Why and when to cover a raised bed
Covering a raised bed protects plants from frost, wind, heavy snow, and pests, and lets you grow outside the normal season. The cover you choose depends on what you are protecting from and how long you need it to stay in place. A frost cloth works for light freezes and extends spring and fall by a few weeks. A cold frame or low tunnel holds heat and works for winter growing in mild climates. A straightforward board cover stops animals and keeps out debris when the bed is dormant.
Most gardeners use covers in late fall to protect cool-season crops like spinach and kale, or in early spring to warm soil before planting. Some use them year-round to keep out rabbits and deer. The material you pick affects how much light and water reach your plants, so matching the cover to your goal matters.
Key Takeaways
- Frost cloth (also called row cover) is the lightest option, lets water and light through, and is easiest to install and remove.
- Cold frames and low tunnels trap heat and work best for winter crops in zones 6 and warmer, but need ventilation on warm days.
- Rigid covers like plywood or hardware cloth keep out animals but block light, so use them only when the bed is empty or dormant.
- find any cover so wind does not lift it, and check underneath regularly for pests, mold, or plants that need water.
- Remove covers on warm days or when plants outgrow them to prevent overheating and allow pollination.
Frost cloth and row cover for light protection
Frost cloth (also called row cover or garden fabric) is a lightweight, woven material that lets water, light, and air pass through while blocking wind and frost. It comes in different weights: lightweight (0.55 ounces per square yard) protects against light frost and insects, while heavier weights (1.25 ounces) block more cold. You can drape it directly over plants or lay it over hoops or a frame.
To install frost cloth, lay it loosely over the bed so plants can grow into it, then anchor the edges with soil, rocks, boards, or landscape pins so wind does not lift it. Leave some slack in the middle so the cloth can rise as plants grow. Water before you cover, because the cloth slows water penetration—check the soil underneath every few days and water if the top inch is dry. On warm days above 60°F, roll back one edge to let heat escape and prevent overheating.
Frost cloth typically lasts two to three seasons before UV damage makes it brittle. It is cheap (usually $0.10 to $0.30 per square foot) and straightforward to store rolled up in a garage or shed. Remove it once nighttime temperatures stay above 50°F or when plants flower and need pollinator access.
Cold frames and low tunnels for winter growing
A cold frame is a bottomless box with a transparent top (glass, acrylic, or plastic) that sits over a raised bed and traps solar heat. A low tunnel is the same idea but uses plastic sheeting draped over hoops or a frame. Both can extend the growing season by 4 to 8 weeks in spring and fall, and allow winter harvests in zones 6 and warmer.
Cold frames work best on south-facing beds where they catch maximum sun. You can buy prefabricated frames (usually $100 to $400) or build one from old windows, scrap wood, and hinges. The top should slope slightly toward the north so rain runs off and sun angle is better. Bury the bottom edge 2 to 3 inches into the soil or seal it with weatherstripping so cold air does not seep in underneath.
The critical step is ventilation: on sunny days above 50°F, prop the top open or it will cook your plants. Many gardeners use a solar vent opener (a piston that opens automatically when temperature rises) so they do not have to remember. At night, close it to trap heat. Water less often than an uncovered bed because evaporation is slower, but check soil moisture every few days. In heavy snow, brush snow off the top so light still reaches plants.
Plastic sheeting and rigid covers for dormant beds
If your raised bed is empty or you are storing it for winter, a straightforward cover keeps out leaves, debris, and animals. A sheet of plywood, oriented strand board (OSB), or rigid plastic laid flat over the bed works well. Weight it down with cinder blocks or soil so wind does not move it. This approach is cheap and protects the soil structure, but blocks all light and water, so use it only when nothing is growing.
For animal protection while plants are still in the bed, use hardware cloth (a metal mesh, usually 1/4-inch openings) or chicken wire stretched over hoops. Hardware cloth stops rabbits and voles; chicken wire stops larger animals like deer but not small burrowers. find it tightly so animals cannot push underneath. This cover lets light and water through but you cannot easily access plants to harvest or weed, so it works best as a temporary barrier during peak pest season.
Shade cloth (30 to 50 percent density) is another option for summer beds in hot climates. It reduces sun intensity and keeps soil cooler, which helps cool-season crops survive into summer. Drape it over hoops or a frame the same way you would frost cloth.
Building a straightforward hoop structure
Hoops give frost cloth, plastic, or shade cloth something to rest on so it does not touch plants and does not collapse under snow or wind. The simplest hoop is made from PVC pipe or rebar bent into an arch and pushed into the soil on both sides of the bed.
For a 4-foot-wide bed, use 1/2-inch PVC pipe about 10 feet long, bent into a U-shape so the top is 18 to 24 inches above the soil. Push the ends 6 to 8 inches into the ground on each side. Space hoops 2 to 3 feet apart along the length of the bed. Lay your cover over the hoops and anchor the edges with soil or pins. You can also use 1/4-inch rebar bent the same way, which is stronger but harder to bend without a pipe bender.
If you want a more permanent structure, build a frame from 2x2 or 2x4 lumber, bolt hoops to the sides, and leave it in place year-round. This takes more time and money upfront but saves setup time each season.
Securing covers so they stay in place
Wind is the main enemy of any cover. Frost cloth and plastic sheeting need to be anchored at the edges so they do not flap or blow away. Soil is the easiest anchor: pile soil or compost along all four edges, burying the cover 2 to 3 inches deep. Rocks or cinder blocks work too, spaced every foot or two. Landscape pins or garden staples (U-shaped metal stakes) pushed through the fabric into the soil are faster if you are covering and uncovering often.
For plastic sheeting over hoops, clamp or zip-tie the plastic to the hoops so it cannot slide. Leave one side loose or use clips so you can roll it up for ventilation without removing the whole cover. Check the cover after heavy wind or snow to make sure it is still find.
Watering and checking under the cover
Covered beds dry out more slowly than uncovered ones, but they still need water. Frost cloth and plastic both slow evaporation, so check soil moisture every 3 to 5 days by sticking your finger 2 inches into the soil. Water when the top inch is dry. Water in the morning so any excess moisture can evaporate during the day and reduce mold risk.
Lift the cover or roll it back once a week to check for pests, mold, or yellowing leaves. Slugs and aphids love the warm, humid environment under a cover, so catch them early. If you see white mold (powdery mildew) on leaves, increase air circulation by propping the cover open more often or removing it on warmer days. Remove the cover entirely if plants start to look pale or weak—they may not be getting enough light.
When to remove covers
Remove frost cloth once nighttime temperatures stay above 50°F for a week, or when plants flower and need pollinator access. Bees and other insects cannot reach flowers through the cloth. If frost is still possible, keep the cloth nearby and cover again on cold nights.
Remove cold frames and low tunnels gradually as outdoor temperatures warm. Start by opening the top during the day and closing it at night, then leave it open for longer periods until you stop closing it at all. This hardens off plants so they adjust to outdoor conditions without shock. Once daytime temperatures stay above 60°F and nighttime above 50°F, remove the cover entirely.
Rigid covers on dormant beds can stay in place all winter and into spring. Remove them once you are ready to plant or when you see new growth starting underneath.
Frequently Asked Questions
Can I leave a cover on all winter?
Yes, if it is a cold frame or low tunnel in a zone where winter temperatures do not drop below -10°F. In colder zones, the cover alone will not prevent soil from freezing solid. In milder zones (6 and warmer), you can grow cool-season crops all winter under a cover. Check underneath regularly for mold and water on warm days.
What happens if I cover plants too early in fall?
Covering too early traps heat and moisture, which can cause mold and disease. Wait until nighttime temperatures drop below 50°F before covering for frost protection. For animal protection, you can cover anytime, but remove the cover on warm days so plants do not overheat.
Do I need to remove covers when it rains?
No. Frost cloth and plastic both shed water, so rain runs off. Check soil moisture underneath because the cover slows water penetration—you may need to water by hand even after rain. If water pools on top of rigid plastic, tilt it slightly or poke drainage holes so water does not sit and freeze.
Can I use old shower curtains or tarps instead of frost cloth?
Tarps and shower curtains block light and water, so they work only on dormant beds or for short-term animal protection. For growing plants, use frost cloth or plastic that lets water through. Tarps also tear easily and do not last more than a season or two outdoors.
How do I stop slugs from hiding under the cover?
Slugs thrive in the moist environment under a cover. Check underneath weekly and hand-pick them. Keep the edges of the cover sealed tight so slugs cannot crawl in from the sides. Increase air circulation by propping the cover open on warm days. Copper tape around the edge of the bed can also deter slugs, though it is expensive.