Soil Moisture Sensors

What does a soil moisture sensor measure?

Sensors estimate how much water is in the soil, using electrical properties or the tension that plants must overcome to take water up. Some give a number, some give a color or a simple wet-or-dry signal. Different types suit different jobs, from a garden bed to a pivot-irrigated field.

Readings are estimates. Their meaning depends on soil type, so a number that signals dry in sand may signal fine in clay. Do not treat a single sensor as the whole field. Fields vary with slope, soil and past management, and one spot can mislead you in both directions.

• Estimates water in the root zone
• Readings vary by soil type
• Different designs suit different uses

Where do I place sensors?

Place them where plants really take up water, at depths that match the root zone, and in spots that represent the field. Avoid the wettest corner, the driest knoll, compacted tracks and spots near a dripper or sprinkler head unless that is what you want to measure. Using more than one depth shows how water moves down.

Install carefully, so the sensor makes full contact with soil and there are no air gaps. Poor contact gives poor readings.

Mark the spot so tillage, mowing and tractors miss it. Call your state one-call service before digging near buried lines. Ask your NRCS or extension office what soil types you have, since a soil map can tell you whether your sensor sits in a sandy knoll or a heavy low spot.

How do I read and use the numbers?

Learn what is normal for your soil by watching readings after a rain and after a dry spell. Over a season you learn what wet, comfortable and dry look like at your site. Note readings alongside what you see in plants and what you feel when you dig.

Use sensors to guide decisions, not to make them alone. Check the soil by hand, look at the crop and consult local guidance on how much water your crop needs and when. Dig a small pit next to the sensor when you install it, and look at the layers. Roots, rocks and a hard layer below can change how water moves and where the sensor should sit.

What are the limits?

Sensors can drift, fail or be affected by salt, rocks, roots and air pockets. They measure one small spot, and a field can vary a lot. A sensor may also read unusually after freezing or in very dry cracking soil. Compare with a hand check regularly.

Power and signal may limit remote reading. Some sensors store data until you collect it, and some need a connection. Plan battery changes and consider what you will do if the system fails. Keep a short note of each reading with the date, weather and what you did, such as irrigated or skipped. After a year you can see what each reading meant for your crop.

How can sensors save water and money?

The main benefit is avoiding watering too much or too little. Too much water wastes money and energy, leaches nutrients and invites disease. Too little stresses plants. Sensors help you find the middle, and records show whether a change in practice made a difference.

Check local water rules, since irrigation limits and permits vary. Your conservation district, NRCS office or extension office can explain programs that may help with irrigation efficiency, and what is available in your area.

Drought.gov shows current conditions in your region, which can help you decide how to plan. Learn the difference between water the soil holds and water plants can use. Heavy soils hold more water that plants may struggle to extract, while sandy soils drain fast.

How do I start small?

Place a few sensors in a garden or one field and compare them to your hand checks for a season. Keep notes. Learn which readings match your experience. Add more only when you know what you want to learn. Local extension programs often hold workshops on irrigation scheduling and may have loaner sensors.

A simple probe or the old method of digging a hole and squeezing a handful of soil remains valuable even when you have sensors. Think about your crop. Shallow-rooted vegetables, deep-rooted pasture and tree fruit all need different depths and different attention, and a local specialist can guide you.

Last reviewed: November 12, 2026. Written by the Rural Farm Life Editorial Team. See our editorial policy.