Quote:
Originally Posted by halfway
Straight 12 and 12. My last batch of soil lettuce was at 14/10 and bolted early. Couple folks recommended no more than 12 for the simpson. It looks like the basil is fine with those hours as well.
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From the research I've done, it seems that the amount of hours light won't have any effect on your plants bolting if harvested at the best time. Indeed, 24 hour light has been shown to increase yield/per/plant.
Here's one abstract of a study:
Title: Yield and quality of greenhouse lettuce as affected by form of N fertiliser and light supply
1. AuthorsZ. Premuzic
2. A. Gárate
3. I. Bonilla
Author Affiliations:
1.University of Buenos Aires, Argentina. Av San Martin 4453 (1417) Analytical Chemistry, Department of Natural Resources and Environment, Faculty of Agronomy Buenos Aires Argentina
2.Universidad Autónoma de Madrid Department of Agricultural Chemistry 28049 Madrid Espaă
3.Universidad Autónoma de Madrid Department of Biology. Faculty of Sciences 28049 Madrid Espaă
"Lettuce (Lactuca sativa) cultivar “mantecosa” with different kinds of light supply and different N fertilisation treatments was greenhouse grown. Three treatments were applied: two with N fertilisation: 1 – mineral fertilisation with 94 % Ca (NO3)2 − 6% NH4NO3; 2 – organic fertilisation with biostabilised compost and 3 – without fertilisation: control. Each treatment received two different kinds of light supply: 1 – 24 hours artificial light and 2 – no artificial light. Yield and nitrate content and vitamin C were determined in plants harvested at commercial maturity.
24 hours of artificial light supply improved yield and decreased nitrate content, but did not affect Vitamin C content. Both fertiliser treatments resulted in the same yield level. However, mineral fertilisation resulted in a higher concentration of nitrate in lettuce whereas vitamin C content did not differ significantly between all treatments."
Yet conflicting statements are in this report:
by Sherry Rindels, Department of Horticulture (Iowa, USA)
"Producing a successful lettuce crop can be a challenge for home gardeners. Weather is the main problem. All types of lettuce (crisphead, butterhead, leaf or bunching, and romaine or cos) require cool, moist growing conditions. Daytime temperatures of 70 to 75 and nighttime temperatures of 55 to 60 are ideal. Adequate supplies of moisture and
nutrients are also important. Lettuce requires one inch of water per week. As with other plants, gardeners will need to water when Mother Nature doesn't supply sufficient rainfall. A complete fertilizer, such as 10-10-10, applied to the garden prior to planting should be adequate for successful growth.
Bolting is a common problem experienced by lettuce growers. Bolting is the undesirable formation of flowers and
seeds. Bolting destroys the flavor of the leaves by making them bitter and tough. It is caused by high temperatures, long periods of high light intensities, and drought. Lettuce has an internal counter that keeps track of the number of daylight hours the plant receives. Once a critical number of hours are received, the plant sends up its flower stalk. The exact number of hours varies from cultivar to cultivar. Apparently, lettuce goes through four distinct stages of growth; juvenile/vegetative, adult/vegetative, adult/intermediate, and adult/reproductive. The plant can handle environmental stresses quite well when vegetative. However, once the intermediate stage is reached, environmental stresses, such as high temperatures or drought, will cause the plant to bolt.
Gardeners can reduce the tendency for bolting in various ways. Lettuce can be started indoors under
lights to give them an early start and then planted outdoors while temperatures are still cool. When growing lettuce seedlings under lights,
do not leave the lights on for more than 12 hours because lettuce needs short days to grow."
(end of quotes)
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It seems that the intensity of the light is the determining factor in these two seemingly conflicting reports.
In the second study above, it discusses using the four stages of growth to determine harvesting times:
lettuce goes through four distinct stages of growth;
1. Juvenile/vegetative
2. Adult/vegetative
3. Adult/intermediate
4. Adult/reproductive.
As long as the plant is harvested *prior* to it's entering the Adult/Intermediate stage of growth, bolting would be avoided and the plant would grow faster and provide more yield if kept in 24 hour lighting.
For larger plants that are kept growing into and beyond the vegetative growth cycle, the decreased light hours would be a factor in it's bolting, along with humidity, heat and drought.
I would set up the plants for low levels of 24 hour/day light, (studies show that the low intensities don't effect vegetative growth much), and plan harvests on the last days of vegetative growth with short crop cycling to optimize efficiency.
That way, yield is increased, bolting is eliminated and lighting efficiency is maximized by using the least intensity but longest hours.
Mind you, for me, this is just theory based on studies. I've yet to grow indoor lettuce, so my tests this coming year will show the real results.
I'm pretty confident that these folks know what they're doing, and have reported accurately. I'll have to let you know in a few months.