Frost Cloth for Plants: How to Choose and Use It

Frost cloth is a light, breathable fabric (also sold as a frost blanket or floating row cover) that you lay over plants on cold nights. It traps heat rising from the soil, so the air under it stays a few degrees warmer than the open garden. For most home gardens, a medium-weight frost cloth of about 0.5 to 1.0 ounce per square yard, draped to the ground and pinned at the edges, is the right pick, because it handles typical light frosts while still letting in enough light to leave on for a day or two.

Those few degrees decide a lot. Tomatoes and peppers can be hurt at 33°F, and a cover that holds the air near 30°F instead of 27°F can be the difference between a full harvest and blackened leaves.

We grow a home garden in USDA Zone 7b, where swings around freezing show up in both spring and fall. Once you know which fabric to buy and how to put it down, you can save tender plants on cold nights and stretch your harvest by weeks.

Key Takeaways

• Frost cloth works by holding soil heat close to plants, and it only buys a few degrees.
• Heavier fabric protects more but blocks more light, so match the weight to the job.
• Cover in the afternoon before a freeze, pin the edges to the ground, and vent on sunny days.

How Does Frost Cloth Protect Plants?

Frost cloth protects plants by trapping heat that the ground releases at night, keeping the air around leaves a little warmer than the air outside. That warmth comes from the soil itself, which is why how you lay the fabric counts as much as which fabric you buy, and why even a good cover has a ceiling in a hard freeze.

How Breathable Covers Retain Soil Warmth

Soil soaks up heat during the day. On clear, calm nights, it gives that heat back to the sky fast. A frost blanket slows the escape, holding a pocket of warmer air over your plants.

Most row cover is spunbonded polypropylene or polyester. It looks like thin white felt. Because it’s porous, air, rain, and light pass through it, and you can leave it on through a cloudy day without cooking your plants.

That breathability is the big difference from plastic. Plastic holds heat well, but it traps too much on sunny days, and leaves that touch cold plastic can freeze. Fabric is far more forgiving for beginners.

A few things help the cover hold more heat:

• Edges on the ground. Heat leaks out of any gap. A cover that stops halfway down the plant protects little.
• An air gap. Fabric resting on hoops gives an insulating layer of air between the cloth and the leaves.
• Moist soil. Wet soil stores more heat than dry soil and releases it through the night.

Why Frost Protection Has Limits in a Hard Freeze

A cover raises the temperature underneath by only a few degrees. Extension research puts most fabric covers at roughly 2°F to 10°F warmer than the open air, depending on weight. A lightweight sheet of about 0.6 ounce adds only 2 to 3 degrees.

That’s enough for a light frost. It isn’t enough when the forecast calls for the low 20s or teens for hours. The cover has no heat source of its own, so on a long, windy, bitter night it eventually drops toward the outside temperature.

Places where fabric presses directly on tender parts, like open blossoms, can still get frost damage even under a cover. In a hard freeze, harvest what you can, move pots into a garage or shed, and think of the cover as a backup, with a heavier fabric or a double layer for anything you can’t move.

Which Fabric Weight and Cover Size Do You Need?

Pick fabric weight by how cold your nights get, and pick size by how much ground you need to reach. Weight is listed in ounces per square yard, and heavier fabric gives more warmth but lets through less light.

Compare Fabric Weights, Claimed Protection, and Light Transmission

The numbers below come from extension guidance and common manufacturer claims. Treat them as rough ranges, since wind, cloud cover, and how well you seal the edges all change real results.

Fabric class	Weight (oz/sq yd)	Light let through	Typical claimed protection
Lightweight (insect barrier)	about 0.45	about 90%	little frost protection
Medium weight	about 0.5 to 0.55	about 85%	down to about 28°F
Heavyweight	about 0.9 to 2.0	about 30% to 50%	about 24°F to 28°F

Some of the heaviest fabrics are sold as protecting plants near 20°F. Read those claims as best case, with edges sealed tight and no wind.

Choose Lightweight or Heavyweight Covers for Your Plants

Choose by how long the cover stays on and how cold it gets.

• Lightweight (under 0.5 oz): Best for keeping bugs off cabbage, kale, and greens in late spring. It lets in plenty of light for long stretches but adds almost no warmth.
• Medium (0.5 to 1.0 oz): The all-around choice for frost nights in spring and fall. Plants can sit under it for a day or two without starving for light.
• Heavy (1.0 to 2.0 oz): For colder nights and tender plants. It blocks half or more of the light, so pull it off or open it during the day.

If you can buy only one, a medium weight around 0.9 to 1.0 oz covers the most situations. For a surprise colder night, you can lay two layers.

Measure for Ground Coverage and Check Reusability

Measure the bed width, then add the plant height twice so the fabric can drape over the top and reach the soil on both sides. Add another foot or so per side for pinning.

As a rule, a 6-foot-wide piece covers a 3-foot-wide bed with room for upright seedlings. Rolls come about 6 to 10 feet wide or more, and from about 20 feet to hundreds of feet long. For shrubs and small trees, look for drawstring or zippered “plant jacket” bags.

Lightweight fabric tears easily and may last only a few months. Medium and heavy covers last several seasons with care: rinse off mud, dry them fully, and store them indoors in a sealed bin, since mice like to nest in fabric left in sheds.

When and How Should You Cover Plants Before a Freeze?

Cover plants in the afternoon before a forecast low near or below 32°F, with the fabric reaching the ground and pinned tight. Good timing comes from pairing the forecast with how much cold each plant can take, then prepping the soil and the cover before sundown.

Use Forecast Lows and Plant Tolerance to Decide When to Cover

Start with the plants. Warm-season crops like tomatoes, peppers, cucumbers, squash, melons, and basil can be damaged at 33°F, so cover them any time the forecast low hits the mid-30s.

Cool-season crops like peas, lettuce, spinach, beets, carrots, onions, broccoli, cabbage, and cauliflower handle light frosts with little harm. Cover them when lows drop into the upper 20s or below, or when they’re freshly planted.

Watch for clear, calm nights. Frost can form even when the air reads a few degrees above freezing, because leaves and low spots lose heat faster than a thermometer at eye level. Garden spots at the bottom of a slope run colder than beds near a south- or west-facing wall.

Water Dry Soil Ahead of Freezing Weather

Water dry beds during the day before a freeze. Moist soil holds more heat than dry soil, so it has more warmth to give back under the cover overnight.

Water in the morning or early afternoon so leaves have time to dry before dark. Soak the root zone, not the foliage. Skip it if the ground is already damp from rain, since soggy soil adds nothing.

Drape to the Ground, Add Hoops Where Needed, and Secure the Edges

1. Put covers on in the afternoon. This traps the day’s warmth before the soil starts losing it.
2. Decide on hoops or no hoops. Light fabric can rest right on sturdy plants. For tall, bushy, or flowering plants, set wire, metal, or bendable PVC hoops so the cloth sits above the leaves.
3. Drape all the way to the soil. The fabric should touch the ground on every side.
4. Leave some slack. Loose fabric lets plants push up without strain.
5. Pin the edges. Use landscape staples, bricks, boards, sandbags, or a line of soil every few feet. In windy spots, tie the ends to stakes.

Flapping fabric rubs and damages leaves, and wind can lift a loose cover away entirely, so a tight seal pays off twice.

Vent or Remove Covers When Sunny Days Warm Up

Pull covers back once morning temperatures climb above freezing, especially on sunny days. Even breathable fabric builds heat, and heavier weights cut light a lot.

Extension advice is to open or remove covers when it regularly runs above 90°F underneath. On cloudy, cold days, medium fabric can stay on. For squash, cucumbers, and melons, remove covers once they bloom so bees can reach the flowers.

How Can Covers Extend Your Spring and Fall Growing Seasons?

Row cover lets you plant a bit earlier in spring and keep harvesting later in fall, because it softens the cold nights at both ends of the season. Timing it to your local frost dates makes the difference.

Protect Spring Plantings Around Your Local Last Frost Date

Your last frost date is an average, and many date tables use a 30% chance of frost after the listed day. Late frosts happen, which is why it pays to keep covers handy for a few weeks past that date.

Hardy crops like peas, spinach, radishes, carrots, onions, and lettuce can go in before the last frost. A medium cover over them shields young seedlings from wind and the odd hard night, and also keeps birds off pea and bean sprouts.

Tender transplants like tomatoes and peppers should wait until frost danger passes. If you plant close to the date, lay a frost cloth over hoops on cold nights. If you’re new to timing beds, our tips on starting your own garden as a beginner cover the planting basics.

Keep Cool-Season Crops Growing Through Fall Frosts

Fall is where covers shine for many gardeners. Kale, cabbage, broccoli, spinach, lettuce, and other leafy greens keep growing in cool weather, and a cover helps them ride through the first frosty nights.

In Zone 7b, first fall frosts commonly arrive around late October to early November, and plenty of mild days follow. A medium or heavy cover on the cold nights can keep greens coming for weeks. A heavier “garden quilt” fabric can also coax a few more weeks from tomato and pepper plants before frost ends them.

Use the Planting-Zone and Frost-Date Lookup by ZIP Code

Your USDA hardiness zone tells you the average coldest winter temperature where you live, in 10-degree zones and 5-degree half zones. It helps with perennials and with how hard your winters bite.

Frost dates tell you when your season starts and ends. Our planting zone and frost date lookup by ZIP code gives you both in one place, so you can see your last spring and first fall frost averages before you plant and have covers ready for the weeks on either side of those dates.

Match Your Cover to the Forecast and Your Plants

Pick your cover by the forecast low and the plant’s cold tolerance, then put it down so the soil’s heat stays inside. A medium-weight frost cloth handles most light frosts, a heavy fabric or double layer helps on colder nights, and nothing fabric-based will reliably save tender plants through long hours in the low 20s.

A quick guide:

• Low in the mid-30s: Cover warm-season crops with medium fabric.
• Low around 28°F to 32°F: Medium fabric on hoops for tender plants; hardy greens usually manage fine.
• Low in the mid-20s: Heavy fabric or two layers; move pots indoors.
• Low near 20°F or below: Harvest tender crops and protect only the toughest plants.

Water dry soil earlier in the day, cover in the afternoon, pin every edge, and open the cover once the morning sun warms things up.

Frequently Asked Questions