Poking a finger into the soil works until you go away for a week, or until you have more beds than you can check in a day. A soil moisture sensor does the poking for you. With the right setup you can read it from anywhere, and see how fast the soil dries out between waterings.

The three pieces

Every remote soil monitor, whatever the brand, is made of the same three parts.

  1. A sensor in the soil. It measures how wet the soil is around its probe.
  2. A way to get the reading online. Some sensors send by radio to a small gateway plugged into your Wi-Fi. Others are a Wi-Fi board with a probe attached.
  3. A place to look at the numbers. A dashboard that keeps your history and draws a chart.

The sensor and the connection usually come together in one product, so the real choice is between a ready-made kit and a build-it-yourself board.

Ready-made kit or DIY board

A ready-made kit is the easy route. Ecowitt, for example, sells a battery-powered soil sensor that talks by radio to one of its gateways, and the gateway sends the readings over your home Wi-Fi. You pair the sensor once and then forget about it, apart from changing the battery. Our Ecowitt page shows how to send those readings to SensorConsole.

A DIY board costs less and gives you more control. An ESP32 with a capacitive soil probe is a few dollars of parts, and you decide how often it reports. It does need a little code. If you want to go that way, start with the guide on choosing a soil moisture sensor for Arduino, then follow sending ESP32 data to a website.

Where to put the probe

Placement matters more than the price of the sensor.

  • Put the probe at root depth. For vegetables and flowers that is usually 10 to 15 cm (4 to 6 inches). For a houseplant, about halfway down the pot.
  • Keep it away from the drip emitter. Right under the emitter the soil is always wet and tells you nothing about the rest of the bed.
  • Push it in firmly. An air gap along the probe gives a falsely dry reading. Water the soil lightly after inserting so it settles around the blade.
  • Use one sensor per growing zone. A bed in full sun and a bed in shade dry out at different speeds, so one sensor cannot speak for both.
  • Keep the electronics dry. Most capacitive probes are only waterproof up to a marked line. Do not bury the part with the chip on it.

What the number means

A soil moisture percentage is not a universal measurement. It is a position between two points that were set when the sensor was calibrated, usually 0 for dry air and 100 for sitting in water. Sandy soil and clay soil read differently at the same real wetness, and two sensors of the same model can differ a little.

So do not trust a number from a chart in a gardening book. Learn your own. Water a bed until you are happy with it and note the reading. Wait until the plants start to look thirsty and note it again. Those two values become your own rules, something like "water below 30" for that bed.

You can have SensorConsole watch for that for you. On the device page, open the Alerts box under Threshold alerts, choose your soil reading, choose goes below and type your number. When a reading crosses it, you get an email. Each alert sends at most one email every six hours, so a dry spell does not flood your inbox.

Setting it up on SensorConsole

  1. Create a free account and sign in.
  2. Choose Connect a sensor, give it a name such as "Tomato bed", and set the category to Soil moisture.
  3. Pick how it connects. A Wi-Fi station with a custom server option uses Custom server push. A board you programmed yourself uses Generic/DIY push.
  4. Copy the details shown on the device page into your gateway app or your code.
  5. Wait a few minutes. The first reading shows up on the device page, and the history chart starts to fill in.
  6. Once you know your dry value, add a threshold alert in the Alerts box so you hear about it without checking.

Your history is kept for as long as your account exists, so next summer you can compare it with this one.

Reading the chart

A healthy bed draws a sawtooth. The line climbs when you water or it rains, then slopes down as the soil dries. Three patterns are worth knowing.

  • A steep rise followed by a slow fall is normal watering. The slope of the fall tells you how fast that bed dries, which is the number you need to schedule watering.
  • A line stuck at 0 or at 100 for days is usually a sensor problem, such as a dead battery, a loose wire or a probe that has lost contact with the soil.
  • A slow drift upward with no watering can mean a leak in an irrigation line near the probe.

Use the 24 hour view to see the daily rhythm, and the 30 day or 1 year view to see how the seasons change your watering needs. In the long views each day shows its average, lowest and highest value.

Mistakes that waste a season

  • Buying a resistive probe with two bare metal prongs. They corrode in wet soil within weeks and their readings drift. Choose a capacitive probe with a coated board.
  • Placing the probe in a spot that is not typical of the bed, such as next to a path or right by the stem.
  • Treating one reading as the truth. Look at the trend over a day or two before reacting.
  • Forgetting the battery. If a sensor goes quiet, check this list before replacing anything.