Frost Protection for $20: Covers That Buy You Weeks

The first frost does not end my garden. It ends the part of my garden I failed to cover. Zone 6 gardens like mine in East Tennessee usually see a first frost between October 15 and November 1, and Zone 7 between November 1 and November 15, according to Garden Growth Guru's zone-by-zone ranges. That is days to weeks away, which means this is the weekend to buy or build protection, while the crops it saves are still alive to save.

What each cheap cover actually buys you, in degrees

I trust extension numbers over product packaging, so here is the honest ladder. A floating row cover, the lightweight fabric draped directly on the crop, generally provides about 4 to 5 degrees of frost protection, according to Virginia Tech guidance summarized by Penn Hort, which notes that this lets cool-season crops survive air temperatures as low as 28 degrees Fahrenheit. The University of Georgia Extension is more generous for a well-set low tunnel or hoop cover: row covers can provide as much as an 8-degree temperature difference, and UGA puts the cost as low as $20 to cover a row 4 feet wide by 50 feet long with reusable material. A cold frame, a bottomless box with a transparent lid, runs 10 to 15 degrees warmer than the outside air and extends harvest by 4 to 8 weeks, per Garden Growth Guru's season-extension guide.

Figure 1: Temperature protection by cover type. Sources: University of Georgia Extension; Virginia Tech via Penn Hort; Garden Growth Guru.

Degrees only matter against what your crops can already take. Kale and collards survive to about 20 degrees, and spinach and mache to about 15 degrees, according to Gardenly's October checklist. Do that subtraction and the case makes itself: a 28-degree night, which is a killing night for tender greens, is a non-event for covered kale. The crops that need you most are the tender ones still producing: peppers and tomatoes are damaged at or near freezing, and basil suffers irreversible injury well above it. I harvest basil outright before the first cold night and stop pretending a blanket will save it.

How I deploy covers so they work

Water first. I water dry soil earlier in the day, because moist soil stores more daytime heat to release overnight. Then I lay the cover before temperatures fall and secure every edge with rocks, soil, or staples, because a loose cover in wind is just laundry. Two failure modes from experience and from UGA's guidance: leaves touching a floating cover can freeze right through the contact point, so taller or tender crops get hoops; and covers come off or get vented when the air under them climbs toward 80 degrees on a sunny day, per the Virginia Tech guidance, or you cook what you saved. One more rule I follow: on a clear, calm night, the surface of my beds can run several degrees colder than the forecast air temperature, so I cover when the forecast says 36, not when it says 32.

The $20 setup I recommend for one bed

For a single 4-by-50-foot row, UGA's figure is the whole pitch: about $20 of reusable polyspun cover, laid over hoops or floated, used two seasons if you store it dry. My order of operations this week: cover the kale, spinach, and carrots first because they repay it longest; mulch root crops heavily so I can keep digging them after the tops die back; build or set one cold frame over the salad greens I most want in December. Twenty dollars and one afternoon, against weeks of greens I would otherwise buy. That is the best exchange rate left in my garden this year.

FAQ

How much frost protection does a row cover give? About 4 to 5 degrees for a typical floating cover (Virginia Tech via Penn Hort), and as much as 8 degrees for a hoop-supported low tunnel, according to the University of Georgia Extension.

How much does it cost to cover a garden row? As little as $20 for a 4-foot by 50-foot row with reusable row cover material, per the University of Georgia Extension, and the material lasts about two seasons if stored dry.

Which vegetables survive frost without much help? Kale and collards survive to about 20 degrees Fahrenheit and spinach and mache to about 15 degrees, according to Gardenly's October garden checklist. Light frost actually sweetens many brassicas and roots.

When should I put covers on? Water earlier in the day, cover before temperatures fall, and secure the edges. Vent or remove covers when the air beneath reaches about 80 degrees on sunny days.