Smart Garden Irrigation System - Complete DIY Guide

Automatic irrigation saves water, time and ensures healthy plants even during vacation. In this detailed guide, I'll show you how to build a smart irrigation system that responds to weather, soil moisture and can be controlled from anywhere.

Why Smart Irrigation?

Traditional irrigation systems run on timers regardless of actual need. A smart system:

• Measures soil moisture - waters only when needed
• Monitors weather - skips irrigation before rain
• Different zones - each garden area according to need
• Remote control - monitoring from anywhere
• Statistics - track water consumption

System Components

Basic Hardware

1. Control Unit

• ESP32/ESP8266 ($8-16) - WiFi microcontroller
• Raspberry Pi ($60-100) - more advanced option
• Arduino + WiFi shield ($32-48) - classic choice

2. Valves and Piping

Solenoid valves:
- 24V AC valves ($32-60/piece)
- 12V DC valves ($24-40/piece)
- Diameter by flow rate (3/4" or 1")

Piping:
- PE hose 16-25mm
- Connectors, elbows, T-joints
- Drippers or sprinklers

3. Power Supply

• 24V AC transformer ($20-32)
• Or 12V DC supply + relay board

4. Sensors

• Soil moisture ($6-12/piece)
• Rain sensor ($8-16)
• Water flow ($20-40)
• Temperature/humidity ($8-16)

Example Budget

Small garden (4 zones):

ESP32: $12
4x 12V valve: $96
8-channel relay module: $8
4x moisture sensor: $32
Power supply: $16
Box, cables: $20
Piping and fittings: $60
Total: ~$244

Medium garden (8 zones):

Raspberry Pi: $80
8x 24V valve: $320
Expander + relays: $32
8x sensors: $64
24V transformer: $32
Flow meter: $32
Installation materials: $80
Total: ~$640

System Planning

1. Zone Division

By plant type:

• Zone 1: Lawn (daily short)
• Zone 2: Flower beds (2-3x weekly longer)
• Zone 3: Shrubs (1x weekly heavy)
• Zone 4: Greenhouse (frequent light)

By sun exposure:

• South side - more frequent watering
• North/shade - less frequent

2. Flow Calculation

Example calculation:
- Water pressure: 3 bars
- Faucet flow: 15 l/min
- Sprinkler: 2 l/min
- Max sprinklers/zone: 7

Drippers:
- Dripper: 2-4 l/hour
- Per zone: up to 50 drippers

3. Water Distribution

Main supply piping:

• PE 25-32mm or 1"
• Bury 30-40cm (frost protection)
• Slope for drainage

Distribution to plants:

• PE 16-20mm
• Or micro tubing 4-6mm
• Stake anchoring

Electronics Assembly

ESP32 Solution (Recommended)

Required Components:

- ESP32 DevKit
- 8-channel 5V relay
- 5V/3A power supply
- Terminal blocks
- IP65 enclosure
- Connection cables

Wiring:

ESP32 -> Relay module:
GPIO23 -> IN1 (Zone 1)
GPIO22 -> IN2 (Zone 2)
GPIO21 -> IN3 (Zone 3)
GPIO19 -> IN4 (Zone 4)
VIN -> VCC
GND -> GND

Moisture sensors:
GPIO34 -> Sensor 1 (analog)
GPIO35 -> Sensor 2 (analog)
GPIO32 -> Sensor 3 (analog)
GPIO33 -> Sensor 4 (analog)

Valves:
Relay NO -> Valve (+)
12V supply -> Valve (-)

ESP32 Code

#include <WiFi.h>
#include <WebServer.h>
#include <ArduinoJson.h>

// WiFi credentials
const char* ssid = "YourWiFi";
const char* password = "YourPassword";

// Pins
const int zone_pins[] = {23, 22, 21, 19};
const int moisture_pins[] = {34, 35, 32, 33};
const int num_zones = 4;

// Settings
int moisture_threshold[] = {30, 40, 35, 45}; // %
int watering_duration[] = {300, 600, 900, 300}; // seconds

WebServer server(80);

void setup() {
  Serial.begin(115200);
  
  // Setup pins
  for (int i = 0; i < num_zones; i++) {
    pinMode(zone_pins[i], OUTPUT);
    digitalWrite(zone_pins[i], LOW);
  }
  
  // WiFi connection
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.println("Connecting to WiFi...");
  }
  
  Serial.println("Connected! IP: " + WiFi.localIP().toString());
  
  // Web server endpoints
  server.on("/", handleRoot);
  server.on("/status", handleStatus);
  server.on("/water", handleWater);
  server.on("/settings", handleSettings);
  
  server.begin();
}

void loop() {
  server.handleClient();
  
  // Check moisture every 30 minutes
  static unsigned long lastCheck = 0;
  if (millis() - lastCheck > 1800000) { // 30 min
    checkMoistureAndWater();
    lastCheck = millis();
  }
}

void checkMoistureAndWater() {
  for (int i = 0; i < num_zones; i++) {
    int moisture = readMoisture(i);
    
    if (moisture < moisture_threshold[i]) {
      Serial.println("Zone " + String(i+1) + " dry (" + 
                     String(moisture) + "%) - watering");
      waterZone(i, watering_duration[i]);
    }
  }
}

int readMoisture(int zone) {
  int raw = analogRead(moisture_pins[zone]);
  // Convert to percentage (calibrate per sensor)
  // Dry = 4095, Wet = 1000
  int percent = map(raw, 4095, 1000, 0, 100);
  return constrain(percent, 0, 100);
}

void waterZone(int zone, int duration) {
  digitalWrite(zone_pins[zone], HIGH);
  delay(duration * 1000);
  digitalWrite(zone_pins[zone], LOW);
}

void handleRoot() {
  String html = R"(
<!DOCTYPE html>
<html>
<head>
  <title>Smart Irrigation</title>
  <meta name='viewport' content='width=device-width, initial-scale=1'>
  <style>
    body { font-family: Arial; margin: 20px; }
    .zone { border: 1px solid #ddd; padding: 15px; margin: 10px 0; }
    button { padding: 10px 20px; margin: 5px; }
    .moisture { font-weight: bold; }
  </style>
</head>
<body>
  <h1>Smart Irrigation</h1>
  <div id='zones'></div>
  
  <script>
    function updateStatus() {
      fetch('/status')
        .then(r => r.json())
        .then(data => {
          let html = '';
          data.zones.forEach((zone, i) => {
            html += `
              <div class='zone'>
                <h3>Zone ${i+1}</h3>
                <p>Moisture: <span class='moisture'>${zone.moisture}%</span></p>
                <p>Threshold: ${zone.threshold}%</p>
                <p>Status: ${zone.active ? 'Watering' : 'Off'}</p>
                <button onclick='waterZone(${i})'>Water (${zone.duration}s)</button>
              </div>
            `;
          });
          document.getElementById('zones').innerHTML = html;
        });
    }
    
    function waterZone(zone) {
      fetch(`/water?zone=${zone}`)
        .then(() => updateStatus());
    }
    
    setInterval(updateStatus, 5000);
    updateStatus();
  </script>
</body>
</html>
  )";
  
  server.send(200, "text/html", html);
}

void handleStatus() {
  StaticJsonDocument<512> doc;
  JsonArray zones = doc.createNestedArray("zones");
  
  for (int i = 0; i < num_zones; i++) {
    JsonObject zone = zones.createNestedObject();
    zone["moisture"] = readMoisture(i);
    zone["threshold"] = moisture_threshold[i];
    zone["duration"] = watering_duration[i];
    zone["active"] = digitalRead(zone_pins[i]);
  }
  
  String response;
  serializeJson(doc, response);
  server.send(200, "application/json", response);
}

void handleWater() {
  if (server.hasArg("zone")) {
    int zone = server.arg("zone").toInt();
    if (zone >= 0 && zone < num_zones) {
      waterZone(zone, watering_duration[zone]);
      server.send(200, "text/plain", "OK");
      return;
    }
  }
  server.send(400, "text/plain", "Bad Request");
}

Weather Integration

OpenWeatherMap API

#include <HTTPClient.h>

const char* api_key = "YOUR_API_KEY";
const char* city = "Prague,CZ";

bool willRainSoon() {
  HTTPClient http;
  String url = "http://api.openweathermap.org/data/2.5/forecast?q=" + 
               String(city) + "&appid=" + String(api_key);
  
  http.begin(url);
  int httpCode = http.GET();
  
  if (httpCode == 200) {
    String payload = http.getString();
    StaticJsonDocument<2048> doc;
    deserializeJson(doc, payload);
    
    // Check forecast for 6 hours
    for (int i = 0; i < 2; i++) {
      String weather = doc["list"][i]["weather"][0]["main"];
      if (weather == "Rain") {
        return true;
      }
    }
  }
  
  http.end();
  return false;
}

// Add to checkMoistureAndWater:
if (willRainSoon()) {
  Serial.println("Rain expected, skipping irrigation");
  return;
}

Home Assistant Integration

ESPHome Configuration

esphome:
  name: smart-irrigation
  platform: ESP32
  board: esp32dev

wifi:
  ssid: "YourWiFi"
  password: "YourPassword"

api:
  password: "api-password"

ota:
  password: "ota-password"

# Moisture sensors
sensor:
  - platform: adc
    pin: GPIO34
    name: "Zone 1 Moisture"
    unit_of_measurement: "%"
    filters:
      - calibrate_linear:
          - 2.8 -> 0.0
          - 1.1 -> 100.0
    update_interval: 30min
    
  - platform: adc
    pin: GPIO35
    name: "Zone 2 Moisture"
    # ... similar for other zones

# Valve controls
switch:
  - platform: gpio
    pin: GPIO23
    name: "Irrigation Zone 1"
    id: zone1
    icon: "mdi:water"
    
  - platform: gpio
    pin: GPIO22
    name: "Irrigation Zone 2"
    id: zone2
    icon: "mdi:water"
    # ... additional zones

# Automation
interval:
  - interval: 30min
    then:
      - if:
          condition:
            sensor.in_range:
              id: moisture_zone1
              below: 30.0
          then:
            - switch.turn_on: zone1
            - delay: 5min
            - switch.turn_off: zone1

Home Assistant Automation

automation:
  - alias: "Morning watering"
    trigger:
      - platform: time
        at: "06:00:00"
    condition:
      - condition: numeric_state
        entity_id: sensor.moisture_zone1
        below: 40
      - condition: numeric_state
        entity_id: weather.home
        attribute: precipitation_probability
        below: 30
    action:
      - service: switch.turn_on
        entity_id: switch.irrigation_zone_1
      - delay: "00:05:00"
      - service: switch.turn_off
        entity_id: switch.irrigation_zone_1
        
  - alias: "Low moisture alert"
    trigger:
      - platform: numeric_state
        entity_id: sensor.moisture_zone2
        below: 25
        for: "01:00:00"
    action:
      - service: notify.mobile_app_phone
        data:
          title: "Garden is dry!"
          message: "Zone 2 moisture is only {{ states('sensor.moisture_zone2') }}%"

Mechanical Installation

Valve Installation

1. Valve box placement

   • Plastic box 30x40cm
   • Drainage at bottom (gravel)
   • Access for maintenance

2. Valve connections

   Main supply → Main shutoff → Filter → 
   → Manifold → Valve 1 → Zone 1
              → Valve 2 → Zone 2
              → etc.
   

3. Electrical connections

   • CYKY 3x1.5 cable in conduit
   • Waterproof connectors
   • Cable labeling

Water Distribution

Main branches:

1. Dig 30-40cm deep
2. Sand bed
3. Place PE pipe
4. Cover with sand
5. Warning tape
6. Backfill

Drip lines:

Dripper spacing:
- Vegetables: 30cm
- Shrubs: 50-100cm
- Trees: around trunk

Anchoring:
- Plastic stakes every 1m
- Loop at drippers

Calibration and Tuning

Moisture Sensor Calibration

1. Dry soil: Measure value
2. Watered soil: Wait 30 min, measure
3. Ideal moisture: Per plant type (30-60%)

Watering Time Optimization

Testing:
1. Water zone for 5 minutes
2. Wait 1 hour
3. Check penetration depth
4. Adjust time as needed

Target depth:
- Lawn: 10-15cm
- Beds: 20-30cm
- Shrubs/trees: 40-60cm

System Maintenance

Seasonal Maintenance

Spring:

• Check joint tightness
• Clean filters
• Test all zones
• Calibrate sensors

Fall:

• Drain system
• Blow out with air
• Remove valves (or use glycerin)
• Winterize electronics

Regular Maintenance

• Weekly: Visual inspection
• Monthly: Clean drippers
• Seasonal: Replace filters
• Yearly: Check wiring

Advanced Features

Water Usage Monitoring

// Flow meter on GPIO25
volatile int pulseCount = 0;
float flowRate = 0;
float totalLiters = 0;

void IRAM_ATTR pulseCounter() {
  pulseCount++;
}

void setupFlowMeter() {
  pinMode(25, INPUT_PULLUP);
  attachInterrupt(25, pulseCounter, FALLING);
}

void calculateFlow() {
  // YF-S201: 450 pulses = 1 liter
  flowRate = pulseCount / 450.0 * 60; // L/min
  totalLiters += pulseCount / 450.0;
  pulseCount = 0;
}

Leak Detection

automation:
  - alias: "Water leak detection"
    trigger:
      - platform: numeric_state
        entity_id: sensor.flow_rate
        above: 0.5
        for: "00:30:00"
    condition:
      - condition: state
        entity_id: group.all_zones
        state: "off"
    action:
      - service: notify.mobile_app_phone
        data:
          title: "WARNING - Water leak!"
          message: "Flow detected with no active zone!"

Troubleshooting

Valve won't open

1. Check voltage (multimeter)
2. Manual valve test
3. Clean diaphragm
4. Check solenoid coil

Uneven watering

• Check water pressure
• Clean clogged nozzles
• Add pressure regulator
• Split into more zones

Moisture sensor not working

• Clean electrodes
• Check depth
• Replace with capacitive type
• Add corrosion protection

Price Comparison with Commercial Systems

Conclusion

Building your own smart irrigation system isn't complex and provides full control over your garden. Start simple with a few zones and gradually expand. The investment pays back in water savings and healthier plants.

Tip: Start with one test zone and once you verify functionality, expand to the whole garden.

Related Articles

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• Home Automation with Home Assistant
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