GardenBot is an open source garden monitoring system. This site is a collection of tutorials for how to build things (like a soil moisture sensor), software for running GardenBot, resources, links, and more.
To get started, you will want to browse the How-To section to see what is required to build the various modules.
The ultimate goal of the GardenBot project is to be a complete garden monitoring and automation system. A key design consideration is to keep everything as easy as possible — especially for users new to Arduino and DIY electronics projects.