Keeping track of how much you need to water your plants can be a very simple and low tech process, but sometimes it's good to bring some technology into the mix for making sure you're not using too much water, taking care of a more delicate plant or just gathering some hard data to back up your plant care. And let's not forget, this project let's you use everybody's favorite DIY gadget, the Raspberry Pi.
This project comes from Instructables user JenFoxBot who says, "Agriculture consumes between 80 - 90% of all freshwater in the United States. An easy way to conserve water in the agricultural sector is to install a soil moisture sensor. Soil moisture sensors measure the amount of water in the soil to maintain consistent and ideal soil conditions for plants. In some cases, installing a soil moisture sensor reduces residential irrigation by as much as 50%.
The following is a simple capacitive soil moisture sensor using a Raspberry Pi and a co-planar capacitor from the Zero Characters Left blog.
Excluding the Pi, the system can be built for less than $25.
You can also power the system using a portable solar USB charger and install it outdoors! Yay :)"