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Experimenting with Lighting

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[dropcap class=”kp-dropcap”]E[/dropcap]arlier in the season, I set up an experiment to see whether I could hasten flowering using far-red light at 730nm after dusk to flip the plants’ chemistry. The experiment was not successful, but I think that the results were inconclusive because the lights used weren’t intense enough.

However, I had inadvertently created another experiment that I mentioned in my last column. I had placed a 320-watt induction fluorescent light against the wall of the greenhouse, just over the plants, in the center of the garden. The light turned on each day in the afternoon for four hours as the garden phased into shade. It turned off hours before dusk, so all the plants in the room received the same length of photoperiod. However, the plants on either side of this light were powered only by natural light.

Last month I noticed that the flowers of the plants receiving the supplemental light were ahead of those of the side plants. Now, it’s the first week in September, one month later, and the plants are showing marked differences based on their placement, rather than on variety. The buds closest to the bulb and in direct contact with sunlight were the first to ripen. Buds on the same plant that received less light were a few days behind, but the side plants, which received no supplemental light, were two weeks or more from ripening.

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This outcome is consistent with other studies regarding DLI (daily light integral). It represents the total amount of light usable by the plant over a 24-hour period. The theory is that growth and maturity is dependent upon the amount of light the plant receives.

In this experiment neither the enriched light plants nor the controls were receiving the maximum light they could process, but the enriched light plants were receiving considerably more than the controls. Therefore, any difference in growth or maturity not variety related would be attributed to the increase in light of the experimental group.

The result was that the experimental group did grow larger and mature faster than the control group.
The result of this experiment has practical applications: Supplementing natural light with additional intensity from electrical sources increases the yield while shortening ripening time. The light can be used to supplement the whole garden in the fall, when natural light intensity is diminishing day by day. Increasing light to the shaded part of the garden, especially when the plants are maturing, is even more beneficial. Supplementing the natural light with light from induction fluorescents, white LEDs or metal halides adds brightness, but is usually not noticeable to casual passerby since all of their spectrums are close to natural light.

I’ve now harvested all of the plants that were under the lights. They are drying in the drying room. The plants that were growing without supplemental lighting are now maturing under the lighting. In the next few weeks they too, will be hung to dry and cure.

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TIP:

Time for fall planting

If you live in the lower third (latitude wise) of the country, where the sun is still intense in winter, you have greenhouse protection or an unobstructed south facing window, you can plant a fall crop.

Place clones in 6-10 inch pots. Use high quality enriched planting mix. Then place them in the sunniest part of the garden or greenhouse.

Because the plants are getting long nights they will immediately start to flower. They will stay small, single bud plants. In about eight weeks, they will be ready to enjoy.

Options:

If you give them supplemental light, they will grow bigger.

If you break up the dark period with bursts of light a couple of times each night during the dark period the plants will continue to grow larger. When you stop, the plants will start to flower.

If you extend the light period to 18 hours, they will grow faster and continue to grow vegetatively. As soon as the light period is decreased to 12 hours daily, the plants will begin to flower.

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