The 2009 ASHS Annual Conference

Red lava rock has the characteristics of an excellent hydroponic media and has been used extensively as a growing media in Mexico. However, little information is available in the literature on plant production in this substrate. Four herbs, rosemary, thyme, mint, and basil, and one cut flower crop, sunflower, were grown under five watering regimes in two separate experiments to study water use and species interaction in a red lava rock media. In order to create a hydroponic media optimum for plant growth we designed two substrates with aeration of 13.6 and 35.3 percent and container capacity of 16.5 and 11.0 percent, respectively. Plants were watered three, twice, once, every other day, and twice a day alternated by once a day, with a modified Hoagland’s solution at 120% of container capacity. Data on fresh weight, dry weight, plant height, number of stems, and in the case of basil, number of leaves, were collected over a period four months for each harvest of the crops under investigation. In this period basil, thyme, rosemary, mint, and sunflowers were harvested 4, 2, 2, 3, and 2 times, respectively. The highest average fresh weights per harvest, at the optimum watering regime and substrate combination ranged from 237.2 grams for basil to 86.8 grams per plant for sunflower. The highest average dry weights per harvest, again at the optimum watering regime and substrate combination ranged from 34.0 grams for basil to 15.4 grams per plant for sunflower. Watering regime showed a clear effect on fresh weight and dry weight of basil, mint, rosemary, sunflowers, but not thyme. In those crops that showed an effect of watering regime on fresh weight and dry weight, a general trend was observed towards lower weights correlated to less watering. However, in most instances no differences were observed between watering three and two times a day or watering once day compared to watering twice a day alternated with once a day. Despite the severe restrictions on growth as measured by fresh weight and dry weight due less frequent irrigation, a less significant effect on height was observed in our experiments. Based on our results we conclude that watering on average twice a day in a red lava rock media designed for hydroponic production (high aeration) can result in good yields of basil, mint, and rosemary, and sunflower. Thyme can be successfully grown with only one fertigation application per day.