Table i. Summary of temperatures under different coverings during two winters in Deerfield, NH. 



1. Minimum and maximum temperatures under each type of covering during the entire winter. 



2. Average 24-hour temperature. 



3. Average daily range from minimum to maximum temperature. 



Table 2. Average plant vigor rating" after overwintering under different coverings during 1997 and 1998 in DeerBeld, NH. 



1.1= dead, 2 = stressed or weak (sufficient damage to affect market value of the plant), or 3 = healthy. 

 2. Assumes that Lobelia and Phlox would have completely survived in the unheated greenhouse in 1997-98. 



media and coverings. 1998-99 was 

 a cooler winter than 1997-98, with 

 the unprotected media dropping to 

 -8F in 1998-99, compared with 2F 

 in 1997-98. 



All of the coverings were very ef- 

 fective at raising the minimum soil 

 temperature. Minimum soil tempera- 

 ture, even under the single foam 

 blanket, was 27F higher than unpro- 

 tected soil temperature in 1997-98 

 (29F compared with 2F), and was 

 32F higher than unprotected soil 

 temperature in 1998-99. During 

 both years of trialling, single foam, 

 foam and fleece, and unprotected 



AUGUST/SEPTEMBER 1999 



greenhouse environments had very 

 similar minimum, maximum, and 

 average temperatures. Minimum and 

 average temperatures in the heated 

 greenhouse were warmer than in the 

 other environments. 



The graph of temperatures over 

 time (Figure 1) for 1997-98 shows 

 that all coverings were effective at 

 maintaining stable temperatures at 

 around freezing even though unpro- 

 tected soil temperature dropped be- 

 low 1 5F on five different occasions. 

 The foam and fleece had less of a 

 temperature range (overall maxi- 

 mum, overall minimum, and daily 



range), compared with the single 

 foam blanket, and would be desir- 

 able to reduce freeze/thaw cycles. 



EflFect of Coverings on Plant 

 Survival: 



Adequate snow cover can act as an 

 insulator protecting hardy plants 

 from fluctuating temperatures (Perry, 

 1997). However, partly because un- 

 protected containerized plants lacked 

 consistent or adequate snow cover in 

 both years tested, they were suscep- 

 tible to cold temperatures that se- 

 verely reduced their survival. Plants 

 that had did not survive without 



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