Seaweed extract benefits petunia, tomato transplants

Seaweed extracts are used widely in agriculture and horticulture production systems. Benefits of the extracts can include early seed germination and establishment, improved crop performance and yield, increased resistance to biotic and abiotic stress, and enhanced postharvest shelf life. A study in the August 2015 issue of HortTechnology determined the effects of rockweed extract, applied as a drench or foliar spray, on plant growth and drought tolerance of tomato and petunia transplants.

According to study authors Yuqi Li and Neil Mattson, rockweed (RWE) concentrate contains macro and micronutrients, amino acids, vitamins, cytokinins, auxin, and abscisic acid-like growth substances, which affect the properties of growing media, plant growth, and crop yield. To determine if rockweed could be beneficial to petunia and tomato, the researchers tested RWE applications on transplants in greenhouse experiments at Cornell University.

"In this study, drenches significantly affected substrate pH and EC and several measured elements. RWE drench increased substrate Na⁺, K⁺, Cl⁻, and NO₃⁻−N. The opposite trends were found for Ca²⁺ concentrations," the authors said. Analyses showed that RWE foliar sprays were not effective for improving drought tolerance of petunia and tomato, whereas substrate drenches significantly improved drought resistance of both.

"Results of the study suggested that RWE substrate drenches at 5-10 mL·L⁻¹ are appropriate for the improvement of postharvest life of petunia and tomato transplants; however, monitoring of substrate pH should be done," said the authors. They added that rockweed foliar sprays can improve growth of both plants.