Figure 1. The sun warms the soil in the daytime. Heat from the soil keeps crops warm at night. A covering traps heat from the soil around the crops.

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Noreen Chambers
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CMG GardenNtes #722 Frst Prtectin and Extending the Grwing Seasn Outline: Types f frst, page 1 Heat surce at night, page 1 Cverings, page 2 Blankets and sheets, page 2 Flating rw cvers, page 2

when a cld frnt mves int the area. Temperatures may drp significantly belw critical levels thereby making crp prtectin questinable.

Radiatin frsts at the beginning and end f the grwing seasn are typically nly a few degrees belw critical levels, making crp prtectin wrthwhile.

1 CMG GardenNtes #722 Frst Prtectin and Extending the Grwing Seasn Outline: Types f frst, page 1 Heat surce at night, page 1 Cverings, page 2 Blankets and sheets, page 2 Flating rw cvers, page 2 Plastic cvering n frame, page 2 Cld frame made with cncrete reinfrcing mesh, page 3 Adding space blankets, page 4 Lights fr added heat, page 5 Wall f Water, page 6 Types f Frst Advective frsts ccur when a cld frnt mves int the area. Temperatures may drp significantly belw critical levels thereby making crp prtectin questinable. Radiatin frsts ccur n calm clear nights that lack clud cver t hld in heat. Radiatin frsts at the beginning and end f the grwing seasn are typically nly a few degrees belw critical levels, making crp prtectin wrthwhile. Heat Surce at Night Sil, warmed by the sun in the daytime, is the surce f heat fr frst prtectin at night. Mist, smth sil absrbs mre heat. T trap heat frm the sil arund yung vegetables at night, place a cvering that is lw t the grund and spreading. T recharge the heat surce fr the next night, any cvering must allw sunlight t shine thrugh t the sil r must be remved in the daytime. [Figure 1] Figure 1. The sun warms the sil in the daytime. Heat frm the sil keeps crps warm at night. A cvering traps heat frm the sil arund the crps

2 Cverings Blankets and Sheets Grandma s ld methd f cvering the garden with blankets and sheets wrks well as lng as the fabric remains dry. If the fabric absrbs water, evaprative cling can lead t clder temperatures adjacent t the blanket. T recharge the heat stred in the sil, the blankets and sheets must be remved in the daytime. Flating Rw Cvers Flating rw cvers are lightweight fabrics that lay directly ver crps. Because they transmit light, they prvide crp prtectin ver an extended perid f time withut being remved. They prvide 2 F t 4 F f frst prtectin, cut wind n tender plants, and screen ut sme insects. On insect pllinated crps, cvers must be remved fr pllinatin t ccur. [Figure 2] Flating rw cvers are ppular in cmmercial vegetable prductin where crps planted in large blcks are easily cvered with rw cvers. Many brands and fabric types are cmmercially available. Figure 2. Flating rw cver n brccli and cabbage, prtecting crps frm cabbagewrms mths. Clear Plastic Cvering n Frame When plastic is used as a cvering ver a grwing bed, it must be held up ff the plants. Plants will freeze where the plastic tuches them. Tunnel Gardening Gardening catalgs carry wire hps fr use in tunnel r clche gardening. Hps are placed at three t five ft intervals depending n the wind expsure f the site. The wire hps hld up a strip f plastic frming a tunnel-shape cvering dwn the grwing bed. Bury the edges f the plastic a few inches int the sil n all sides. On a raised-bed bx made with lumber, staple the plastic t the sides f the bx. Tw-inch hles cut in the sides f the plastic tunnel at tw t three ft intervals are essential t reduce verheating. This type f cvering is ppular with cmmercial tmat, pepper, and meln grwers fr an early start t the grwing seasn. It prvides 2 F t 4 F f frst prtectin, prtects tender plants frm cld spring wind, and prvides warmer 722-2

The structure is easily pened during warm days and clsed fr cld nights. It wrks well with a 4-ft wide, raised-bed garden system. [Figure 3] Figure 3.

3 grwing temperatures inside the tunnel. Tunnels are remved when warm weather arrives and the danger f frst is past. Plastic Cvered Cld Frame Made with Cncrete Reinfrcing Mesh An easy cld frame structure fr a grwing bed is made with 4-mil clear plastic (plyethylene film) draped ver cncrete reinfrcing mesh. The structure is easily pened during warm days and clsed fr cld nights. It wrks well with a 4-ft wide, raised-bed garden system. [Figure 3] Figure 3. Cld frame fr a raised bed garden made frm cncrete reinfrcing mesh cvered with 4- mil plastic. Ntice the belt-like plastic straps, which hld the cvering in place. The cvering is slid between the straps and mesh t pen and clse. Pictured pen fr ventilatin n a warm day. The frame is cncrete reinfrcing mesh, available at hardware and lumber stres. This stiff wire mesh typically cmes five feet wide, in 50 and 100-ft rlls. A six-ft length is required t make a Qunset-type frame ver a fur-ft wide grwing bed. In trials, the lw and spreading shape was ideal fr trapping heat frm the sil during a frsty night. Cver the frame with clear, 4-mil plyethylene plastic. It typically is sld in 10 by 25 rlls. Fr a fur-ft wide raised bed bx, place a 3½-ft wide sectin n each side, verlapping at the tp. On a raised bed bx, staple the plastic t the sides f the wd bx. In sil bed applicatins, bury the plastic a few inches alng the sides. Hld the plastic nt the frame with small clips available at lcal hardware stres. Clthespins d nt hld in the wind. Anther methd is t use a series f 6-inch wide, belt-like plastic straps arching ver the frame (abve the plastic cver) and stapled nt the bx. Open and clse the cver by sliding it between the frame and the belt-like straps. Hld the plastic clsed at the ends with a rck r brick. [Figure 4] Figure 4. Clip hlds plastic n frame

During the day, the cvering MUST be pened, at least a slit, t prevent verheating. With just an hur f sun, temperatures under a clsed cver can quickly rise t ver 130 F!

On freezing nights, clse the cver cmpletely. On warm nights, the cvers may be left pen a crack. On strmy days with full clud cver and n direct sun, the cver may remain clsed. [Figure 5] Figure 5.

Nt nly will the cvers prvide frst prtectin, they als increase grwing temperatures fr early crp grwth and prvide prtectin frm cld winds.

4 During the day, the cvering MUST be pened, at least a slit, t prevent verheating. With just an hur f sun, temperatures under a clsed cver can quickly rise t ver 130 F! [Figure 5] On cl days, pen the tp a crack t prevent excessive heat build-up. On a warm day, the plastic can be slid dwn the side, ventilating and prviding crps expsure t the utdrs. On freezing nights, clse the cver cmpletely. On warm nights, the cvers may be left pen a crack. On strmy days with full clud cver and n direct sun, the cver may remain clsed. [Figure 5] Figure 5. Left: Cver must be pened at least a slit t prevent ver-heating. Right: Cld frame pictured clsed fr a cld night. Nt nly will the cvers prvide frst prtectin, they als increase grwing temperatures fr early crp grwth and prvide prtectin frm cld winds. In trials in Frt Cllins, Clrad, a plastic cver n a frame typically prvides 3 F t ver 6 F f frst prtectin. It wrks well fr cl seasn crps that are smewhat tlerant f frsty nights, and adds tw t six weeks r mre n bth ends f the grwing seasn. Fr warm seasn tmates and summer squash crps (being intlerant f a frsty nip), adding a small light inside the cld frame prvides even better frst prtectin. Adding Space Blankets On extra cld nights, placing an aluminum space blanket ver the plastic n the frame significantly adds t the frst prtectin. With the aluminized side placed dwn (twards the plants), a space blanket reflects 99% f the heat. They are readily available where camping gear is sld. [Figure 6] In trials in Frt Cllins, tpping a plastic-cvered, cncrete mesh cld frame with a space blanket prevented freezing when utside temperatures dipped t 0 F fllwing a sunny spring day. The space blanket must be remved each day t recharge the sil s stred heat 722-4

In Frt Cllins trials, ne 25 light string f C-7 (mid-size) Christmas lights per frame unit (fur feet wide by five feet lng) gave 6 F t ver 18 F frst prtectin.

5 Figure 6. Aluminum space blanket cvering a cld frame fr extra prtectin n cld nights. Lights fr Additinal Heat Christmas tree lights Fr additinal prtectin, add Christmas tree lights inside the cld frame. In Frt Cllins trials, ne 25 light string f C-7 (mid-size) Christmas lights per frame unit (fur feet wide by five feet lng) gave 6 F t ver 18 F frst prtectin. Lights were hung n the frame under the plastic and turned n at dusk and ff at dawn. Christmas lights wrk better than a single, large light bulb in the center by eliminating cld crners and edges. [Figure 7] Figure 7. Cld frame with Christmas tree lights fr additinal warmth. Space blanket with Christmas tree lights Fr the gardener really wanting t extend the grwing seasn, try Christmas lights plus a space blanket. One 25 light string f C-7 (mid-size) Christmas lights per frame unit (fur feet wide by five feet lng) with a space blanket n tp gave 18 F t ver 30 F frst prtectin in Frt Cllins trials

Wall f Water The Wall-f-Water is a cne-shaped ring f cnnected plastic tubes filled with water that surrunds a single plant, like a tmat, pepper, r summer squash.

6 Wall f Water The Wall-f-Water is a cne-shaped ring f cnnected plastic tubes filled with water that surrunds a single plant, like a tmat, pepper, r summer squash. [Figure 8] This device wrks n the chemistry principle f heat release in a phase change; there is a significant amunt f heat released as water freezes (changes frm the liquid phase t the slid r ice phase). A Wall-f-Water prvides frst prtectin typically dwn t temperatures in the mid-teens. It als prvides wind prtectin fr tender plants and grwing temperatures may be slightly warmer inside a Wallf-Water. They are helpful t get a few extra weeks head start n vine ripe tmates. Hwever, an extra early tmat may ut-grw the prtectin and the tps may be nipped back by frst. Bth cld air temperatures and cld sil temperatures are limiting factrs in early crp prductin. When using a Wall-f-Water t start early crps, warm the sil with black plastic mulch. Fr details n using plastic mulch, refer t CMG GardenNtes #715, Mulches fr the Vegetable Garden. In filling the Wall-f-Water, be careful nt t splash excessive water nt the sil. A wet sil will be bth slw t warm and dry in the spring. Mderately mist sils are best. Figure 8. Tmat in Wall-f-Water. Ntice use f black plastic mulch t warm the sil, anther limiting factr f early prductin. Als, nte the plant has grwn beynd the device and is nw less prtected frm frst. Authrs: David Whiting (CSU Extensin, retired), with Carl O Meara (CSU Extensin, Bulder Cunty), and Carl Wilsn (CSU Extensin, retired). Phtgraphs by David Whiting; used by permissin. Clrad Master Gardener GardenNtes are available nline at Clrad Master Gardener training is made pssible, in part, by a grant frm the Clrad Garden Shw, Inc. Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use. Revised Octber

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