Row Cover

Row cover is spunbonded polypropylene fabric draped directly over plants or laid over hoops to modify the microclimate around growing crops. It transmits light and allows gas exchange while reducing temperature fluctuations and blocking pest access. It’s the most versatile and cost-effective season extension and pest exclusion tool in the home garden.

How It Works

The fabric traps radiated heat at the soil surface during the night, reducing the rate of temperature drop around protected plants. In wind, it acts as a buffer, reducing wind chill. During the day, it transmits 80-95% of available light depending on weight, allowing normal photosynthesis.

Row cover works by holding a modified microclimate - it doesn’t heat itself or the soil, it reduces the rate of heat loss. On a still, clear night when radiative cooling is most severe, row cover can protect plants that would otherwise be damaged.

Weights and Their Uses

Lightweight (0.5-0.9 oz/sq yd): Transmits 90%+ of light; provides 2-4°F of frost protection. Used for extending the growing season in spring and fall with minimal impact on plant growth. Can be left on vegetables for weeks at a time. Best for: fall lettuce and spinach extension, early spring frost protection for transplants.

Medium (1.0-1.5 oz/sq yd): Transmits 80-85% of light; provides 4-6°F of frost protection. Used for tomato and pepper transplant protection in early spring. Some light reduction becomes noticeable on overcast days.

Heavy frost blanket (1.5-3.0 oz/sq yd): Transmits 50-70% of light; provides 6-10°F of frost protection. Too heavy for extended use during the growing season because light reduction affects growth, but valuable for one-night or short-duration cold events. Used to protect tender plants against unexpected late frosts.

Row cover is sold in rolls by width (typically 5, 7, or 12 feet) and length (25-500 feet). A 100-foot roll of 7-foot-wide lightweight cover costs $20-35 and covers roughly 700 square feet. It’s reusable for 2-5 seasons if handled carefully.

Pest Exclusion

Laid over crops before pest populations establish and held in place with soil, pins, or weights at the edges, row cover physically excludes:

• Cabbage moths and butterflies (Pieris rapae, Pieris brassicae) - preventing cabbage looper and imported cabbageworm
• Cucumber beetles (which spread bacterial wilt)
• Squash vine borer moths
• Carrot rust fly (Psila rosae)
• Flea beetles

For pest exclusion, the cover must be installed at planting or transplanting and sealed at edges before the pest population establishes. Gaps allow entry. Remove when crops require pollination, or use a permeable cover that allows bee access (not all pest-exclusion applications are compatible with pollinator access).

Ventilation

Closed row covers accumulate heat during sunny days. Lightweight covers over frost-hardy crops in fall or spring can be left closed indefinitely. Over heat-sensitive crops in summer, the temperature buildup under cover can stress plants. Open the ends or remove covers on warm days when frost risk is not present.

Application Methods

Direct drape: Lay fabric directly on plants. Plants push fabric up as they grow, which keeps the fabric in contact with the canopy rather than elevated above it. Works for low-growing crops; not suitable for tall crops where fabric contact increases disease pressure.

On hoops: Bent rebar, wire, or flexible plastic pipe creates a tunnel that holds the cover above the canopy. Better air circulation reduces disease pressure. Allows the cover to be raised or removed without disturbing plants.

Weighted edges: Sandbags, rocks, soil, or fabric anchoring pins hold edges down. Gaps defeat both frost protection and pest exclusion purposes.