OpenFarm is a free and open database and web application for farming and gardening knowledge. One might think of it as the Wikipedia or Freebase for growing plants, though it functions more like a cooking recipes site.
The main content are Growing Guides: creative, crowd-sourced, single-author, structured documents that include all of the necessary information for a person or machine to grow a plant, i.e.: seed spacing and depth, watering regimen, recommended soil composition and companion plants, sun/shade requirements, etc.
Other use cases: a mobile app for home gardeners, Google providing “One Box” answers to search queries such as “How do I grow tomatoes?”, smart garden sensors, automated farming machines.