Most of the effort in the gardening goes to keeping plant soil moisture at right level. Human cannot always be there and check it all the time. This is why in most cases moisture sensors are used that alert when plant needs watering. You can find cheap ready made solutions that beeps when there is water needed, but also there are more complex sensors with wireless data transfer. Wireless data is gathered in to nice receiver which can be hung somewhere inside. You can get those for about $10. So Ray decided to dig in to those and see if wireless sensors can be used as generic sensors for interfacing with Arduino or Raspberry Pi.
He found that Springfield 91746 Digital Soil Moisture Meter and Freeze Alert sensor communicates at popular 433MHz frequency that can be received with cheap RF 433MHzreceiver and then decoded in to real data that can be further used in your own project. Using Raspberry Pi it becomes easy to write a simple script that would log soil moisture data in to database that could be access via web interface. It could send email or other type of alerts when plant needs attention. Another benefit that Ray points out is that cheap wireless sensor already comes in nice water proof enclosure, battery and sensor itself. Great source for home automation projects.