Use Soil Moisture to Control a Light in Home Assistant (Veggie Hub + VH400)

The Simple Idea: Plants Communicate With Light

Here’s the demo: a light is tied to a plant’s soil moisture level. When the soil dries out past a threshold, Home Assistant turns the light ON. After watering, the moisture rises and the light turns OFF. It’s an easy, obvious “status indicator” you can see from across the room.

Hardware Used

• VegeHub Wi-Fi Data Logger — connects to your local Wi-Fi and exposes sensor readings to Home Assistant.
• VH400 Soil Moisture Sensor — outputs a voltage that correlates to volumetric water content.

Together, the Veggie Hub + VH400 provide live soil moisture data that Home Assistant can display, graph, and automate.

Home Assistant Setup: Device Discovery

The Veggie Hub is fully supported in Home Assistant. Once you connect it to your local Wi-Fi, it should automatically appear in Home Assistant as a discovered device. From there you can add it and start seeing sensor readings immediately.

Convert Raw Voltage to Soil Moisture With a Template Sensor

The Veggie Hub reports the raw sensor voltage. To turn that into a meaningful “soil moisture” value, create a template sensor in Home Assistant that converts voltage into soil moisture.

Once you have a soil moisture entity, you can:

• Put it on a dashboard
• Graph it over time
• Use it in automations
• Trigger alerts or notifications
• Control valves, switches, lights, fans—anything Home Assistant can control

Create an Automation: Dry Turns Light On, Wet Turns Light Off

A simple automation watches your soil moisture level and uses two thresholds:

• Below a “dry” value → turn the light ON
• Above a “wet” value → turn the light OFF

Using two thresholds (instead of one) prevents the light from flickering if the reading hovers near a boundary.

What You Can Do Next

Once soil moisture is in Home Assistant, the fun part begins. You can build automations like:

• Turn on a pump or solenoid valve for automated watering
• Send an alert when a plant is trending dry
• Trigger a “check plants” reminder only when it’s actually needed
• Combine moisture + time + temperature for smarter irrigation logic
• Log moisture history to compare soil mixes, pot sizes, and watering habits

The point is simple: once you have the data, Home Assistant can do whatever you want with it.

Configs and Exact Examples

In the video description I’ll link the exact configurations I use, including:

• Template sensor examples (voltage → soil moisture)
• Notes on connecting devices to Home Assistant
• Automation examples for lights, alerts, and more

Copy the configs, adjust the thresholds for your plant, and you’ll have a reliable “plant status light” in minutes.