I will use the pages on kimbriggs.com to explain the how and why of the farmdens database basic overview. For a working sample of the first rev of the PHP - MySQL application, you can visit the domain itself:

farmdens.com Homepage

farmdens schema

The picture link above leads to a larger scan of the design of the farmdens database. This is a very generic design that is best described by "Events having items and actions in space-time". Many of the "look-up tables" would need to be populated for your particular needs, which could go well beyond the scope I used of a garden.

You can Contact Kim Briggs if you want explanations, the install scripts, or want to work on developing it further.