SHT-10 based Soil Moisture & Temperature 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. For Arduino, there’s a handy Sensiron library with an example.

Features:

Relative Humidity and Temperature Measurement
Excellent Long Term Stability
Waterproof Package, and Can be Used for Measurement of Soil
Low Energy Consumption

Specifications:

Temperature Reading Accuracy (°C)	0.5
Humidity Reading Accuracy (%)	4.5
Cable Length (Meter)	1
Operating Temperature (°C)	-40 to120
Humidity Measurement Range (%RH)	0 to 100
Length (mm)	50
Diameter (mm)	14
Weight (gm)	20