Take your gardening project to the next level with a SHT-10 based soil sensor. The sensor includes a temperature/humidity sensor module from Sensiron in a sinter metal mesh encasing. The casing is weatherproof and will keep water from seeping into the body of the sensor and damaging it, but allows air to pass through so that it can measure the humidity (moisture) of the soil. It is designed to be submersible in water, but it's always best to avoid long-term (over 1 hour at a time) submersion, if you need something that can be submerged for over an hour you may want to find a different sensor. It can also be simply placed outside for exterior weather sensing.
Humidity readings have 4.5% precision, temperature is 0.5% precision. A microcontroller is required to interface. The sensor is not washed after reflow and is rehydrated according to datasheet requirements.
The sensor is essentially just a Sensiron SHT-10 with the 4 data/power wires brought out so any SHT-1X code for a microcontroller will work. The sensor works with 3 or 5V logic. The 1 meter long cable has four wires: Red = VCC (3-5VDC), Black or Green = Ground, Yellow = Clock, Blue = Data. For Arduino, there's a handy Sensiron library with example. For Propeller, there's an SHT1X sensor object. Don't forget to connect a 10K resistor from the blue Data line to VCC.
Soil Temperature/Moisture Sensor (8:52)