A number of years ago, a lighting engineer, who was also an avid home gardener, decided to grow tomatoes completely under artificial light.
He constructed a large, enclosed Quonset—a lightweight, prefabricated structure made of corrugated, galvanized steel with a semicircular cross-section—and installed the latest in lighting devices to provide the light intensity and spectrum he thought would be required by his tomato plants.
He wanted me to install the hydroponic growing system I had been using for the growing of greenhouse tomatoes. He had made a number of visits to my greenhouse and was impressed with the yield and quality of tomatoes I was producing, as well as the water and nutrient element efficiencies the hydroponic growing system provided1.
I installed my hydroponic rooting system in his Quonset structure. He selected three greenhouse tomato varieties that were in common use and one that I was growing. The plants grew well but they did not produce many flowering stems, and few fruits were being set and produced. He had all the measuring devices he needed to determine light intensity and spectrum quality were both optimal.
There was no natural light coming in as there is with a greenhouse. He made a number of changes in the lamp types and made changes in their configurations. I also made changes in the nutrient solution formulation to put stress on the plants to hopefully force them into a more reproductive state.
The tomato plants continued to grow without generating many flowering stems. After about six months of making changes to the lamp types and their configuration, but without success, he gave up the project.
We talked about why the tomato plants failed to flower, thinking mainly that there was something missing in the lamp characteristics, either their intensity or spectrum distribution, which neither he, nor I, was unable to identify and correct.
Several years later, I decided to grow outdoors the tomato varieties I was growing in the greenhouse. To my surprise, the plants did not grow as vigorously as they did in the greenhouse.
In addition, fruit yield and quality were poor. I thought about the lighting engineer and his experience. Maybe it wasn’t the lamp types and their light spectrum that were the reasons his tomato plants grew without producing flowering stems. Perhaps it was the tomato plant variety that was the significant factor.
Greenhouse tomato varieties are bred and selected for growing under greenhouse conditions, which provides filtered light, while those for outdoor production are selected for growing in outdoor conditions in unfiltered light. That could be the significant difference. Evidently, there was something in the outdoor lighting characteristics that was not compatible to the greenhouse tomato varieties. What that something might be would make for an interesting research project.
When growing plants under artificial lighting, variety breeding and selection must be done for such conditions. Trying to have a plant variety grow well when bred and selected under different light conditions can be a reason for poor plant performance.
Now, I wonder if my lighting engineering friend would have been successful if the variety, or varieties, he selected were adapted to the light conditions he had established. I believe that in his experience, it was not the lighting conditions that were at fault, but the selected tomato varieties that did not conform to the lighting conditions he had established.So, what’s missing from this equation? I believe it is plant varieties that are bred and selected for the lighting conditions being generated by the grow lamps in common use today. If growing plants under artificial lighting conditions is to be successful, the grower needs to have varieties that are adapted specifically to these lighting conditions. Otherwise, the grower must accept that the plant growth that is obtained is possibly limited by the genetic characteristics of the selected variety, which are not able to conform to the established lighting conditions.