Growing vegetables through winter is absolutely possible in zones 5–8—you just need the right protection. Low tunnels and cold frames create a warmer, more stable microclimate that keeps cold-tolerant crops alive and growing even during freezing weather. After years of winter gardening, I’ve found that protected structures are the key to steady greens, crisp roots, and hardy brassicas all the way to spring.

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Below is a detailed guide on how to build, use, and manage low tunnels and cold frames for winter vegetable success.

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My Experience Growing Winter Vegetables in Iowa (Zone 5)

Years before I gardened year-round in Sonoma Valley, I grew winter vegetables in eastern Iowa, Zone 5—where winters are long, cold, and often snowy. Growing through winter there taught me the true value of protection.

Here’s what I learned from those seasons:

1. The Cold Frame Was Essential

I used a simple wooden cold frame topped with an old storm window.

Inside temperatures averaged 10–15°F warmer than outside.
Spinach, lettuce, mâche, and scallions stayed green and harvestable even during single-digit nights.

2. Double-Layer Low Tunnels Provided the Best Insurance

I built low tunnels from EMT conduit and covered them with:

A layer of row cover directly over the crops
A layer of 6-mil greenhouse plastic over the hoops
This double protection prevented the soil from freezing solid—even in January.

3. Snow Was an Unexpected Ally

A layer of snow over the tunnels added extra insulation. Surprisingly, the spinach and kale underneath often looked better in February than in December.

4. Timing Was Everything

In Iowa, I learned to treat winter gardening as fall gardening that continues through winter:

Spinach, kale, and carrots needed to be planted by late August to early September.
Crops had to be nearly full size by the time daylight dipped below 10 hours.

5. Spring Came Early Inside the Cold Frame

By late February, even when daytime highs outdoors hovered in the 30s:

Lettuce began to regrow
Spinach exploded with new leaves
The soil inside the frame warmed enough to sow early spring crops
This jump-started the entire season.

Those Iowa winters taught me that if you can grow winter vegetables in Zone 5, you can succeed anywhere with simple, well-managed protection.

Why Use Protection for Winter Vegetables?

In zones 5–8, winter brings shorter days, freezing nights, and fluctuating temperatures. Cold-hardy vegetables can survive, but they grow more reliably under simple structures that:

Raise temperatures 5–20°F above the outside air
Block wind, which steals heat and moisture
Shield plants from snow and ice
Prevent soil from freezing hard, allowing continued harvest
Extend the season 4–12 weeks at both ends

Best Types of Winter Garden Protection

1. Low Tunnels (Hoop Tunnels)

Best for greens, roots, young brassicas, and full-bed protection.

A low tunnel is a series of hoops covered with fabric or plastic. It creates a simple greenhouse-like shield.

Pros

Inexpensive
Quick to set up
Works on raised or in-ground beds
Easy to vent
Provides 5–20°F of added warmth

Materials

½-inch PVC, EMT conduit, or heavy wire
Row cover fabric (1.0–1.5 oz)
Clear greenhouse plastic (4–6 mil)
Sandbags or soil to anchor edges
Clamps

Management Tips

Vent on sunny days above 45°F
Layer fabric under plastic in zones 5–6
Remove snow to keep hoops from collapsing
Water sparingly—winter soil stays moist

2. Cold Frames

Best for intensive winter production of greens and herbs.

Pros

Warmer than tunnels
Light, bright, and protected
Ideal for winter lettuces, spinach, and hardening-off seedlings

Materials

Wood, block, or straw bale walls
Clear hinged lid (polycarbonate or old windows)
Insulation for the north wall

Management Tips

Prop open the lid on sunny days
Close before sunset to trap heat
Add insulation around the outside
Monitor with a simple thermometer

3. Double Protection for Deep Cold

Recommended for zones 5–6 and cold snaps in zones 7–8.

How to Layer

Row cover directly over plants
Plastic sheeting over hoops

Benefits

Maintains stable nighttime temperatures
Keeps soil unfrozen
Protects even young crops

Best Winter Crops for Protected Growing

Leafy Greens

Spinach, lettuce, arugula, mâche, kale, chard, mustards, tatsoi, claytonia

Root Crops

Carrots, beets, turnips, daikon and winter radishes

Alliums

Scallions, garlic greens, chives

Herbs

Parsley, cilantro, chervil

When to Plant Winter Vegetables (Zones 5–8)

Zones 7–8:

Plant August–October.

Zones 5–6:

Plant August–September.

Crops must reach near-maturity before day length drops below 10 hours.

Examples

Spinach: Aug–Sept
Lettuce: Aug–Sept
Kale/Chard: July–Sept
Carrots: July–Aug
Radishes: Aug–Sept
Beets: Aug–Sept

Final Thoughts

Winter gardening becomes reliable—and even enjoyable—with the help of low tunnels or cold frames. My seasons in Iowa taught me that even in Zone 5, with the right timing and protection, winter vegetables thrive. Once you get the system down, you’ll find yourself harvesting fresh greens and sweet roots long after your neighbors have put their gardens to bed.

Winter Tunnel Checklist (Zones 5–8)

A complete setup and maintenance checklist to keep winter vegetables healthy under low tunnels.

✔ MATERIALS CHECKLIST

Hoops (PVC, EMT, or heavy wire—spaced 3 to 4 feet apart)
Clear greenhouse plastic (4–6 mil) or heavy row cover (1.0–1.5 oz)
Additional inner layer of row cover for extreme cold
Sandbags, soil bags, bricks, or boards for securing edges
Spring clamps or snap clamps
Thermometer (soil and/or air temp)
Mulch (straw, shredded leaves, or compost)
Stakes or rebar to anchor hoop ends (wind protection)

✔ BEFORE INSTALLATION

Prepare and amend soil with compost
Remove summer crops and debris
Plant winter crops early enough (Aug–Sept in Zones 5–6; Aug–Oct in Zones 7–8)
Water deeply before covering
Mulch roots to moderate soil temperature
Install hoops before first frost for convenience
Lay out materials so installation can be done quickly during a cold snap

✔ INSTALLATION

Secure hoops 6–8 inches deep for stability
Drape row cover or plastic over hoops
Anchor sides tightly to prevent wind lift
Seal end walls using sandbags, boards, or clipped fabric
For extra warmth:
- Add a layer of row cover directly on plants
- Use plastic as the outer layer
Add extra insulation (straw bales on north side) if in Zone 5 or windy areas

✔ WEEKLY MAINTENANCE

Vent on sunny days above 45°F to prevent overheating
Close tunnels before sunset to trap afternoon heat
Check for tears or loose edges—repair immediately
Water only when soil is dry 1 inch below the surface
Brush off snow buildup to prevent collapse
Remove leaves or debris that shade the cover
Check thermometer readings and adjust layers as needed

✔ DURING EXTREME COLD (Below 15°F)

Add a second layer of row cover under plastic
Add additional mulch around plant bases
Place water-filled jugs inside to act as heat sinks (optional)
Keep tunnels sealed tightly
Avoid venting unless the sun is very strong
Prioritize insulation over airflow during deep freezes

✔ HARVESTING & MID-WINTER CARE

Harvest lightly and consistently
Avoid exposing plants for long periods during harvest—lift cover, pick, recover
Expect slow growth; plants mostly “hold” in winter
Remove diseased, yellowed, or damaged leaves promptly
Check mulch depth—replenish if it blows away

✔ LATE-WINTER & EARLY SPRING

Begin venting more frequently by late February
Open ends for longer periods on warm days
Remove inner row cover layer when nights stay above 28–30°F
Start sowing early crops (spinach, radishes, lettuces) inside tunnels earlier than outdoors
Watch for aphids in warming weather—ventilation helps prevent buildup