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Water the garden on a schedule

Water the garden on a schedule

How it works

A garden irrigation valve opens when 24 V AC reaches its solenoid. A Shelly 1 Gen4 puts a dry contact in that circuit, so the valve keeps its own plug-pack and the relay only decides when the circuit closes.

Clip a Shelly Plus Add-on onto the relay and it can read an analogue soil moisture sensor. The Shelly checks the reading every minute and, when the soil drops below the level you set, runs the valve for a set time. A timer on the relay keeps it from running on if anything goes wrong.

  1. Shelly app main screen for a device named Front yard sprinkler, showing soil moisture at 30% and a Turn on button. 01

    Your phone

    Check the soil reading, or skip a run when rain is coming.

  2. 1 Gen4 Smart Relay 02

    Shelly relay

    Opens the valve when the soil is dry, for a set time.

  3. 03

    Your garden

    Gets watered when it needs it, not on a fixed clock.

What it looks like on your phone

  • Check the soil from anywhere. The main screen shows the moisture reading beside the Turn on button.

  • Water now. Tap Turn on and it runs until auto off stops it at 30 minutes, or tap again to stop it sooner.

  • Pause it for a wet week. The switch beside Water when dry turns the rule off; turn it back on when the rain stops.

  • See every run. The activity log lists each time the sprinkler turned on and off.

Step by step

How you'll set it up

Add the device to Wi-Fi from your phone, or straight from a browser.

Download Shelly Smart Control on the App Store Get Shelly Smart Control on Google Play

  1. Fit the Shelly beside the irrigation plug-pack

    One plug-pack lead lands on I, O runs to the valve, and the valve's other wire goes back to the plug-pack's common. L and N power the relay itself.

    Wire map 1 Gen4
    • Active (supply) L
    • Neutral N
    • 24 V AC plug-pack I
    • Valve O
    Circuit overview
    LN230 V~ 50 Hz24 V valveOISWLNShelly 1 Gen4
    Active (supply)Neutral / 0 VSwitch signal / dry contact

    In Australia, fixed 230 V wiring is licensed-electrician work. Use these diagrams to plan the job and brief your electrician.

    Showing the whole circuit

    Shelly 1 Gen4

    100%
    LN230 V~ 50 Hz24 V valveOISWLNShelly 1 Gen4

    Select a terminal to follow its wiring.

  2. Wire the soil sensor to the Add-on

    With the power off, clip the Shelly Plus Add-on onto the relay. On the SMT50, the brown wire goes to VCC, white to GND and yellow to ANALOG IN. The green wire is the temperature output; leave it unconnected. Push the probe into the bed at root depth.

    Wire map Plus Add-on
    • Brown (power) VCC
    • White (ground) GND
    • Yellow (moisture) ANALOG IN
    Circuit overview
    3.3 V from the ShellyGreen: not connectedSoil sensor1-Wire sideAnalogue sideShelly Plus Add-onVCCGNDANALOG IN
    Brown: power (VCC)White: ground (GND)Yellow: moisture (ANALOG IN)Green: temperature, not connected

    In Australia, fixed 230 V wiring is licensed-electrician work. Use these diagrams to plan the job and brief your electrician.

    Showing the whole circuit

    Shelly Plus Add-on

    100%
    3.3 V from the ShellyGreen: not connectedSoil sensor1-Wire sideAnalogue sideShelly Plus Add-onVCCGNDANALOG IN

    Select a terminal to follow its wiring.

  3. Add the Shelly in the app

    Add the relay in the Shelly Smart Control app and name it Front yard sprinkler.

    Learn how to add a device to the Shelly app

  4. Turn on the Sensor Add-on

    Open Add-on peripherals, expand Manage add-on feature, choose Sensor Add-on, then tap Save and reboot. In the web interface, open Add-on, choose Sensor Add-on and click Save and reboot.

  5. Add the sensor as a Voltmeter

    Tap Add peripheral, choose Voltmeter and tap Add peripheral. The Shelly asks to reboot once more. In the web interface, click +, choose Voltmeter and click Add and reboot.

  6. Show the reading as moisture

    Open the peripheral's settings and name it Soil moisture. Set the custom expression to x*50/3 and the unit to %, then tap Save. In the web interface, open Soil moisture, enter the same expression and unit and click Save. The SMT50 puts out 0 to 3 V for 0 to 50% moisture, so the app now shows a percentage instead of volts.

  7. Check the reading

    Soil moisture now shows on the device's main screen. Damp potting mix read about 30% on our bench, and dry soil drops towards single figures.

  8. Water when it's dry

    Under Actions, add an action named Water when dry. Trigger it on the measurement every 60 seconds, add the condition Transformed voltage value less than 20, and set the action to turn Front yard sprinkler on and flip it back after 600 seconds. Set Repeat when to 3600, so it waters at most once an hour and the water has time to soak in. To water only in the early hours, set Active time from 02:00 to 03:00: with Repeat when at 3600, that's one run a night at most.

  9. Add a backstop

    Open Timer, turn on Auto off at 30 minutes and tap Save. In the web interface, tick Enable under Auto OFF, set the delay to 1800 seconds and click Save. If the sensor ever stops reporting, the valve still can't run all day.

  10. Check it's set

    Add-on peripherals now shows Soil moisture with its reading and, under Actions, Water when dry: below 20%, between 02:00 and 03:00. The valve opens the next time the soil dries out in that window.

Frequently asked questions

Should I use the Shelly app or Home Assistant?

If you don't run Home Assistant, use the Shelly app: it needs no hub, and the watering rule runs on the relay, so it keeps working when the internet is down. If Home Assistant already runs your home, put the garden there, so the watering can sit alongside your other automations.

Will it water when it's already raining?

Not if the soil is wet. The rule only runs the valve when the sensor reads below your dry point, so a wet bed stays off.

Which soil moisture sensor should I use?

We tested the Truebner SMT50, a buried analogue probe with a 10 m cable. The Add-on reads any sensor with a 0 to 10 V output; you'd change the expression and the dry point to suit its range.

What dry point should I set?

Start at 20% and watch a week of readings. If the bed looks thirsty before it waters, raise it; if it stays soggy, lower it.

Can I water on a timer instead?

Yes. Leave out the condition, so the automation runs the valve at 2 am every night, or add a Time condition that ticks only the days you want.

Can it skip watering when rain is forecast?

Yes, with Shelly Premium, the paid tier of the Shelly app. A scene can check the forecast for the next one to six hours and only turn the sprinkler on when the chance of rain is below a level you choose. Scenes run in Shelly's cloud, so they need an internet connection; the Water when dry rule above runs on the relay itself.

How many zones can one Shelly run?

One valve per Shelly 1 Gen4. For more zones, fit one relay per valve; each can have its own Add-on and sensor, or share one sensor's reading through a scene.

Does it still water if Home Assistant is off?

No. The automation runs in Home Assistant, so nothing waters while it's down, and the Auto off timer on the relay still stops any run that's under way. If you'd rather the rule ran on the relay itself, set it up in the Shelly app instead.

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