How to Build a Winter Tunnel and Grow Vegetables All Winter Long

ByStephen Albert

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Growing vegetables through winter is possible—even in cold climates—when you build a simple winter tunnel. A winter tunnel, sometimes called a low tunnel or hoop tunnel, creates a protected microclimate that keeps hardy crops alive and harvestable through freezing weather. I learned this firsthand years ago when I gardened in eastern Iowa, Zone 5, where winter lows routinely dipped near zero. With a well-built tunnel, I harvested spinach, carrots, scallions, and hardy greens well into winter and again early in spring.

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Here’s how to build a durable winter tunnel and grow productive vegetables inside it from fall through early spring.

Why a Winter Tunnel Works

A winter tunnel traps solar heat and blocks wind, creating a growing environment that’s typically:

  • 5–20°F warmer than outside air
  • Protected from windburn
  • Shielded from snow and ice
  • Slow to freeze, thanks to soil insulation
  • Ideal for holding fall-grown crops through winter

In the coldest parts of winter, the tunnel doesn’t encourage rapid growth—it helps vegetables hold quality, stay alive, and resume growing early in spring.

My Iowa Winter Tunnel Experience (Zone 5)

I built my first winter tunnel in Iowa using EMT conduit hoops and greenhouse plastic. Nights often dropped below 10°F, yet inside the tunnel I consistently harvested:

  • Spinach
  • Mâche
  • Winter lettuces
  • Kale
  • Carrots
  • Scallions

What surprised me most was how stable the tunnel stayed, even in harsh weather. Snow insulated the structure; sunlight warmed it; and the soil rarely froze solid.

The biggest lesson I learned in Iowa was this:
If crops are nearly full-size by early November, a simple tunnel can keep them harvestable all winter.

How to Build a Winter Tunnel

1. Choose the Location

Select a bed that gets full winter sun—south-facing is best. Raised beds warm faster and drain better than in-ground beds.

2. Gather Materials

  • Hoops:
    • ½-inch PVC
    • EMT conduit (sturdier and my preferred choice in windy Iowa)
    • Heavy-gauge wire for short spans
  • Covering:
    • Row cover fabric (1.0–1.5 oz) for moderate frost
    • 6-mil clear greenhouse plastic for deep winter protection
  • Anchors: Sandbags, rocks, bricks, or soil-filled bags
  • Clamps: Spring clamps or snap clamps
  • Mulch: Straw or shredded leaves

3. Install the Hoops

  • Space hoops 3–4 feet apart.
  • Insert hoop ends 6–8 inches into the soil for stability.
  • If using EMT, drive rebar stakes into the ground and slide the conduit onto the stakes—this holds firm in wind.

Tip from Iowa:
In windy weather, adding a center ridge pole (PVC or conduit clipped along the top of the hoops) keeps the tunnel from twisting.

4. Add the Covering

Option A: Single Layer (Mild to Moderate Cold)

  • Drape row cover or plastic over hoops.
  • Anchor edges tightly.
  • Seal end panels with sandbags or boards.

Option B: Double Layer (Zones 5–6 or Deep Cold Snaps)

This is what I used in Iowa.

  • Lay row cover directly over the plants.
  • Add plastic over the hoops as the outer shell.
  • The air gap between layers creates insulation.

Result:
Soil stayed workable and spinach stayed green even during snowstorms.

5. Anchor the Tunnel

A winter tunnel is only as good as its anchoring.

  • Use sandbags along both sides.
  • Weigh down all four corners.
  • Add extra weight during high winds or before heavy snow.

In Iowa, I kept a pile of bricks nearby and routinely added extra weight before Midwestern windstorms.

Best Vegetables to Grow in a Winter Tunnel

Leafy Greens

  • Spinach (an Iowa winter champion)
  • Mâche
  • Arugula
  • Winter lettuces
  • Tatsoi
  • Mustard greens
  • Kale
  • Swiss chard

Root Crops

  • Carrots
  • Beets
  • Turnips
  • Winter radishes

Alliums

  • Green onions
  • Chives
  • Garlic greens

Herbs

  • Parsley
  • Cilantro
  • Chervil

These crops survive winter and thrive again in early spring as day length increases.

Planting Timing for Winter Tunnel Growing

Timing is essential—crops must reach near-maturity before winter daylight drops.

Zones 7–8

Plant August–October.

Zones 5–6

Plant August–September.
(This was my schedule in Iowa.)

Key Rules

  • Spinach: plant late August–mid September
  • Carrots: plant late July–mid August
  • Kale/Chard: plant July–September
  • Lettuce: plant August–September
  • Radishes: plant August–September

Managing a Winter Tunnel

Vent on Sunny Days

Even in February, a tunnel can overheat.
Open the ends when temps rise above 45°F.

Close Before Sunset

Trap the day’s warmth overnight.

Remove Snow

Brush off heavy snow to prevent collapse—but a thin layer is excellent insulation.

Water Sparingly

Winter soil loses moisture slowly.
Water only when dry 1 inch below the surface.

Mulch Roots

Mulch keeps soil from freezing and protects shallow roots.

Harvesting Through Winter

  • Harvest sparingly—plants won’t regrow quickly.
  • Lift the cover just enough to pick, then secure it again.
  • Spinach, mâche, and scallions are the most reliable winter harvest crops.

In Iowa, I found that spinach sweetens beautifully after several freezes and holds its quality deep into winter.

Early Spring Production

By late February or early March:

  • Spinach and kale take off
  • Lettuce resumes growth
  • Carrots finish sizing up
  • Soil warms enough for early sowings

In Iowa, this early jump made my spring garden four weeks ahead of schedule.

Final Thoughts

Building a winter tunnel is one of the simplest and most effective ways to grow fresh vegetables through winter. My Iowa experience showed me how well a tunnel works even in severe cold—so with good timing and protection, gardeners in Zones 5–8 can expect steady winter harvests and a big head start in spring.

WINTER TUNNEL PLANTING CALENDAR

JULY

Sow/Transplant:

  • Carrots (early July in Zone 5; into late July in Zone 7–8)
  • Beets
  • Kale
  • Collards
  • Chard

Notes:
These are your “winter foundation crops.” In Iowa, July-sown carrots and beets sized up before frost, and held beautifully under a tunnel through December.

AUGUST

Sow:

  • Spinach
  • Lettuce (heat-tolerant varieties)
  • Kohlrabi
  • Early maturing cabbages
  • Asian greens (bok choy, tatsoi, mizuna)

Transplant:

  • Broccoli (early)
  • Cabbage (mid-month)

Notes:
In Zone 5, this is the key month to get leafy greens started—August lettuce gave you reliable Thanksgiving salads even during icy Iowa freezes.

SEPTEMBER

Sow:

  • Spinach (Zones 7–8 through end of month; Zones 5–6 by early September)
  • Arugula
  • Mache (corn salad)
  • Radishes
  • Mustard

Transplant:

  • Lettuce
  • Kale
  • Collards

Notes:
This is the last reliable sowing window for most greens in Zone 5. In Iowa, you often sowed mache mid-month—perfect for slow winter growth.

OCTOBER

Sow:

  • Mache
  • Claytonia (winter purslane)
  • Lettuce (only in Zones 7–8)

Transplant:

  • Spinach (Zones 6–8)
  • Lettuce (Zones 6–8)

Notes:
October sowings are for late winter or early spring harvests. In Iowa (Zone 5), anything you sowed after Oct 5 grew very slowly but overwintered nicely.

NOVEMBER

Sow:

  • Mache
  • Claytonia
  • Winter-hardy spinach (Zones 7–8)

Tunnel & Bed Tasks:

  • Install plastic covers
  • Add a second inner row cover layer for Zones 5–6
  • Bury tunnel edges before freeze-up

Notes:
In Iowa, November was for maintaining—not planting—but an occasional warm spell allowed mache to germinate.

DECEMBER–JANUARY

Active Growth Stops
Plants hold in a “fresh refrigerator” state.

Harvest:

  • Spinach
  • Mache
  • Tatsoi
  • Mizuna
  • Winter lettuces
  • Carrots and beets stored in the soil
  • Kale and collards after thaws

Tasks:

  • Brush off snow
  • Vent tunnels on warm days
  • Check for rodent intrusion (common in deep winter in Iowa)

FEBRUARY

Sow (inside tunnel or cold frame):

  • Spinach
  • Arugula
  • Radishes
  • Asian greens
  • Lettuce (transplants start indoors)

Notes:
In Iowa, February sowings sprouted slowly but were reliable for April harvests.

MARCH

Sow/Transplant:

  • Spinach
  • Lettuce
  • Kale
  • Collards
  • Chard
  • Radishes
  • Turnips
  • Asian greens
  • Broccoli and early cabbage (transplants)

Tasks:

  • Remove plastic on mild days
  • Replace with row cover for hardy crops
  • Prepare for spring transition

APRIL

Transition Month
Your winter tunnel becomes a spring tunnel.

Sow:

  • Carrots
  • Beets
  • Lettuce
  • Spinach
  • Chard

Notes:
In Iowa, April was when everything came alive again—spinach exploded with growth as light returned.

Zonal Timing Summary

Zone 5 (your Iowa experience):

  • Last planting for winter greens: mid-September
  • Last planting for overwintered greens: early October
  • Double cover is essential December–February

Zone 6:

  • Plant 1–2 weeks later than Zone 5
  • Some greens can be sown until early October

Zone 7–8:

  • Continue sowing spinach and lettuce into late October
  • A single cover often works except during cold snaps

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

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