There’s a certain kind of person who looks at their garden irrigation timer and thinks, “Yeah, but what if my garden could check the weather forecast, read the soil moisture, and decide for itself whether to water?” If that sounds like you, welcome to the rabbit hole. Home Assistant garden automation is where smart home tech meets practical horticulture, and once you start, you won’t look at a dumb timer the same way again.

This guide walks you through the practical setup — from getting Home Assistant running, to building DIY soil moisture sensors with ESPHome, to creating automations that actually save water and grow better plants. It’s written for people who want results, not people who want to tinker endlessly (though if you’re the tinkering type, there’s plenty here for you too).

Why Home Assistant for Garden Automation?

You might be wondering why you need a whole home automation platform just to water plants. Fair question. Here’s why Home Assistant beats dedicated smart irrigation controllers:

It Connects Everything

Dedicated irrigation controllers (Hunter Hydrawise, Orbit B-Hyve, Rachio) do one thing — control zones on a schedule, maybe with a weather adjustment. Home Assistant connects your irrigation to everything else: soil moisture sensors, rain sensors, weather forecasts, temperature readings, tank water levels, even your home’s energy system (water during off-peak solar hours, anyone?).

It’s Local

No cloud dependency. Your garden automations run on a little box in your house, not on some company’s server that might go down, get hacked, or shut down their API when they pivot to a different business model. When Insteon died, their users lost everything. Your Home Assistant will still be watering your tomatoes.

It’s Free (Software-wise)

Home Assistant is open-source. Free forever. The hardware to run it costs $50-200 depending on what you use, but there are no subscriptions, no premium tiers, no “pay $5/month to unlock advanced scheduling.”

It’s Ridiculously Flexible

Want to water Zone 3 only when soil moisture drops below 40%, it hasn’t rained in the last 24 hours, the forecast shows no rain in the next 12 hours, and it’s not currently above 38°C? That’s about 10 lines of automation config. Try doing that with a $50 irrigation timer.

Getting Started: What You Need

The Home Assistant Hub

You need something to run Home Assistant on. Options from simplest to most flexible:

Home Assistant Green (~$150 AUD)

Raspberry Pi 4/5 ($80-$130 AUD + SD card/SSD)

Old PC or Intel NUC ($0-$200)

Virtual Machine

Irrigation Control Hardware

You need a way for Home Assistant to actually turn water on and off. Several approaches:

Smart Solenoid Valves (WiFi/Zigbee)

Smart Relay Controlling Existing Solenoids

All-in-One Smart Irrigation Controllers

DIY ESP32 + Relay Board

Soil Moisture Sensors

This is where garden automation gets genuinely smart. Instead of watering on a schedule, you water based on what the soil actually needs.

Capacitive Soil Moisture Sensors + ESPHome (DIY)

Xiaomi/Miflora Plant Sensors

Ecowitt Soil Moisture Sensors

Building DIY Soil Moisture Sensors with ESPHome

ESPHome is a firmware framework for ESP32/ESP8266 microcontrollers that integrates natively with Home Assistant. If you’re new to it — don’t panic. It’s way easier than it sounds.

What You Need (Per Sensor Node)

Total cost per sensor node: $20-40 (can monitor 1-4 zones per node)

ESPHome Configuration

Here’s a basic ESPHome config for a soil moisture sensor:

esphome:
  name: garden-moisture-01
  platform: ESP32
  board: esp32dev

wifi:
  ssid: "YourWiFiName"
  password: "YourWiFiPassword"

api:
  encryption:
    key: "your-generated-api-key"

ota:
  platform: esphome
  password: "your-ota-password"

sensor:
  - platform: adc
    pin: GPIO34
    name: "Veggie Bed Soil Moisture"
    update_interval: 300s
    unit_of_measurement: "%"
    attenuation: 11db
    filters:
      - calibrate_linear:
          - 2.85 -> 0.0    # Sensor in dry air
          - 1.28 -> 100.0  # Sensor in water
      - lambda: |-
          if (x < 0) return 0.0;
          if (x > 100) return 100.0;
          return x;

Calibrating Your Sensors

The calibrate_linear values above are examples. You need to calibrate each sensor:

  1. Dry reading: Hold the sensor in dry air and note the raw ADC value (shown in HA logs)
  2. Wet reading: Submerge the sensor in a glass of water and note the value
  3. Update your config with these two reference points

Capacitive sensors aren’t laboratory instruments, but they’re accurate enough to tell you “dry,” “moist,” or “wet” — which is all you need for irrigation decisions.

Weatherproofing

Your ESP32 and connections need to survive outdoors. Here’s what works:

Weather Integration

Home Assistant can pull weather data from multiple sources and use it in your garden automations:

Bureau of Meteorology (BoM)

The bom integration gives you current conditions and forecasts from your nearest BoM weather station. This is Australian-specific data, which is far more useful than global weather services for local garden decisions.

Install via HACS (Home Assistant Community Store) — search for “Bureau of Meteorology.”

OpenWeatherMap

Free tier gives you current weather, 5-day forecast, and rain probability. Good supplement to BoM data.

Personal Weather Stations

If you have an Ecowitt, Ambient Weather, or Davis weather station, integrate it directly. Local microclimate data from your actual property is always better than data from the nearest BoM station 20km away.

Weather Data You Want for Garden Automation

Building Your Dashboard

A good garden automation dashboard gives you at-a-glance status without needing to dig through menus. Here’s a practical layout:

Section 1: Current Conditions

Section 2: Controls

Section 3: History

Example Dashboard Card (YAML)

type: gauge
entity: sensor.veggie_bed_soil_moisture
name: Veggie Bed
min: 0
max: 100
severity:
  green: 40
  yellow: 25
  red: 0

Example Automations

Here’s where the magic happens. These are real automations you can adapt:

Automation 1: Water When Dry (Basic)

alias: "Water veggie bed when dry"
trigger:
  - platform: numeric_state
    entity_id: sensor.veggie_bed_soil_moisture
    below: 35
    for:
      minutes: 30
condition:
  - condition: time
    after: "06:00:00"
    before: "09:00:00"
  - condition: state
    entity_id: input_boolean.irrigation_enabled
    state: "on"
action:
  - service: switch.turn_on
    target:
      entity_id: switch.irrigation_zone_1
  - delay:
      minutes: 15
  - service: switch.turn_off
    target:
      entity_id: switch.irrigation_zone_1

This waters Zone 1 for 15 minutes when soil moisture drops below 35%, but only during the morning window and only if irrigation is globally enabled.

Automation 2: Skip Watering if Rain Expected

alias: "Cancel watering if rain forecast"
trigger:
  - platform: time
    at: "05:30:00"
condition:
  - condition: numeric_state
    entity_id: sensor.bom_rain_chance_today
    above: 70
  - condition: numeric_state
    entity_id: sensor.bom_rain_amount_forecast
    above: 5
action:
  - service: input_boolean.turn_off
    target:
      entity_id: input_boolean.irrigation_enabled
  - service: notify.mobile_app
    data:
      message: "Irrigation skipped — BoM forecasts >5mm rain today ({{ states('sensor.bom_rain_chance_today') }}% chance)"

At 5:30am each day, this checks the BoM forecast. If there’s more than a 70% chance of at least 5mm of rain, it disables irrigation for the day and sends you a notification.

Automation 3: Heatwave Protection

alias: "Extra watering on extreme heat days"
trigger:
  - platform: numeric_state
    entity_id: sensor.outside_temperature
    above: 40
condition:
  - condition: time
    after: "05:00:00"
    before: "07:00:00"
action:
  - service: switch.turn_on
    target:
      entity_id: switch.irrigation_zone_all
  - delay:
      minutes: 20
  - service: switch.turn_off
    target:
      entity_id: switch.irrigation_zone_all
  - service: notify.mobile_app
    data:
      message: "🔥 Heatwave watering triggered — all zones for 20min ({{ states('sensor.outside_temperature') }}°C)"

When the temperature hits 40°C during early morning hours, hit everything with a good soak. Your plants will thank you.

Automation 4: Tank Water Level Warning

If you’re irrigating from a rainwater tank (common in Australian garden setups):

alias: "Tank low water warning"
trigger:
  - platform: numeric_state
    entity_id: sensor.water_tank_level
    below: 20
action:
  - service: notify.mobile_app
    data:
      message: "⚠️ Water tank is at {{ states('sensor.water_tank_level') }}%. Consider switching to mains or reducing irrigation."
  - service: input_number.set_value
    target:
      entity_id: input_number.irrigation_duration_multiplier
    data:
      value: 0.5

When the tank drops below 20%, it alerts you and automatically halves all irrigation durations. Smart water management without lifting a finger.

The Learning Curve: Being Honest

Let’s not pretend this is plug-and-play. Home Assistant garden automation has a learning curve:

Easy (Week 1):

Medium (Week 2-4):

Advanced (Month 2+):

You don’t need to do it all at once. Start with one zone, one sensor, one automation. Get that working reliably, then expand.

What It Costs: The Full Breakdown

ComponentCost (AUD)
Home Assistant hardware (HA Green or RPi)$80-$150
ESP32 board + capacitive sensor (1 zone)$15-25
Smart relay for solenoid (1 zone)$15-30
Waterproof enclosure + sundries$10-20
Total for 1-zone starter setup$120-$225
Each additional zone (sensor + relay)$25-50
Full 4-zone setup$200-$375

Compare that to a Hydrawise 6-zone controller at $350+ (without soil moisture sensors), and the DIY route is competitive on price while being infinitely more flexible.

Tips From the Trenches

Start simple. Your first automation should be basic. Get reliable before getting clever.

Use input_boolean toggles. Always have a global “irrigation enabled” toggle. When something goes wrong (and it will, at first), you want a single switch to turn everything off.

Monitor before automating. Run your soil moisture sensors for 2-3 weeks before creating automations. Understand what “normal” looks like for your garden — different beds, different soil, different sun exposure will all read differently.

Waterproof everything twice. Australian conditions are harsh. Heat, UV, rain, and possums will all test your installations. Over-engineer the weatherproofing.

Keep a manual backup. Your irrigation system should still work manually if Home Assistant goes down. A physical valve or tap bypass is essential.

Log everything. Home Assistant’s recorder and history components let you track soil moisture, watering events, and weather data over time. This data is gold for understanding your garden’s needs across seasons.

Going Further

This guide gets you from zero to a functional automated garden. But there’s a lot more you can do — drip irrigation optimisation, building wicking bed auto-fill systems, integrating with rainwater harvesting, and using machine learning to predict your garden’s water needs.

Set and Forget: The Aussie Guide to Automated Gardening covers the complete system, from sensor selection through to advanced automations that handle an entire food production garden with minimal human intervention. If you’ve got the Home Assistant bug and a garden that needs looking after, it’s the logical next step.

Now go build something. Your tomatoes are waiting.

📚
Want the full picture? This post is a taste of what's in Set and Forget: The Aussie Guide to Automated Gardening. The book goes deeper — with more data, more strategies, and zero filler.
See the full book →

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