Row cover is the cheaper and far more flexible option: it covers whatever shape you need, costs a fraction of a frame, and heavy grades buy roughly six to eight degrees Fahrenheit of frost protection. A cold frame protects better on a hard night, holds up in wind and lasts years. In practice the best answer is often both, with fabric laid over plants inside the frame, which stacks the protection.
Heavy row cover
Roughly 6 to 8 F of protection
Light row cover
About 0.55 oz, more light through
Cold frame
A few degrees, plus wind shelter
Stacking both
The cheapest extra protection there is
Researched from published specifications and verified owner reviews · Updated 2026-08-16
Both work by the same physics: they slow the loss of heat radiating away from the ground and the plants on a clear still night. Neither generates heat. That is why both perform best on a still frosty night and least well in wind, and why the gain is measured in a handful of degrees rather than a transformation.
The comparison
Figure 1. Row cover fabric against a cold frame·8 rows
Figure 1. Row cover fabric against a cold frame
Measure
Row cover
Cold frame
Cost per covered area
Very low
High
Frost protection
6 to 8 F for heavy grades
A few degrees, more if twin-walled
Can stay on in daylight
Yes for light grades
No, must be vented
Wind resistance
Poor unless pinned
Good
Covers awkward shapes
Yes
No, fixed footprint
Lifespan
A few seasons
Years
Insect exclusion
Yes, as a side effect
Partial
Light transmission
Reduced, grade dependent
High
Frost protection figures are manufacturer guidance for still conditions. Researched general information rather than professional advice.
Weight is the specification that matters
Row cover is sold by fabric weight, and the two ends of the range do different jobs. A light Agfabric Frost Blanket, 0.55 oz, 10 x 100 ft ($32.61) at 0.55 ounces transmits far more light, so it can be left on through the day for a run of mild frosty nights without checking the crop yellows underneath.
A heavy AlpineReach Frost and Sun Plant Cover, 10 x 50 ft ($36.99) at 1.2 ounces buys considerably more protection, in the region of six to eight degrees Fahrenheit, and blocks correspondingly more light. That is the grade for a hard night, laid on in the evening and pulled back in the morning.
Hoops keep fabric off the leaves
Fabric resting directly on foliage conducts heat away at the contact points and produces frost damage in exactly the pattern of the cover. Hoops solve it, and a HEKIWAY Frost Cloth Kit with 7 Garden Hoops ($59.99) supplies both parts in one box. Pin the edges down with Sandbaggy 6 in Landscape Staples, 200 Count ($54.97) because an unpinned cover in wind is worse than none, flapping and abrading the crop before it leaves entirely.
Note
The same fabric excludes insects, and the same fabric excludes pollinators
Fine mesh and light row cover over a crop keeps cabbage white, leaf miner and carrot fly off it. That is a benefit for leaf and root crops and a problem for anything that needs pollinating, so covers come off fruiting crops when flowering starts, or the flowers get hand pollinated instead.
Where the frame wins
Wind, and duration. A Outsunny Wooden Cold Frame, 39 x 26 in ($63.53) does not need pinning, does not flap and does not need putting on and taking off. For overwintering pots and hardening off over several weeks, that convenience is the whole argument, and it is a good one. A frame also holds a crop through weather that would have shredded fabric.
The decision, summarised
Protecting a bed or a long row: fabric on hoops, pinned down.
Hardening off and overwintering pots: a cold frame.
A hard frost forecast tonight: heavy fabric, on before dusk, off in the morning.
A run of mild frosty nights: light fabric, left on through the day.
The coldest nights of the year: both, with fabric over the plants inside the frame.
Fabric weights and the frame
The two grades of cover, the hoops that keep them off the crop, and the structure that needs neither.
+- How many degrees of frost protection does row cover give?
Manufacturers commonly quote around two to four degrees Fahrenheit for light grades and six to eight for heavy ones, measured in still conditions. Wind reduces it substantially, because the mechanism is trapping radiated heat rather than insulating against moving air. Doubling the fabric adds protection but also halves the light, so it is a night-time measure rather than a permanent one.
+- Can row cover stay on all the time?
Light grades can, for weeks, and are often used that way over brassicas both for frost and for insect exclusion. Heavy grades cut too much light to leave on for long. Whatever the grade, take covers off flowering crops that need pollinating, and check underneath regularly, because covers hide slug damage and aphid build-up beautifully.
+- Why did my plants get frosted through the cover?
Usually because the fabric was touching the foliage, so heat conducted straight out at the contact points, or because it was windy and the trapped warm air was stripped away. Hoops fix the first and pinning the edges down fixes the second. A hard enough frost will get through any unheated cover regardless, and that is the limit of the method rather than a fault in it.
+- Does row cover work inside a greenhouse?
Yes, and it is one of the cheapest ways to hold a crop through a cold snap without heating the whole volume. An inner layer laid over the crop at night creates a second small envelope inside the house, which is a well established technique for unheated winter growing. Pull it back during the day so the crop gets full light.
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