out of alignment in a single season.

Key takeaways: build with a sloped, braced frame; use a continuous hinge and proper latches; seal the lid with compressible EPDM; and prioritize drainage under and around the box. With the shell bombproofed, you’re ready for the next critical piece: controlling temperature and airflow without babysitting.

Stacking Passive Heat: Insulation, Thermal Mass, and Snow Strategy Without Electricity

Picture a clear, 18°F morning after a radiative freeze. Your salvaged-window cold frame has a skim of frost inside the glass, but the soil under your spinach is still soft, and the leaves haven’t burned. That didn’t happen by accident. In winter, you’re not “heating” so much as slowing heat loss and smoothing temperature swings. Stacking passive strategies—insulation, thermal mass, and smart snow management—lets a simple box act like a snug microclimate without a single watt.

Wrap the Box: Insulation That Actually Matters

Cold frames leak heat through their sides, bottom, and glazing. You can’t change the sun, but you can control conduction and convection.

Perimeter insulation: Line the exterior walls with 2-inch polyiso foam (R-12) or EPS (R-8). Better yet, bury a vertical “curtain” of foam 8–12 inches deep around the box to reduce lateral frost creeping into your bed. In windy sites, add a 12–18-inch foam “skirt” on the surface, covered with soil or mulch, to break the wind chill at ground level.
Straw bales: If foam isn’t your style, stack 2-string straw bales on the windward and north sides. A typical 18-inch bale is roughly R-25–R-30 and doubles as a windbreak. Keep them 1–2 inches off the soil with bricks to reduce wicking and rot.
Night covers: A removable insulated quilt (an old moving blanket with a layer of reflective bubble wrap works) cuts radiative losses through the glass. Lay it on at dusk when the forecast shows clear skies; remove by mid-morning to avoid shade-induced dampness.

Why it works: You’re slowing the three thieves—conduction into frozen ground, convection from wind, and radiation to the night sky. The result is fewer catastrophic drops and less plant stress.

Troubleshooting: Don’t sandwich organic insulation tight to bare wood; trapped moisture invites rot. If you use foam, shield it with scrap plywood where the sun hits—it degrades under UV. Check for rodent burrows in straw weekly.

Add a Flywheel: Thermal Mass That Smooths Swings

Water is your friend. One gallon weighs 8.34 lb and stores 8.34 BTU per degree F. A single 5-gallon jug, warmed 30°F on a sunny day, banks roughly 1,250 BTU for the night.

Placement: Set three to six 1–5 gallon, dark-painted jugs along the north wall where they won’t shade plants. Black or deep blue absorbs best; keep lids on to prevent humidity spikes.
Floor mass: Replace exposed soil paths with dark pavers or bricks. They add mass and keep muddy boots at bay. A 2-inch slab bed under the frame also reduces heat loss into deep frost.
Air gap trick: Add an inner “storm window” by stretching clear poly or a floating row cover (0.5–0.9 oz/yd²) 1–2 inches below the glass. The still air layer adds roughly R-1 while letting light in; it also reduces nighttime radiative cooling onto leaves.

Why it works: Mass releases stored heat when the air cools, flattening the curve between a 45°F solar noon and a 12°F predawn. Plants hate roller coasters; mass makes the ride gentle.

Troubleshooting: Overdo mass and the frame warms slower on marginal days. Watch for jugs freezing solid during prolonged cold snaps; leave a 10% air space in containers to prevent splitting.

Use Winter’s Blanket: Snow As Insulation and Windbreak

Snow is an insulator if you manage it. A 6-inch drift against the north side creates a dense windbreak and buffers cold air pooling.

Clear glazing, keep skirts: After storms, push snow off the glass with a soft broom—never a shovel—to protect old panes. Leave 3–6 inches piled along the sides as an insulating berm.
Roof loads: Salvaged windows vary. If your lid is flat or shallow-pitched (<15°), add a central prop or a lightweight ridge stick before a heavy, wet snowfall. Better yet, build lids with a 20–30° pitch so snow sheds and sun enters at a better winter angle.

Why it works: You maintain light (the real “heat engine”) while harnessing snow’s R-value at the edges and breaking wind scour.

Troubleshooting: Don’t seal the frame in with snow on all sides; you still need to vent on sunny days. Watch melt-refreeze cycles—ice at the sill can pry frames apart. Sprinkle a handful of sand, not salt.

Key takeaways: Slow losses with perimeter insulation, bank daytime BTUs with water and masonry, and let snow work for you while keeping glass clear. Next, we’ll dial in ventilation and moisture control so your greens don’t cook on a bright January afternoon.

Greens That Thrive in Cold: Soil Mix, Sowing Dates, and Spacing for Reliable Harvests

A white crust of frost glazed the pasture, but when you crack the salvaged window and see glossy leaves waiting, you understand why cold frames are worth the fuss. The trick isn’t magic—it’s matching the right greens to the right soil, sowing windows, and spacing so plants hit stride before deep winter slows everything down.

Soil That Doesn’t Sulk in Winter

Cold-frame soil needs to drain fast yet hold nutrients. Cold roots hate saturation; waterlogged beds invite rot and slugs. Aim for a loose, living mix:
– Base: 50% quality, finished compost + 30% topsoil + 20% coarse mineral (coarse sand or perlite). In heavy clay, swap sand for 1/4″ screened gravel for better drainage.
– Per 10 sq ft, work in 1–2 inches of compost and 1 cup of a balanced organic fertilizer (around 4-4-4). If pH is below 6.2, add garden lime at 3–5 lbs per 100 sq ft to hit 6.5–7.0, where most winter greens thrive.
– Pre-warm the bed: two sunny days with the sash closed on a dark compost surface tacks on a few degrees, speeding germination.

Why this mix? Winter growth is slow; you won’t be side-dressing much. Nutrient-dense, well-drained soil produces sturdy leaves with less frost damage. Overly rich, soggy beds push soft, sappy growth that blackens at 25°F.

Common mistake: peat-heavy seed-starting blends used as full-bed soil. They compact and stay cold-wet. If that’s all you have, lighten aggressively with perlite and coarse sand.

Sowing Dates That Beat the Short-Day Slowdown

Your goal is to have plants nearly full-sized by the “Persephone period” (roughly when day length dips below 10 hours). After that, they hold—and you harvest—rather than grow fast.

Zone 5: Sow Aug 20–Sep 15 for main crops; last quick salad sowing by Sep 25.
Zone 6: Sep 1–Sep 25; last quick sowing by Oct 1.
Zone 7: Sep 15–Oct 10; last quick sowing by Oct 15.

Spinach likes cool soil; pre-chill seed in the fridge for a week or pre-sprout 24–36 hours for even stands. If you miss the dates, start seedlings indoors under modest light and transplant at 3–4 weeks to catch up.

Troubleshooting: Patchy germination? Soil’s too warm for spinach (over 75°F) or too dry under a hot lid. Vent and mist lightly twice daily until emergence.

Spacing That Balances Yield and Airflow

Tight spacing boosts yield per square foot, but winter humidity punishes overcrowding. A workable grid:

Spinach: rows 6–8″ apart, thin to 4–5″ in-row for cut-and-come-again; 6″ for full leaves.
Mâche (corn salad): broadcast thickly and thin to 1–2″; or 3″ grid for tidy rosettes.
Claytonia (miner’s lettuce): 4″ grid; it sprawls modestly.
Arugula: rows 6″ apart, thin to 3–4″.
Mizuna/Tatsoi: 6–8″ for continual cuts; 8–10″ for heads.
Baby kale (Vates, Winterbor, Red Russian): 6–8″ for leaf harvest; 12″ for small heads.

Plan harvest by maturity: arugula and mizuna in 25–35 days; spinach 35–50; mâche 50–60 but cold-tolerant to the teens. Mix fast and slow varieties to keep bowls full while the slowpokes bulk up.

Common mistake: carpet sowing everything. It looks lush, then mildew sneaks in. Keep a finger-width of bare soil visible after thinning; think airflow first.

Key takeaway: Build a quick-draining, nutrient-rich bed, sow early enough to beat the short days, and give each plant just enough elbow room to stay dry and durable. Next, we’ll dial in low-tech care—venting, watering, and freeze protection—to keep those greens cruising through the cold.

Run It Like a Pro: Venting, Monitoring, Troubleshooting, and Midwinter Maintenance

The first sunny day after a storm is when cold frames prove their worth—or burn your spinach. I’ve watched a January sun bump a sealed frame from 28°F at dawn to 85°F by lunch while the ambient air stayed below freezing. Managing that swing is the difference between crisp, sweet leaves and cooked salad. Here’s how to run your salvaged-window frame like a pro all winter long.

Smart Venting: Prevent the Solar Oven Effect

Trigger points: For hardy greens (spinach, mâche, kale, mizuna), start cracking the lid when inside air hits 40–45°F. At 50–55°F in sun, prop open 4–6 inches. Over 60°F with strong sun? Give it 8–12 inches, or even full-open if wind is light and you can supervise. The goal is a steady 40–60°F daytime band; above 70°F risks stress and aphids later.
How to control reliably: Use a notched prop stick (mark 1, 2, 4, 6, 8 inches) or adjustable sash locks. A bungee from the lid handle to a ground screw prevents gusts from flipping a heavy sash. Automatic wax-cylinder vent openers can be adapted—mount inside with a bracket—but test their lift against your window’s weight.
Why it matters: Fluctuations don’t just wilt leaves; repeated overheating followed by a hard freeze triggers tip burn, bolting in Asian greens, and encourages mildew. Consistent venting keeps stomata happy and sugars building.

Common mistakes:
– “Set and forget” on sunny-cold days—frames cook fast by late morning.
– Venting too wide in wind—leaves desiccate; use partial openings and windward vents.
– Opening late afternoon—dumping heat just before nightfall.

Monitoring That Gives You an Edge

Minimum/maximum thermometer: A $15 analog or digital min/max hung at plant height tells you what happened when you weren’t there. Aim for night lows above 25°F at canopy level; if forecasts threaten lower, add an inner row cover.
Soil thermometer: Roots are the engine. If soil holds 34–40°F at 2 inches, plants keep ticking. Below 32°F for days, growth stalls; add mulch or thermal mass (dark water jugs).
Quick log: Note morning low, noon high, vent gap, and weather. Three lines a day builds patterns you can trust.

Watering in winter is sparse but strategic: Feel 2 inches down; water when it’s dry to your second knuckle. As a rule, 0.5 gallon per 4 square feet per week in cold, sunny weather; half that in cloudy stretches. Always water late morning with lukewarm water so foliage dries before night.

Troubleshooting: Read the Signals

Wilting at noon on sunny days: It’s heat, not drought. Vent earlier or wider. If leaves perk by evening, you nailed it.
Leaf edge burn after a clear snap: Add an inner row cover (0.5–0.9 oz fabric) draped over hoops. It adds 2–4°F of plant-level protection and blunts radiative losses.
Condensation dripping and mildew: You need more airflow. Space plants, vent daily, and wipe the sash underside weekly with a microfiber cloth. A light sand mulch around stems reduces spore splash.
Aphids in February: Classic post-overheat problem. Blast with a water spray on a mild day, then follow with insecticidal soap. Keep days under 65°F to prevent rebounds.
Mice or slugs: Seal gaps with 1/4-inch hardware cloth. For slugs, beer traps or a nighttime headlamp hunt after thaws.

Midwinter Maintenance: Keep It Moving

Snow and ice: Brush snow off with a soft broom; never bang glass. If the lid is iced shut, pour lukewarm water along the edge; avoid salt—it wrecks wood and soil.
Hinges and seals: Midseason, hit hinges with dry lube and check screws. Replace tired weatherstrip with adhesive foam in 10 minutes; it pays back every night.
Repack insulation: Straw or leaves along the frame perimeter settle. Top them off to curb soil-edge freezing.
Thermal mass: If your min/max shows low 20s inside, add two black 1-gallon jugs of water per 4 square feet. They’ll bank a few degrees overnight.

Key takeaway: Run the frame, don’t let it run you. Vent by numbers, confirm with instruments, and fix small issues before they snowball. Do that, and your salvaged sash will deliver crisp greens through the bleakest stretch, with fewer surprises and a lot more salads.

When you lift a frost-rimed sash in January and warm air rushes out, you’ll know the system is working: safe salvage, smart geometry, durable joinery, and passive heat all doing quiet, reliable work. The through-line is simple—treat a cold frame like field gear. Vet your materials, design for your latitude and wind, build it to shed water and hold a seal, then run it with discipline.

Your next move is straightforward. This week: source two or three candidate windows, test for lead, and decontaminate; reject anything that fails and seal suspect paint edges. Walk your site at first light and late afternoon to mark winter sun and wind; sketch a frame footprint with lid pitch that won’t shade itself. Assemble materials—rot-resistant lumber, continuous hinges, weatherstripping, gravel for drainage, rigid foam, and a couple of water jugs or bricks for thermal mass. Build one “pilot” frame, not three, and instrument it with a min/max thermometer and a soil probe so you learn before scaling. Back-plan sowing dates for cold-hardy greens from your first hard frost; keep a simple log of temps, venting times, and growth.

Common failure points are almost always management: vent too late, overwater, ignore condensation, let snow load linger. Set a weekly maintenance block, keep a broom and prop stick by the frame, and have a backup row cover ready for arctic snaps.

Do this, and you’ll eat crisp leaves while the world is white—no wires, no noise, just a pocket of resilience you built from scrap and sun.

Cold Frames From Salvaged Windows: Fresh Winter Greens Without Power