How to plan, plant, and harvest winter vegetables under the protection of low tunnels, cold frames, or caterpillar tunnels—with insights from my years gardening in Iowa (Zone 5).

Winter gardening succeeds or fails by the calendar. In cold climates, plants must be established before deep winter arrives—because once day length drops below 10 hours, growth essentially pauses. Under a tunnel, hardy crops won’t grow much in mid-winter, but they will hold in perfect condition for months.

Below is a complete planting calendar, followed by practical tips drawn from my experience gardening through winter in Iowa’s Zone 5 and now gardening year-round in a milder climate.

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Why a Winter Tunnel Planting Calendar Matters

A winter tunnel—whether a simple PVC low tunnel or a more permanent cold frame—creates a microclimate that is:

5–15°F warmer than open air
Protected from wind chill
Shielded from frost and freezing rain
Stable for winter harvesting

But the tunnel can only protect what was planted early enough. A calendar ensures you start hardy vegetables in time to size up before winter.

Winter Tunnel Planting Calendar (Zones 5–8)

(This section fits perfectly with the calendar you already have; the two work as companion pieces.)

July

Sow your long-season hardy crops—carrots, beets, kale, chard, collards.
In Iowa, July sowings gave me the best-sized winter carrots.

August

Plant fall and winter greens—spinach, lettuce, kohlrabi, Asian greens.
This month sets up Thanksgiving harvests.

September

Prime time for spinach, arugula, mache, radishes, and fall transplants.
In Zone 5, mid-September was my last reliable sowing window for winter salads.

October

Sow mache and claytonia; transplant spinach in Zones 6–8.
October plantings are for late winter and early spring harvests.

November

Finish tunnel setup—plastic tight, edges buried, vents ready.
Sow mache in Zones 7–8.

December–January

Growth pauses; harvest stored soil crops (carrots, beets) and leafy greens kept fresh under cover.

February

Begin sowing fast cool crops inside the tunnel again—spinach, radishes, arugula.

March

Transition to spring—spinach, lettuce, and early brassicas thrive under cover.

April

Your winter tunnel becomes a spring tunnel; sow beets, carrots, chard, and lettuces.

My Winter Growing Experience in Iowa (Zone 5)

My years gardening in Iowa taught me how far simple protection can go. Winters were long and cold, but even there, a well-built low tunnel extended the garden into December, January, and sometimes beyond.

Here’s what I learned:

1. Timing Is Everything

In Zone 5, anything sown after mid-September struggled to size up. But those same small seedlings overwintered beautifully and exploded with growth in March.

2. Double Cover Makes a Big Difference

I learned quickly that Zone 5 winters required two layers:

Plastic tunnel
Inner row cover (fleece)

That inner layer protected crops on nights when temperatures plunged below zero.

3. Root Crops Store Perfectly in the Soil

Carrots, beets, and even kohlrabi kept crisp and sweet under the tunnel—no cellar required. Sometimes in January I would brush aside snow, lift the plastic, and pull carrots as if it were October.

4. Snow Is Not the Enemy

Snow insulates. My Iowa tunnels often collapsed under snow loads, but the extra insulation kept everything alive. A quick brush-off restored the tunnel shape.

5. Winter Greens Are Sweeter After Frost

Spinach, mache, tatsoi, and winter lettuces all became dramatically sweeter after repeated freezes.

These lessons continue to shape how I garden now in a much milder climate.

What Crops Do Best in a Winter Tunnel?

Top Performers

Spinach
Mache
Tatsoi
Mizuna
Arugula
Winter lettuces
Kale
Collards
Carrots
Beets
Radishes
Asian greens

Temperamental or Less Suited

Broccoli (great as fall crop, not winter)
Cabbage (needs fall sowing for winter storage)
Cauliflower (too cold-sensitive for mid-winter)

Protection Types That Work Best

1. Standard Low Tunnel

PVC or metal hoops + greenhouse plastic.
Best for Zones 6–8; good for Zone 5 with added inner cover.

2. Double-Cover Low Tunnel

Plastic cover + inner row cover.
Best for Zone 5 or windy, exposed sites.

3. Cold Frame

Wood frame + polycarbonate or storm window lid.
Heats up faster; perfect for late winter and early spring sowing.

4. Caterpillar Tunnel (Mini High Tunnel)

Larger structure with easier access and ventilation.
Great for gardeners growing bigger quantities through winter.

Tips for Success

Water deeply before ground freezes; dry soil freezes faster.
Vent on sunny days to avoid heat buildup.
Keep floating row covers off leaves to prevent freeze contact.
Harvest lightly during deep cold; plants recover better when left mostly intact.

Winter Tunnel Crop Chart (Zones 5–8)

What to plant, when to plant it, and when to harvest under low tunnels, cold frames, or mini caterpillar tunnels.

Crop	Sow/Transplant Window	Zone Notes (5–8)	Days to Maturity	Best Winter Use	Protection Needed
Spinach	Sow Aug–Sept; again Feb–Mar	Zone 5: by Sept 10; Zones 7–8: into Oct	40–55	Winter harvest & overwintered spring growth	Low tunnel + inner row cover in Zone 5
Lettuce (winter types)	Sow Aug–Sept; transplant Sept–Oct	Zone 5: by mid-Sept; Zones 7–8: sow through Oct	40–60	Cut-and-come-again salads	Single cover Zones 7–8; double in Zone 5
Mache (corn salad)	Sow Sept–Nov	Extremely hardy; grows even in low light	60–75	Winter harvest when little else grows	Low tunnel; thrives in cold
Claytonia	Sow Sept–Nov	Best in Zones 6–8, but survives Zone 5	50–60	Winter salads; mild flavor	Single or double cover
Arugula	Sow Aug–Sept; again Feb	Zone 5: by early Sept	30–40	Fast winter green; cut repeatedly	Tunnel + row cover for deep cold
Asian Greens (tatsoi, mizuna, pak choi)	Sow Aug–Sept; some in Oct	Zone 5: sow by Sept 10	30–55	Stir-fries, salads, baby greens	Tunnel + row cover in hard freezes
Kale	Transplant July–Aug	Zone 5: must be established by Sept	50–65	Harvest leaves all winter	Single cover Zones 7–8; double in Zone 5
Collards	Transplant July–Aug	Very hardy; sweetens with frost	60–80	Winter braising green	Tunnel protection only in extreme cold
Chard	Sow or transplant July–Aug	Less hardy; best for fall–early winter	50–65	Fall greens; overwinter in Zones 7–8	Tunnel + inner cover Zone 5
Carrots	Sow July–Aug	Zone 5: sow by Aug 15	70–90	Store in soil all winter	Tunnel + mulch for deep lows
Beets	Sow July–Aug	Harvest fall; hold in winter	55–70	Winter storage in ground	Tunnel + mulch in Zone 5
Radishes	Sow Sept–Oct; Feb–Mar	Zone 5: sow by Sept 25	25–35	Quick winter crunch	Single cover; double only in cold spells
Turnips (small salad types)	Sow Aug–Sept	Zone 5: by early Sept	35–60	Crisp young roots in fall/winter	Tunnel or cold frame
Kohlrabi	Sow July–Aug	Overwinters well if established early	55–70	Crisp storage bulbs	Tunnel + row cover Zone 5
Broccoli (fall only)	Transplant July–Aug	Not winter hardy in tunnels	60–90	Fall harvest before deep cold	Tunnel extends fall season
Cabbage (fall only)	Transplant July–Aug	Harvest before hard freeze	70–100	Fall–early winter storage heads	Tunnel extends late harvest
Green Onions (scallions)	Sow Aug–Sept	Overwinter for early spring	60–80	Winter and early spring use	Minimal cover needed
Garlic (overwinter crop)	Plant Oct	Zones 5–8 all similar	—	Harvest midsummer	Mulch; tunnel not needed

Quick Notes by Crop Type

Best Winter Greens

Spinach
Mache
Claytonia
Tatsoi
Mizuna
Arugula
Winter lettuces

Best Winter Roots

Carrots
Beets
Radishes
Turnips

Best Overwintering Crops

Spinach
Mache
Green onions
Kale
Collards
Garlic (not a tunnel crop but fits timing)

Crops Least Suited for Midwinter

Broccoli
Cauliflower
Cabbage (except hardy storage types)
Chard (unless in Zones 7–8)