Tools like tensiometers should be removed from the ground each year and soaked in vinegar or a weak acid. Acid should also be put inside the instrument and left to.soak overnight. Gauges should be checked and unit should be checked for leaks. Gauges can freeze if left out over the winter and can crack, or break.
Tensiometers should be reinstalled back into the soil at the correct depth. The tube needs a good soil connection, this is best done by pouring a slurry of mud down the hole where you installed the meter, leaving a few inches above the neck from the soil. The gauge should be off the ground. The instrument should be refilled with green dyed water, this will keep algae from growing in the reservoir. A vacuum pump should be applied to bring the pressure up to about 80 psi. If the pressure holds steady it is working correctly, if pressures drop there is a problem with the soil connection or the instrument. The reservoir should then be refilled and cap put on tightly.
Watch the pressure begin to rise on the gauge over the next few minutes. This will indicate it is working correctly.
Watermark sensors are much more free of maintenance and give similar readings, they can be left in the soil 3 to 5 years providing maintenance free soil moisture readings for years, they are less expensive than tensiometers, and more durable. They are easier to hook up to data loggers if you want more information. Unless you have several watermarks the automated reader is a little expensive. However if you use more than few it is well worth the cost.