Watercress is semi-aquatic, having hollow stems that allow the plant to float on top of the water. The plant has a peppery flavor. I expect that it will do great in the hydroponics system.
Jan 7 = Day 0. Plants started from seed (Botanical Interests). Seeds were sowed in 1.5-inch rockwool cube in 2-inch net-pot. Seeds were tiny, pressed them into the top of the rockwool cube instead of putting them in the central hole. Moistened with dilute fertilizer solution: 1 mL (1/5 tsp) Dyna-Gro Liquid GROW 7-9-5, 1 mL pH Down per gallon of tap water. N-P-K (in ppm): 18-10-11. pH = 6.0.
Jan 11 = Day 4. Plant germinated, placed directly under a fluorescent light (2 ft. T8 bulb, 17W, 6500k) for 16 hours per day.
Jan 20 = Day 13. Installed plant into 0.5-gallon glass jar. Hydroponic solution composed of 0.5 gal tap water, 3 mL Dyna-Gro Liquid GROW 7-9-5. N-P-K (in ppm): 111-62-66. pH = 6.0. No pH adjustment required.
Feb 1 = Day 25. As the plants were getting long, they started hanging down the sides of the jar, and could not support themselves. Plants began to crimp at the base, resulting in wilting of the stems and leaves.
Growing in a jar is clearly not ideal for a plant like watercress. It would be better to grow this plant using a horizontal support structure, as described by Dr. Kratky in this paper or in this video. I will try to grow watercress again sometime in the future.