This is a difficult question to answer with clarity. The current administration of the National Organic Program continues to allow the certification of hydroponic operations despite the recommendation from the National Organic Standards Board that clearly states it is not compatible with organic production.
The United States is one of the few countries that allows hydroponics to be labeled organic. Mexico, Canada, Japan, New Zealand, and 24 European countries (including Holland, England, Germany, Italy, France, and Spain) all prohibit hydroponic vegetable production to be sold as organic in their own countries. This means “organic” hydroponic producers in other countries are often growing exclusively for a U.S. market.
Presently, the vast majority of the “hydroponic organic” produce sold in the U.S. is grown in Mexico, Canada, or Holland.
We would recommend lettuce grown in natural soil with sunlight for maximum nutrient density, but of course, all things considered (seasonal availability, quality of the product, shelf-life, and cost), hydroponic lettuce is certainly a viable option.