When growing the vegetables themselves, my students (kids) took more of an interest in vegetables. They continue to grow in their appreciation of food and the influences they have on your body. Understanding the effects it has on the brain and the gut has come from several years of learning and knowledge that all stemmed... (pardon the pun) from their gardening experience.
My children have a new appreciation of the labor involved in providing care for something and have a new appreciation for all life. This has come in handy when explaining the importance of gratefulness, love, and compassion for others. All these experiences are connected. Plus, experiencing creation through the lens of child gives new meaning "life" itself.
The science goes without mention, but science inquiry was behind it all. They didn't learn it from a book they experienced it; failure and success, all through their own observation and experimentation. Learning is a constant, and inquiry is the irreplaceable foundation of knowledge.