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Earthbox Lighting Trial Data
Sarah Watts & Alyssa Ralph
Difference in plant quality/ quantity between a four bulb, high efficiency, T5,
28 watt light and two bulbs of the same light. Do lemon gem, parsley, and garlic chives grow better under a four bulb, high efficiency, T5, 28 watt light or two bulbs of the same light? This investigation attempts to understand which of the two lights has the maximum production out of our earth boxes, compared against the purchase and energy cost of each. Problem: Two bulbs are significantly more efficient and inexpensive than four bulbs, however, are they just as effective for indoor herb growth in a classroom setting? In other words, although two bulbs are cheaper than four, would having more lights increase the amount of product produced by double? Background Info: Mr. Korotash indicated that he had experienced some success growing plants in the small earthboxes using only a 2 bulb fixture, our experiment set out to determine whether or not a two bulb fixture is just as productive as a 4 bulb fixture-‐ If not, are the efficiencies significant enough to make a difference? Experimental Design: The following experiment was conducted using two independent large earthboxes, one attempting to grow herbs when placed under a four bulb, high efficiency, T5, 28 watt light, and the other under two bulbs of the same light. Many precautions were put in place ensuring that the variables remained constant between the two boxes, with the exception being the number of bulbs. We followed the exact directions on out earthbox instruction kit. -‐Each earthbox can hold a maximum of three gallons of water at a time and 2 cubic feet of a chosen growing material-‐ this case being potting mix. -‐We used Sunshine professional potting mix (75.85% Canadian sphagnum peat moss) -‐At the start of the experiment, we only watered our plants every few days. Now that they are well and flourishing, we fill the earthbox with water as often as we can in order to ensure optimal water consumption is being vitalized. -‐The lights in the classroom are left on 16 hours a day, from 7a.m. to 11p.m. They have been running since the 6th of November.
-‐ Lights were approx. 0.5ft away from top of the vegetation. -‐ Plants used: Garlic chives, parsley, and lemon gem (marigold) -‐ Earth box was split evenly into three; herbs were seeded directly across from one another, on either side of the box. -‐Blue box was placed under a two bulb fixture, whereas the green box was placed under a four bulb fixture.
An image of the Earthbox’s growing environments. 2 bulb on the left and 4 bulb on the
right. Results: November 6th 2014: Seedlings are first planted November 12th 2014: Mold has sprouted on blue bin, will be treating with hydrogen peroxide spray. Lemon gems and garlic chives are both now growing, but still no signs of parsley. After six days, we are now taking the thin plastic wrap off the tops of both bins.
November 24th 2014: Parsley has sprung on both bins now; green bin’s is slightly taller. November 26th 2014: Observed that the tops of the garlic chives are dried out and dis-‐colored, which I believe is normal seeing this same case is apparent on the blue box as well. Both the parsley and lemon gem are growing as a steady pace, are short, stocky, and so far have not been in need of thinning. White “flakes” have begun to form around the middle of the dirt, I will take note and check back on it Monday. The lemon gems are fuller and much darker on the green box. December 10th 2014: Green box’s water is now filled to maximum capacity. Also thinned parsley slightly on both boxes. December 11th 2014: Raised light on both hydroponic boxes approximately 2 inches so that the chives are no longer growing into the light bulbs. Partner and I observed
Lemon gem has just started to sprout.
that the foliage in the Earthbox with 4-‐bulbs is prominently taller and fuller than that growing in the 2-‐bulb setting. December 15th 2014: Parsley and lemon gem have grown exponentially (nearly 2x) over the long weekend. Whereas, garlic chive growth has been steadily rising throughout the past few weeks. Noted apparent algae growth on blue bin. December 17th 2014: Cucomorous mites have been added to both boxes, as there is a rise in the thrip population, only minor damage has been distinguished. January 5th 2015: Came back to class only to find bountiful herbs on both boxes. Lemon gem has started to bloom beautiful yellow flowers on green box (4 bulb) whereas blue box’s (2 bulb) lemon gems are still budding. Blue box’s garlic chives have been harvested and cut to approximately 2 inches. The garlic chives growing under the four bulb light appear to taste much more appealing to that under the two blub light; whereas the parsley is the opposite-‐ as they taste much better from the blue box (Lemon gems do not taste of anything, they are a garnish) Both of us have noticed that the blue box’s herbs are much less saturated compared to that growing in the green box, this is especially visible with the parsley.
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Garlic chives Parsley Lemon gem
Height in centimeters
January 5th 2015
Green box
Blue box
Analysis: A 2 bulb fixture would indefinitely be more inexpensive up front, but if you want to produce fuller, more tasty herbs, a 4 bulb fixture would be the better option. It is evident that for double the cost of running, additional lights in this instance do, in fact, produce more than double the harvest. In order to compare total energy costs, we will set up a simple equation, where $0.07545 is the current cost per kilowatt-‐hour in Alberta: Green box (4 bulb): 28watts x 4 bulbs = 112 watts ÷ 1000 = 0.112 kilowatts x 16 (hours it’s on a day) = 1.792 kwh/day x 61 days = 109.312 kwh/61 days… 109.312 kwh/ 61 days x $0.07545 = $8.2475 Blue box (2 bulb): 28watts x 2 bulbs = 56 watts ÷ 1000 = 0.056 kilowatts x 16 (hours its on a day) = 0.896 kwh/day x 61 days = 53.009 kwh/ 61 days… 53.009 kwh/ 61 days x $0.07545 = $3.9995 *Evidently, this information only spans a 61 day trial, my research suggests that the bulbs used should be replaced approximately every year to maximize efficiency. Total amount of water blue bin consumed over duration of experiment: 20 liters Total amount of water green bin consumed over duration of experiment: 24.5 liters Conclusion: Parsley, marigold, and garlic chive production appears to be much more efficient when grown under a four bulb fixture as compared to that of a two bulb fixture in a classroom setting. While on the other hand, a 2 bulb fixture cuts the energy costs in half, and in doing so, it becomes the more environmentally sustainable choice. Evaluation: -‐On the first day of the experiment, the class ran out of the root seller potting mix, blue bin (2bulb) had to resort to a different one than what was used on the neighboring green bin (4bulb) -‐Few times near the beginning of the experiment, we both forgot to write down the amount of water we were adding to our boxes on occasion. With that being said, total water amounts may vary slightly. -‐Strive for a more thrip-‐free environment next time. -‐Trim plants more often and/ or move lights up higher, farther away from the canopy of the herbs. -‐Measured and compared the heights of the three plants more often.