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Growers generally have several greenhouses, or one greenhouse 

 with sections. A greenhouse or section o£ a greenhouse may be 

 either heated and illuminated, heated, heated but started on a 

 different date in each greenhouse or section, or non-heated. Two 

 or more of these procedures are generally followed to spread the 

 harvest season. 



In the early-house or section, heat is started about January 

 10th and the plants are illuminated because natural daylight is 

 too short for the development of long flower stalks. Gas (usually) 

 or oil is used for heat. It is risky to force grov;th earlier than 

 the beginning of January because of possible reductions in yield 

 and fruit quality due to low light intensity. 



Fortunately, the illumination period can be other than at the 

 end of the natural day, because electric rates are higher at this 

 time than at night. In fact, growth response is greater from short 

 periods of illumination at night than from a continuous period of 

 illumination at the end of the natural day. Illumination for 15 

 minutes each hour from 11:00 P.M. to 7:00 A.M. is sufficient and 

 is practiced. Eight to 10 watts of light per square yard is suf- 

 ficient to form long leaves and flower stalks. However, the light 

 intensity is too low to produce growth comparable to that obtained 

 during the day. Light on a clear winter day is about 100 times 

 brighter than that supplied by the artificial light. Thus, even 

 when illumination is used, the plants need the duration and inten- 

 sity of daylight for the manufacture of food and to produce vigor- 

 ous growth. The artificial light does have an influence on the 

 utilization of daylight. Early, heated but non-lighted plants have 

 leaves with short stalks whereas early, heated, illuminated plants 

 have longer stalks and larger leaves. Thus, because of a greater 

 photosynthetic surface, artificially illuminated plants produce 

 earlier and higher yields than non-lighted plants. 



Harvest of early, heated, illuminated plants starts in late 

 March. The berries are picked at least twice a week into aluminum 

 boxes. On April 2, 1975, growers received $1.29 to $1.71 per box 

 containing 0.44 pounds of strawberries. A week later, due to in- 

 creased supply, growers received $0.73 to $1.06 per box of berries 

 of the same quality. 



Varieties differ as to when artificial light is no longer 

 necessary in a heated greenhouse. Some varieties can be forced 

 in early February without illumination. Thus, in February, plants 

 may be grown in either a heated, non- illuminated greenhouse or a 

 non-heated house. The plants develop somewhat more quickly and 

 fruit earlier in a non-heated greenhouse than in a cold frame. 



