Row cover is a lightweight, permeable fabric providing frost protection, wind buffering, and pest exclusion. A 25-foot roll costs $10-25 and lasts 2-5 seasons. The key is choosing the right weight for your zone and knowing when to use it.
The Three Weights of Row Cover
N-30 (0.5 oz/sq yd): 85-90% light transmission, 2-4°F frost protection. Primary uses: pest exclusion for brassicas and lettuce, wind protection for seedlings, light frost events in zones 6-10.
N-50 (1.0-1.5 oz/sq yd): 70-75% light transmission, 4-6°F frost protection. Most versatile weight for four-season gardening in zones 4-7 — early spring planting and fall harvest extension.
N-70 (2.0-2.5 oz/sq yd): 50-60% light transmission, 6-10°F frost protection. Best for hard freezes and overwintering in zones 3-6. Remove or vent during extended mild spells to prevent etiolation.
When to Use Row Cover by Zone
Zones 3-4: N-70 for spring and fall frost protection; layer N-30 under N-70 for protection into the low teens°F; N-30 for summer pest exclusion. Zones 5-6: N-50 is the primary weight — 3-4 week spring extension and fall harvests through November; N-70 for hard freezes below 28°F; N-30 for summer brassica pest exclusion. Zones 7-8: N-30 handles most frost events; N-50 for the coldest nights; N-70 rarely needed. Zones 9-10: N-30 for light frost and pest exclusion. Zones 11-13: Row cover used primarily for pest exclusion and shade.
How to Apply Row Cover
Row cover must be loose enough to allow plants to expand. Lay it over low tunnels (wire hoops or PVC over rebar stakes) for a tent with 6-12 inches of clearance above the canopy. Direct draping works for short-term frost events but restricts growth in extended use. Secure all edges with soil, rocks, or pins — wind lifts edges and reduces protection significantly. For pest exclusion, seal edges at soil level from day one.
Crops That Benefit Most
Brassicas: N-30 all season for pest exclusion eliminates cabbage worm and flea beetle damage without spraying. Lettuce and spinach: N-50 extends spring and fall harvest by 3-4 weeks at each end. Tomato and pepper transplants: N-30 or N-50 for the first 2-3 weeks after transplanting; remove once daytime temps are consistently above 55°F. Root vegetables: N-50 over carrots and parsnips in fall extends harvest well past first frost — these crops sweeten with cold and hold in the ground under cover.
Frequently Asked Questions
- Can I leave row cover on all season?
- N-30 can stay on brassicas all season. N-50 and N-70 should be removed during warm, sunny weather. Always remove from flowering crops — they need pollinator access.
- What is the difference between row cover and hardware store frost cloth?
- Hardware store frost cloth rarely specifies protection ratings. Use rated horticultural fabric (Reemay, Agribon, or N-rated) from a garden supplier for reliable frost protection.
- How do I support row cover?
- Low tunnels from 9-gauge wire hoops placed every 3-4 feet support row cover 8-12 inches above the crop. Cut wire into 6-foot lengths and push each end 4-6 inches into the soil.
- Can row cover protect against a hard freeze below 20°F?
- N-70 alone protects to about 24°F. Below that, use double layers or a cold frame. Below 20°F, only kale, spinach, and mâche have a reasonable chance.