What Temperature Do Winter Crops Need for Row Covers

Last Updated on October 19, 2026 by D. Ruddy

Simply put, most winter crops need row covers when temperatures drop below 28°F (-2°C) for light frost protection or 20°F (-7°C) for heavy-duty frost. Lightweight covers add 2-4°F, while thick covers can protect down to 10°F (-12°C).

Key Takeaways

• Winter crops need row covers when temperatures fall below 28°F (-2°C) for sensitive plants or 20°F (-7°C) for hardy varieties.
• Row cover temperature ratings vary by thickness: lightweight (2-4°F), medium (4-6°F), and heavy (8-12°F).
• What temperature do winter crops need depends on the plant type—kale tolerates 10°F (-12°C), while lettuce needs above 25°F (-4°C).
• Remove covers on warm days (above 50°F/10°C) to prevent overheating and allow pollination.
• Secure covers tightly to block wind and pests while allowing airflow.

What Temperature Do Winter Crops Need for Row Covers?

Row covers act as a thermal blanket, trapping heat from the soil and sun to shield plants from cold snaps. The exact temperature winter crops need row covers depends on the crop’s hardiness and the cover’s thickness. Most gardeners use covers when nighttime temperatures dip below 28°F (-2°C), but some cold-hardy plants like spinach or Brussels sprouts can handle temperatures as low as 15°F (-9°C) with heavy protection.

Here’s a quick breakdown of temperature thresholds for common winter crops:

As a rule of thumb, row covers can add 4-8°F (2-4°C) of warmth, but heavyweight frost blankets may provide up to 12°F (6°C) of protection. Always check the manufacturer’s rating for your specific cover.

Tip: Use a soil thermometer to monitor temperatures at plant level. Row covers work best when they’re in direct contact with the soil or supported by hoops to prevent sagging from snow or wind.

How Do Row Covers Work to Protect Winter Crops?

Row covers, also called frost blankets or garden fabric, create a microclimate around plants. They work through three main mechanisms:

1. Heat Retention: The fabric traps radiant heat from the soil, which warms the air directly around the plants. Soil releases heat absorbed during the day, and the cover prevents it from escaping into the cold night air.
2. Wind Protection: Even a light breeze can cause wind chill, damaging plant tissues. Row covers act as a barrier, reducing wind speed and preventing desiccation.
3. Frost Prevention: The fabric prevents ice crystals from forming directly on plant leaves. Instead, frost forms on the cover’s surface, leaving the plants underneath unharmed.

According to the University of Massachusetts Extension, row covers can extend the growing season by 4-6 weeks in fall and spring and allow year-round harvests in mild winter climates. However, their effectiveness depends on proper installation and weight selection.

Here’s how different weights perform in terms of what temperature do winter crops need:

For most winter crops, medium-weight covers (1.0 oz/yd²) offer the best balance between protection and light transmission. Heavy covers block too much sunlight, which can stunt plant growth on sunny winter days.

What Are the Best Winter Crops for Row Covers?

Not all vegetables need the same level of protection. Some crops are naturally cold-hardy and can survive brief freezes without covers, while others require consistent warmth. The temperature winter crops need for row covers varies significantly by species.

Most Cold-Tolerant Crops (Can Handle 10-15°F / -12 to -9°C Without Covers)

• Kale: One of the hardiest winter greens, kale can survive temperatures as low as 10°F (-12°C) without protection. With a heavy row cover, it can tolerate dips to -5°F (-21°C).
• Brussels Sprouts: These thrive in cold weather, with flavors sweeter after a frost. They can handle 10°F (-12°C) uncovered and -5°F (-21°C) with protection.
• Collard Greens: Similar to kale, collards are extremely cold-hardy and can survive brief periods at 10°F (-12°C) without covers.
• Spinach: A winter staple, spinach can tolerate temperatures down to 15°F (-9°C) without covers and 5°F (-15°C) with a medium-weight row cover.
• Parsnips: These root vegetables become sweeter after a frost and can handle temperatures down to 10°F (-12°C).

Moderately Cold-Tolerant Crops (Need Covers Below 20-25°F / -7 to -4°C)

• Carrots: Mature carrots can survive down to 20°F (-7°C) uncovered. With a row cover, they can handle temperatures as low as 10°F (-12°C).
• Beets: Both the greens and roots can tolerate light frosts. They need covers when temperatures drop below 20°F (-7°C).
• Swiss Chard: This leafy green can handle light frosts but should be covered when temperatures fall below 25°F (-4°C).
• Leeks: Hardy to about 20°F (-7°C), leeks benefit from row covers in colder climates to prevent the ground from freezing.
• Cabbage: Mature heads can tolerate temperatures down to 20°F (-7°C), but young plants need protection at 25°F (-4°C).

Least Cold-Tolerant Crops (Need Covers Below 28°F / -2°C)

• Lettuce: Most varieties can handle light frosts down to 25°F (-4°C) but need covers when temperatures drop below that. Butterhead types are the most cold-sensitive.
• Arugula: This peppery green can tolerate light frosts but should be covered when temperatures fall below 25°F (-4°C).
• Radishes: While they grow well in cool weather, radishes need protection when temperatures drop below 28°F (-2°C).
• Green Onions: These can handle light frosts but require covers when temperatures fall below 25°F (-4°C).
• Cilantro: This herb bolts in heat but can be damaged by hard frosts. Cover when temperatures drop below 28°F (-2°C).

Important: Young seedlings are always more vulnerable than mature plants. Even cold-hardy crops may need extra protection when they’re young.

How to Choose the Right Row Cover for Your Winter Crops

Selecting the right row cover depends on your climate, the crops you’re growing, and the level of protection needed. The wrong choice can lead to overheating, insufficient warmth, or blocked light. Here’s how to pick the best option for what temperature do winter crops need:

Factors to Consider When Choosing a Row Cover

1. Weight and Thickness:
   • Lightweight (0.5 oz/yd²): Adds 2-4°F of warmth. Best for early fall or spring, insect protection, or mild climates.
   • Medium (1.0 oz/yd²): Adds 4-6°F of warmth. The most versatile option for most winter crops in moderate climates.
   • Heavy (1.5-2.0 oz/yd²): Adds 8-12°F of warmth. Essential for extreme cold, hard freezes, or very sensitive crops.
2. Material:
   • Spunbonded Polypropylene: The most common type. Durable, breathable, and allows light and water to pass through.
   • Polyester: More durable than polypropylene but less breathable. Often used for heavyweight covers.
   • Fleece: Provides excellent insulation but may block too much light for long-term use.
3. Light Transmission:
   • Lightweight covers allow 85-90% of light through.
   • Medium covers allow 70-80% of light.
   • Heavy covers allow 30-50% of light, which can stunt growth if left on too long.
4. Breathability: Allows air and moisture to pass through, preventing condensation and mold. Spunbonded fabrics are the most breathable.
5. UV Resistance: Some covers are treated to resist UV degradation, extending their lifespan. Look for this feature if you plan to reuse covers for multiple seasons.

For most gardeners, a medium-weight (1.0 oz/yd²) spunbonded polypropylene cover offers the best balance of protection, light transmission, and breathability for winter crops.

Step-by-Step Guide to Installing Row Covers

Proper installation is key to maximizing the effectiveness of your row covers. A poorly installed cover can blow away, sag under snow, or fail to provide adequate protection. Follow these steps to ensure your winter crops need row covers at the right temperature:

What You Need

• Row cover fabric (appropriate weight for your crops)
• Garden hoops or wire (9-gauge or thicker) for support
• Earth staples, sandbags, or bricks to secure edges
• Scissors or utility knife
• Measuring tape
• Gloves (optional)

Step-by-Step Installation

1. Measure Your Garden Bed: Determine the length and width of the area you need to cover. Add an extra 12-18 inches on all sides to allow for securing the edges.
2. Insert Hoops or Supports: For raised beds or wide rows, insert garden hoops every 3-4 feet. For single rows, you can drape the cover directly over the plants without hoops.
3. Drape the Cover: Lay the row cover fabric over the hoops or plants, ensuring it reaches the ground on all sides. Avoid pulling it too tight, as this can restrict plant growth.
4. Secure the Edges: Bury the edges with soil, weigh them down with sandbags or bricks, or use earth staples to anchor them. This prevents wind from lifting the cover.
5. Check for Sagging: If the cover sags between hoops, add more supports or adjust the tension. Sagging can allow cold air to pool and reduce effectiveness.
6. Vent on Warm Days: On days when temperatures rise above 50°F (10°C), lift or remove the cover to prevent overheating and allow for pollination (if needed).

Warning: Never leave row covers on during warm, sunny days without ventilation. Temperatures under the cover can rise 10-15°F above ambient, which can cook your plants.

Pro Tips for Better Results

• Use Hoops for Tall Plants: If you’re covering tall crops like Brussels sprouts or broccoli, use taller hoops to prevent the fabric from pressing down on the plants.
• Layer for Extreme Cold: In very cold climates, you can layer row covers. Start with a medium-weight cover over hoops, then add a heavier cover on top for extra insulation.
• Monitor Plant Growth: Check under the cover regularly. If plants are growing tall, adjust the hoops or loosen the cover to avoid stunting their growth.
• Remove Snow Buildup: If snow accumulates on the cover, gently brush it off to prevent the fabric from sagging or tearing.
• Rotate Covers: If you’re using covers for both frost protection and insect control, switch to a lighter weight in the spring to allow for better airflow and light transmission.

Common Mistakes to Avoid with Row Covers

Even experienced gardeners can make mistakes when using row covers, which can reduce their effectiveness or even harm plants. Here are the most common pitfalls to avoid when determining what temperature do winter crops need for protection:

1. Using the Wrong Weight: Using a lightweight cover for a hard freeze or a heavy cover for mild frosts can both be problematic. Light covers won’t provide enough warmth, while heavy covers can block too much light and stunt growth.
2. Not Securing the Edges: Wind can easily lift an unsecured cover, exposing your plants to cold and wind damage. Always bury or weigh down the edges.
3. Leaving Covers On Too Long: Row covers are not meant to stay on 24/7. On warm days, remove or vent them to prevent overheating and allow for air circulation.
4. Ignoring Plant Growth: As plants grow taller, the cover can become too tight, restricting growth or causing damage. Adjust hoops or loosen the cover as needed.
5. Using Damaged Fabric: Holes or tears in the cover reduce its effectiveness. Inspect your covers before each use and patch or replace them if necessary.
6. Not Checking the Forecast: Always check the weather forecast before installing or removing covers. A sudden temperature drop can catch you off guard.
7. Blocking Pollinators: Some winter crops, like certain brassicas, may still need pollination. Remove covers during the day to allow bees and other pollinators to access the flowers.

How to Care for and Store Row Covers

Proper care and storage can extend the life of your row covers, saving you money and ensuring they’re ready when you need them. Here’s how to maintain them:

Cleaning Your Row Covers

• Shake Off Debris: After each use, shake off dirt, leaves, and other debris. This prevents mold and mildew from developing during storage.
• Hand Wash with Mild Soap: If your covers are dirty, wash them by hand using mild soap and lukewarm water. Avoid harsh detergents or bleach, as they can damage the fabric.
• Rinse Thoroughly: Rinse the covers well to remove all soap residue. Soap left on the fabric can attract dirt and reduce its effectiveness.
• Air Dry: Hang the covers to dry completely in a well-ventilated area. Avoid using a dryer, as the heat can shrink or melt the fabric.

Storing Your Row Covers

• Ensure They’re Completely Dry: Store only when fully dry to prevent mold and mildew. Even slight dampness can lead to mold growth over time.
• Fold Neatly: Fold the covers neatly to avoid creases or wrinkles that can weaken the fabric. Store them in a cool, dry place away from direct sunlight.
• Avoid Plastic Bags: Storing covers in plastic bags can trap moisture and lead to mold. Use a breathable storage bag or a cardboard box instead.
• Keep Away from Pests: Store covers in a sealed container or elevated off the ground to protect them from rodents and insects.

Important: Most row covers last 3-5 years with proper care. UV-resistant covers may last even longer, but their effectiveness can diminish over time.

What Are the Alternatives to Row Covers?

While row covers are one of the most effective ways to protect winter crops, they’re not the only option. Depending on your climate, crops, and resources, you might consider these alternatives:

Low Tunnels

• Description: Low tunnels are similar to row covers but use a more permanent frame (often PVC pipes or metal hoops) to support the fabric. They’re taller and more spacious than traditional row covers.
• Pros:
  • Provide more headroom for taller plants.
  • Easier to vent and access plants.
  • Can be left in place for longer periods.
• Cons:
  • More expensive and time-consuming to set up.
  • Require more materials and space.
• Best For: Gardeners with larger plots or those growing taller crops like Brussels sprouts or trellised peas.

Cold Frames

• Description: Cold frames are bottomless boxes with transparent or translucent tops (usually glass or plastic) that trap heat from the sun. They’re placed over plants to create a mini greenhouse.
• Pros:
  • Provide excellent heat retention, even in very cold climates.
  • Can be used to start seedlings early or extend the growing season.
• Cons:
  • Less portable than row covers.
  • Require more maintenance (venting on warm days).
• Best For: Small gardens or container plants, and for starting seedlings in early spring.

Mulch

• Description: Mulch is a layer of organic or inorganic material (like straw, leaves, or wood chips) spread around plants to insulate the soil and retain moisture.
• Pros:
  • Easy to apply and remove.
  • Improves soil health as it breaks down.
  • Can be used in combination with row covers for extra protection.
• Cons:
  • Doesn’t protect foliage from frost or wind.
  • Can attract pests if not managed properly.
• Best For: Root crops like carrots, beets, and parsnips, and for insulating the soil around cold-hardy greens.

Plastic Sheeting

• Description: Clear or white plastic sheeting can be used to create a temporary greenhouse effect over plants.
• Pros:
  • Provides excellent heat retention.
  • Can be used to create mini greenhouses or tunnels.
• Cons:
  • Blocks light if not clear, which can stunt plant growth.
  • Doesn’t breathe, which can lead to condensation and mold.
  • Can overheat plants if not vented properly.
• Best For: Short-term use during extreme cold snaps, but not ideal for long-term protection.

For most gardeners, row covers offer the best balance of protection, ease of use, and affordability for winter crops.

Frequently Asked Questions

What is the minimum temperature for row covers?

The minimum temperature for row covers depends on the fabric’s weight. Lightweight covers protect down to 28°F (-2°C), medium covers to 20°F (-7°C), and heavy covers to 10°F (-12°C) or lower. Always check the manufacturer’s rating for your specific cover.

How much warmth do row covers add?

Row covers typically add 2-4°F (1-2°C) for lightweight fabric, 4-6°F (2-3°C) for medium weight, and 8-12°F (4-6°C) for heavyweight covers. The actual warmth depends on factors like wind, humidity, and how well the cover is secured.

Can I leave row covers on all winter?

No, you should not leave row covers on all winter. Remove or vent them on warm days (above 50°F/10°C) to prevent overheating, allow for air circulation, and permit pollination if needed. Prolonged use without ventilation can stunt plant growth or cause disease.

Do row covers block sunlight?

Row covers do block some sunlight, but the amount varies by weight. Lightweight covers block about 10-15% of light, medium covers 20-30%, and heavy covers 50-70%. For most winter crops, medium-weight covers provide a good balance of protection and light transmission.

How do I know if my plants need row covers?

Your plants need row covers when the forecast predicts temperatures at or below the minimum tolerance for your specific crops. For example, cover lettuce when temps drop below 28°F (-2°C) and kale when they fall below 20°F (-7°C). Also, use covers to protect against wind, frost, or pests.

Final Thoughts

Understanding what temperature do winter crops need for row covers is essential for protecting your garden from cold snaps and extending your growing season. Most winter crops benefit from covers when temperatures drop below 28°F (-2°C), but the exact threshold depends on the plant’s hardiness and the cover’s weight. Medium-weight row covers offer the best balance of protection and light transmission for most winter vegetables.

Remember to secure covers properly, vent them on warm days, and monitor your plants for signs of stress or overheating. With the right approach, row covers can help you enjoy fresh, homegrown produce all winter long.