Q: How many hours a day should I burn my lights?

A: There is no one best way to light plants: It depends on the type of plant, the kind of plant (species), and exactly what you want the plant to do. The typical rule of thumb for flowering plants is to run a 16 to 18 hour light cycle then 6 to 8 hours of dark time, during the vegetative stage. Then at the Bloom stage, switch to 12 on/12 off. It is also typical to run a Metal Halide during the Vegetative stage then switch to a High Pressure Sodium Light during the Bloom stage.

Q: What happens if the lights burn 24 hours a day?

A: The plants will grow. After about 16 or 18 hours in most plants, though, growth levels off. So if you turn off the lights for a few hours, you can save some electricity and not really affect growth. Plants often use dark time to build up Florins which are hormones plants use to bloom. This is why the light is often cut back during Bloom stage.

Q: If the Florin hormones need dark time to build up, can I burn a High Pressure Sodium Light 24 hours a day to keep lettuce from bolting and going to seed?

A: No., we've tried it, but it is another great theory shot down by the facts.

Q: Do you have any tips for growing both lettuce and tomatoes under the same light at the same time.

A: The light cycles and color of light of vegetative and blooming plants are referred to in most books as completely incompatable. Unfortunately for the theories, I have known other people beside myself who have been able to pull it off. The first requirement is to let go of the notion of perfection on earth; the perfect head of lettuce lives only in Plato's Cave--not in your garden. The tomato wants a cycle of light and color to induce blooming. Inducing letuce the same way will only encourage the head to bolt (go to seed). Tomatoes like very bright light and use a lot of nutrients; lettuce can get bitter with the same conditions. Using a mixed spectrum bulb is generally the easiest way to light the plants, but using multiple lights, shining differently on different kinds of plants is better. The tomatoes require more attention, and if there is a single light source, it should be centered on the tomato with the lettuce further around. The lettuce also likes it cooler and some red varieties will not show red without the coolness. Good luck, and if what you are doing does not work out, try it a different way.

© 2000-2003 K.Kelly and 3R Lighting