The split-night regime refers to lowering the minimum temperature of a greenhouse from 60 F (15.5 C) to 45 F (7.2 C) for 8 hours after 10 pm. We calculate that this scheme saves about 20% on fuel in the winter in Connecticut.
The temperature reduction does not appreciably slow either the growth rate or the development of tomatoes or Easter lilies. Our physiological studies of tomato plants suggest two reasons why plant growth is so little affected by this energy saving technique.
First, plants subjected to a repeated nightly drop in temperature do not show lingering inhibition of photosynthesis, translocation, or car- bohydrate metabolism the following morning.
Second, to compensate for the inhibition of physiological processes during the cool part of the night, plants subjected to split-night temperatures move sugars more quickly out of the leaves and stems during the day by degrading their starch reserves faster. This second phenomenon becomes especially evident during fruit production when more efficient translocation from the leaves is necessary for rapid fruit growth.
These physiological studies suggest that economic production of many crops will benefit from the split-night regime.Split Night Temperatues in a Greenhouse