Foliar Spraying of Aqueous Lavender Extract: A Cost-Effective and Sustainable Way to Improve Lettuce Yield and Quality in Organic Farming

In recent years, a significant increase in the market availability of products with a phytostimulant effect on plants has occurred. However, these products are not always low-cost, and their effects on crops are not always reproducible. In this study, an alternative use of lavender, already known for its antimicrobial activity, is proposed: an aqueous extract from self-produced lavender (Lavandula angustifolia Mill., var. Hidcote) flowering tops was tested for its phytostimulant activity on lettuce (Lactuca sativa L., var. Bionda d’estate) cultivated under organic farming management. Lettuce plants were planted in an open field on a private farm (in the Lazio region, Italy): lettuce plants were treated weekly for two months with lavender aqueous extracts while control plants were sprayed with water. Results showed that treatment with lavender extract enhanced fresh edible production and dry biomass (12.08% and 15.09%, respectively) in lettuce plants, as well as leaf area index (28.01%) and photosynthetic efficiency (increased SPAD). At the same time, an increase in mineral content was observed: compared to the control, a 30.46% increase was observed for N, 31.10%, 35.52%, 36.19%, 47.51%, 48.11%, and 91.44% for K, Ca, Mg, P, Mn, and Fe, respectively. All these factors contribute to enhancing the commercial and nutritional quality of lettuce, as well as strengthening its self-defense and extending its shelf life. Results of this study showed that lavender aqueous extract exhibits phytostimulant activity and could be a useful product for obtaining higher yield and better nutritional quality of lettuce in organic farming.