Efficient use of solar and ground heat enables
raising of crop in plastic greenhouse when ’
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()lltSl(l€ t€IllI)€1‘2,ltlll`€S RPC (lOWI1 to 5 F.
Lettuce Grown -— No Heat Cost
By FRANK li. BORRIES. JR.
Vegetables need heat—~natural or artificial—to grow air space between the two sheets which acted as a heat .
bttt Kentucky ,\gricultural Experiment Station horti- cover. (See drawing on opposite page.) _
cttltttrists had surprisingly good results: this year with The whole greenhouse was about 5 feet high.
a plastic field greenhouse that got a crop of` lettuce though limmert now recommends a height of 5% to
simply by trapping solar and ground heat and con- (5% feet. The roof covering consisted of a dottble
serving it. layer of plastic, one fyi-lllll thick inside the frame and
li. Nl. limmert, who conducted the trial, found that another 2 mils thick outside. l·l is rafter spacing origi-
once, when the temperature outside the house was nally was —f feet apart; however. this retptires a heavier {
onli Fi de trees l·`., the tetn >eratttre under an inner >lastic, the ·f—mil thick toe. Two-foot raf`terin¤· can
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floor covering of plastic was 38 degrees l·`., or 35 de- use the 2-mil thick plastic, Emmert says.
trees hi ther. He used no artificial heat at all. Instead, he utilized
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The plastic ground cover inside the greenhouse con- sunny days (for solar heat) for the initial warming:
sisted of two sheets of 2%-mil thick plastic stretched compacted the soil by watering, which allowed trans-
fer of` heat much better than loose soil; and took ad- _
· . ‘‘‘     - .  -~¢=     ,,, .,.·.· , ..·_ I _,_.... .     .._, _ __,_,,   vanta ·e of >‘rottnd heat arisin ‘ from de >ths of a foot
. awc -   .r... 1 -.-. V -.... . V to rvzr V.V··~V Ii. V     ,-..t..,- .V./ . V. g h c
` . i»V; v ·t ·tI»"/-‘ lt ’ [til; 'f’·'VV‘·`4:l i’'. EMI,. ·l»€V?§>r¤*‘- LA   J   f     » . I I,I‘ I ., I , . I I A. . , , I · I , —
      . I ~r__   I   _.:_   ,_:=_—_= ;   up ant c t oosc, ttc gtount 1(att stayet in Llc
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— lt/V s·i5*~` y~     (       jgj ..·- 1 —_-=  gxricgg  -,_ ground. \\’hen the soil was compacted bv watering, ;
I f/pt ‘ t ~ . .   if _:     _,,_     ' _ ’ _ _ ‘
  »»._   _     :,··-;   the heat filtered through and heated the air nnme- .
V. »   Y    ‘ V  I-   ;’=--¥     - - -
‘— · , · V   ~_,·   —.         ._-_     dtatelv above. Loose soils keep the ground heat from
  ` I [   — r  #r,J\.;e ”‘“`°`f“ "· —   ’ _ `
`hse °°```   `¢``` ·¢"   .   escaping. l·`or cxznnpfe, in the winter observers have Q
`     IT· noted that a plowed field will keep its snow cover
  c V ~ V" °-‘ ~ ·
6   N M. v   ¤VV longer than a compacted field for the same reasons,
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   sis     =»‘   est.   _ V I ~ »-=—- —   I \   ==¢ gi.
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 ?‘$’       Y ""‘~§`   .  ew » .  Q ‘   2*; s . V, l'‘’ * i*#%:Q?;;- V.,_ _
 +,:3  §_ _¤§§_— ¢=? § * `   js ` .-X; Ml" its *5 sl; ki;.  lf X V   \ `\   ,
Ilorticulttirtst limtnert inspecting evidence of possible snow   E;  * ` _ it R`? c \  
damage to plastic field greenhouse similar to one in which   _       V ¤ ‘. iii
lettuce was produced without use of ·trtifici·tl heat T ~   iiil * " ` T ·` hg`? ¥   r -.4 \"
  ···—        lr    l    
_ _ _ _ 4 ~·¥§ ,...:   -V·~     -·        > 2
on a ltght wire frame about IS inches above the { _ `   .  i_`*         { e.
ground. f`he cover could be lifted for inspecting the i . ,   ·~i il.    `    " ~*“ ii f   A
I I I I _ _ _ ‘_ __' . __,__Me I!   vaglll &n {M 4%,, v__V   I  —.V,  ,2;;  »V  
crop oi liatxesting. .\n aisle was left down the middle   _ ,» · ,  “·’.   ~.-`=,., ` "_j,;-#·_ Q
ol the house for access. lhe top sheet of the ground _ _ _ _ __ _ IV
_ _ _ _ . . ‘ Lettuce growing in a plastic greenhouse without artthcial `·