... the greens were grown organically. Since they’re not pumped up on synthetic nitrogen, the cells of these slower-growing leaves develop thicker walls and take up less water, making them more durable.
And, I’m convinced, tastier, too. When I visited Greenways Organic, which grows both conventional and organic tomatoes, I learned that the organic ones consistently earn higher Brix scores (a measure of sugars) than the same varieties grown conventionally. More sugars mean less water and more flavor. It stands to reason that the same would hold true for other organic vegetables: slower growth, thicker cell walls, and less water should produce more concentrated flavors. That at least has always been my impression, though in the end freshness probably affects flavor more than growing method.
Source: The Omnivore's Dilemma: A Natural History of Four Meals (Large Print Press), Pages: 176
Contributed by: HeyOK