If you are interested in seeing what is going on with your garden this Garden Monitor Project is something you should take a look at. It is using a Picaxe microcontroller and has an interesting home brew communication process. All of the schematics and source code are also provided.
"One day we had a good hard rain and I could see it the graph of the data; the surface temperature suddenly dropped, the light intensity dipped, the humidity rose, and the three inch moisture sensors indicated an increase. Later that day I was on the phone with my girlfriend and she said it had also rained early in the morning (I must have slept through it;) I looked at the data again and there it was… now that I knew what to look for I could see from the data that it started raining at about 05:10 in the morning. That’s when it struck me that this thing really does work!"
http://hackedgadgets.com/2008/07/06/garden-monitor-project-using-a-picaxe-microcontroller/