test results from trying different growing media for lettuce
So since I eat salad very frequently I started gardening for the very first time several months ago- growing my own hydroponic lettuce . Since I get no sunlight and rely on grow lights, I wanted to maximize the efficiency so each head of lettuce wouldn't cost me too much. And since I'm a dorky scientist, I ran various tests comparing different methods. Since this took me a while and it might be useful to others, I wanted to share my lettuce growing results trying different types of grow plugs.
Equipment & Methods:
1) Containers were 1 gallon translucent polypropylene food storage containers (http://www.webstaurantstore.com/4-qt-white-square-food-storage-container/407S004PP.html), spraypainted on the exterior to block out light, except for a little strip so I could monitor the nutrient solution level (see picture for example)
2) I drilled a hole in the lid for a 2" net pot at the top, with the grow plug dropped in. Since the lid wasn't opaque, I put a sheet of tin foil on top to minimize the light exposure to the roots. I grew 12 heads of lettuce, using 3 each of 4 different grow plugs, listed below along with around how much they cost each for me (bought in bulk in amounts 50-100):
Rapid Rooter ($0.32)
Quick Start - these are similar to Rapid Rooters, not sure which company makes them ($0.29)
Sure to Grow ($0.07)
3) Nutrient solution used was 1 tsp each of General Hydroponics Flora Micro/Grow/Bloom, in 1 gallon tap water, making 7-6-11.
4) Growing method used was the passive non-circulating method proposed by Prof. BA Kratky at U. of Hawaii (see: http://www.ctahr.hawaii.edu/oc/freepubs/pdf/VC-1.pdf). This is basically deep water culture, without the air pump.
5) Three seeds of Salad Bowl lettuce (http://www.ferry-morse.com/product_detail.aspx?id=7485) were planted in the grow plug, about 1/4" deep, and thinned after around 1 week.
6) The light fixtures used had four 23w T5 flourescent bulbs (6500K), and was on for 15 hrs/day. Six lettuce plants were grown under one of these fixtures. The bulbs were kept around 2" above the top of the leaves.
7) Ambient temp & humidity was 65-75 F, 55-70% throughout. Temperature a few inches under the lights was 5-10 F higher.
8) Harvest was exactly 35 days after planting the seeds. Each head was cut off flush against the top of the grow plug, and weighed immediately after harvest.
Results (weight in ounces):
Sure to Grow:
2.86 (developed a disease)
2.12 (had a problem w/ the nutrient solution level lowering too fast)
6.10 (harvest at 34 days instead of 35)
So, although it's a small sample size, it seems like Rapid Rooters had the best effect on lettuce growth, with all the other types of grow plugs being equal.