How to Make Your Own Soil Moisture Sensor

What You'll Need
Analogue measuring device
2 Metal pieces (nails, wall hangers)
Plaster of Paris
Plastic tube or wide straw
Mixing bowl
Glue gun
Pair of gloves

A soil moisture sensor is used to measure the moisture content of the soil, which helps in regulating the watering cycles for optimal plant growth. You can make your own soil moisture sensor at home which is an economical alternative to the similar gadgets available in the market. The sensor is made using metal probes which are inserted into a block of gypsum; the resistance between them gives you the moisture levels which are read using an analogue measuring device. The steps below guide you through a simple easy to do process of how to make your own soil moisture sensor:

Step 1 – Setting the Metal Pieces

If you are using metal wall hangers straighten them out (you can use nails which are easier to use, make sure they are 1 1/2 inches in length) set them about 15 millimeters apart. Insert them into the straw which is cut to about 4 inches in length. Put glue on the top end to hold them in place. Make sure a part of the nails protrude beyond the straw.

Step 2 – Mixing Plaster of Paris and Making the Mould

The ideal material for moisture sensors is gypsum, but Plaster of Paris works just as well as it is gypsum heated at very high temperatures. Mix the plaster according to the directions given on the label; use a small skewer or screwdriver to insert the Plaster of Paris into the straw. Gently tap the straw to settle the Plaster of Paris and remove air bubbles. When you reach the top use the edge of the screwdriver to form a sort of conical shape; set the probe aside in an upright position to let dry. You can tape the probe against a flat wall to hold it in position.

Step 3 – Preparing the Probe

Dry the probe for 24 hours before you proceed to the next step. Cut away part of the straw to reveal the dried Plaster of Paris, you can use a cutter to do this. Now your moisture sensor is ready to be tested.

Step 4 – Testing the Device

To test the moisture sensor hook up the cables of the analogue measuring device to the protruding nails. This will give you a reading which will be the standard reading of the device when dry; you can use these to gauge the moisture content of the soil by comparing the readings.

Step 5 – Tips and Advice

Wear protective gloves to protect your hands from any chemicals (such as Plaster of Paris), that may act as irritants. If you have metal hangers they are a better alternative to nails. One pack of Plaster of Paris can give you plenty of moisture sensors and they work well in grow boxes as well. Insert the moisture sensor into the soil so as to immerse leave the top of the sensor above the soil for accurate readings.