Learn how to use ESP32 with soil moisture sensor for smart plant monitoring, Blynk, Home Assistant, and automated irrigation projects.
What Is Soil Moisture and Why Monitor It?
Soil moisture is simply the amount of water held inside the soil.
Plants depend on the right balance — too much water can suffocate roots, too little can dry them out.
Monitoring soil moisture helps you:
- Automate watering
- Grow healthier plants
- Save water
- Prevent overwatering
- Track soil health remotely
Most modern smart agriculture systems use exactly this method.
Why ESP32 is Perfect for Soil Moisture Projects
Before jumping to wiring and code, let’s talk about why the ESP32 is so popular for soil moisture projects:
Built-in Wi-Fi & Bluetooth
Send moisture data to your phone without extra modules.
Multiple ADC Channels
Needed for reading the analog value from the soil moisture sensor.
Low Power Modes
Perfect for battery-powered plant monitors.
Works with Arduino IDE
Beginner-friendly coding experience.
Fast, reliable, and cheap
A powerful choice even for large farm-scale systems.
So if you’re wondering whether soil moisture with ESP32 is a good idea yes, it’s one of the best combinations you can build as a beginner.
Types of Soil Moisture Sensors (Which One Should You Use?)
There are two types you’ll commonly use with ESP32:
A. Resistive Soil Moisture Sensor (Cheapest Option)
This one uses two metal probes to measure resistance in wet soil.
Pros:
- Very cheap
- Easy to use
- Works with any board
Cons:
- Metal corrodes over time
- Shorter lifespan
- Readings drift with soil chemicals
Works fine for learning, but not ideal for long-term use.
B. Capacitive Soil Moisture Sensor (Most Recommended)
If you’re building a real project, use a capacitive soil moisture sensor with ESP32.
Pros:
- No corrosion
- More stable readings
- Long lifespan
- Fully waterproof PCB
Cons:
- Slightly more expensive
This sensor measures moisture using capacitance, not metal contact, so it lasts almost forever.
Recommended Model: Capacitive Soil Moisture Sensor v1.2
Best Sensor for ESP32
If accuracy and long-term use matter:
Use a capacitive soil moisture sensor with ESP32
If you’re learning quickly or building temporary projects:
Use a resistive soil moisture sensor with ESP32
But again, for real projects, capacitive wins.
Simple Theory: How Soil Moisture Sensors Work
Here’s the simplest explanation you’ll find.
Resistive Sensor
Wet soil → more electrical conductivity → lower resistance → lower output voltage
Capacitive Sensor
Wet soil → higher dielectric constant → more capacitance → different output voltage
Both deliver an analog output your ESP32 can read using its ADC pin.
Soil Moisture Sensor Connection with ESP32 (Wiring)
For Capacitive Sensor
Sensor → ESP32
- VCC → 3.3V
- GND → GND
- AOUT → GPIO 34 (ADC Input)
(Note: GPIO 34, 35, 36, 39 are input-only ADC pins.)
For Resistive Sensor (with amplifier board)
Sensor → ESP32
- VCC → 3.3V
- GND → GND
- AO → GPIO 34
Important:
Do NOT power these sensors with 5V when using ESP32.
Full Working Code: Soil Moisture Sensor with ESP32
#define SENSOR_PIN 34
void setup() {
Serial.begin(115200);
}
void loop() {
int raw = analogRead(SENSOR_PIN);
float moisture = map(raw, 0, 4095, 100, 0);
Serial.print("Raw ADC: ");
Serial.print(raw);
Serial.print(" | Moisture: ");
Serial.print(moisture);
Serial.println("%");
delay(1000);
}
This is beginner-friendly and works with both resistive and capacitive sensors.
ESP32 with Capacitive Soil Moisture Sensor (Recommended Setup)
Why everyone prefers this combination:
- Stable
- Long-lasting
- No rust
- Accurate
- Works outdoors
Calibration is simple too.
float moisture = map(raw, dryValue, wetValue, 0, 100);
You’ll measure dryValue and wetValue during calibration.
ESP32 with Resistive Soil Moisture Sensor
You can use it exactly the same way, but:
- You must avoid powering it continuously
- Use a transistor or MOSFET to switch power ON only when measuring
- Otherwise sensor probes corrode fast
Calibrating Soil Moisture Readings
Calibration makes your readings meaningful.
Step 1: Leave sensor in air
Record the raw value → dryValue
Step 2: Dip sensor in water
Record the raw value → wetValue
Step 3: Use formula
int moisture = map(raw, dryValue, wetValue, 0, 100);
Now the reading becomes real-world percentage.
ESP32 Soil Moisture Sensor Arduino Code
Here’s a slightly advanced example including filtering:
int readMoisture() {
long sum = 0;
for (int i = 0; i < 50; i++) {
sum += analogRead(34);
delay(2);
}
return sum / 50;
}
void loop() {
int raw = readMoisture();
int moisture = map(raw, dryValue, wetValue, 0, 100);
Serial.println(moisture);
delay(1000);
}
This removes noise and gives stable readings.
ESP32 Soil Moisture Sensor Project Ideas
Here are practical and fun things you can build:
Self-Watering Plant System
Motor turns on when soil is dry.
Wi-Fi Smart Plant Pot
View moisture on your phone.
ESP32 Soil Moisture Logger
Record moisture every hour.
Home Assistant Soil Dashboard
Integrates into your smart home.
Blynk App-Based Plant Monitor
See plant status from anywhere.
Automatic Farm Irrigation System
For hydroponics and kitchen gardens.
ESP32 Soil Moisture Sensor and Blynk (App Control)
This is one of the most popular setups.
Blynk lets you:
- View moisture live
- Create alarms
- Control pumps remotely
- Log data
- Set automation rules
Steps:
- Install Blynk app
- Add “Value Display” widget
- Add your ESP32 code
- Send moisture value via Blynk.virtualWrite
This gives you a clean mobile UI instantly.
ESP32 Soil Moisture Sensor Home Assistant Setu
Home Assistant is perfect for home gardeners.
What you get:
- Moisture graphs
- Automation (water the plant at night)
- Notifications
- Long-term storage
- Integration with Alexa, Google Home
ESP32 sends data via:
- MQTT
- ESPHome
- HTTP
If using ESPHome, the setup becomes ridiculously simple.
ESP32 Data to Cloud (Optional: AWS IoT)
Some users want cloud storage for serious agriculture projects.
ESP32 + AWS IoT lets you:
- Store moisture history
- Analyze crop health
- Send moisture data to dashboards
- Trigger IoT rules
Data flows:
ESP32 → AWS IoT Core → DynamoDB / S3 / Grafana
This is optional but powerful.
Battery-Powered ESP32 Soil Moisture System
You can run the ESP32 on a Li-ion battery by using:
- Deep sleep mode
- Waking every 1 hour
- Measuring moisture
- Sending data
- Sleeping again
This allows the system to run months on a single battery.
FAQ : ESP32 with Soil Moisture
1. Which soil moisture sensor works best with ESP32?
The capacitive soil moisture sensor v1.2 is the best long-term choice.
2. Why does the ESP32 give fluctuating moisture readings?
Because the ADC has internal noise.
Use averaging in code to fix it.
3. Can I power the sensor from 5V?
No. ESP32 ADC reads 0–3.3V only.
4. Why do resistive sensors corrode?
Electrical current causes electrolysis inside soil.
5. Can ESP32 work outdoors?
Yes, but use:
- waterproof box
- corrosion-protected terminals
- capacitive sensor
6. Can ESP32 send moisture data to my phone?
Yes.
You can use:
- Blynk
- Home Assistant
- MQTT
- ESPHome
7. Can I use ESP32 to control a water pump?
Yes.
Use a relay or MOSFET.
8. How often should moisture be measured?
Every 30 minutes is good.
Avoid continuous measurement.
9. Does soil type affect readings?
Yes — clay, sand, and potting soil give different ADC values.
Calibration solves this.
10. How long does a capacitive sensor last?
Years.
That’s why it’s recommended.
Troubleshooting Guide: ESP32 with Soil Moisture Sensor
Working on an ESP32 with Soil Moisture project can be exciting, but sometimes things don’t work as expected. This guide will help you identify common issues, understand the causes, and apply practical solutions. Whether you’re a beginner or an experienced maker, this troubleshooting guide ensures your smart plant or irrigation system works reliably.
1. No Reading from the Sensor
Problem: Your ESP32 shows no data from the sensor.
Possible Causes & Solutions:
- Wiring Issues: Double-check that the sensor’s VCC, GND, and AO pins are connected correctly. Capacitive sensors should use 3.3V, not 5V.
- ADC Pin Issue: Ensure the analog output connects to a valid ESP32 ADC pin (GPIO 32–39).
- Insufficient Power: Make sure the ESP32 and sensor receive stable voltage.
- Faulty Sensor: Test the sensor with a multimeter in moist soil; it should produce voltage.
2. Fluctuating or Unstable Readings
Problem: Moisture values keep jumping or flickering.
Possible Causes & Solutions:
- Electrical Noise: Long exposed wires may pick up interference. Use shorter wires or twisted pairs.
- ADC Noise: Use code averaging to stabilize readings. Take multiple samples and calculate the average.
- Environmental Factors: Extreme temperatures or direct water contact can affect sensor readings.
3. Incorrect Moisture Values
Problem: Readings do not reflect actual soil conditions.
Possible Causes & Solutions:
- Wrong Sensor Type in Code: Ensure the code matches the sensor you are using (resistive vs capacitive).
- Soil Type Variance: Different soils (clay, sand, potting soil) give different ADC values. Calibrate accordingly.
- Temperature or Humidity Effects: Monitor environmental conditions and adjust calibration if needed.
4. Corrosion on Resistive Sensors
Problem: Resistive sensors degrade over time, causing inconsistent values.
Solutions:
- Power Only During Measurement: Use a transistor or MOSFET to power the sensor only while taking readings.
- Switch to Capacitive Sensor: For long-term projects, capacitive sensors with ESP32 provide stable readings without corrosion.
5. ESP32 Not Connecting to Blynk or Home Assistant
Problem: Sensor works, but ESP32 can’t send data to apps or dashboards.
Solutions:
- Wi-Fi Credentials: Double-check SSID and password in the code.
- Network Issues: Ensure ESP32 is within Wi-Fi range and not blocked by firewalls.
- Library Compatibility: Use updated Blynk or ESPHome libraries.
- Debugging Tip: Use
Serial.println()to confirm sensor values are being sent correctly.
6. Battery-Powered ESP32 Issues
Problem: ESP32 stops functioning in battery-powered setup.
Solutions:
- Deep Sleep Settings: Configure deep sleep properly to save battery.
- Voltage Drop: Low battery voltage can cause unstable ADC readings.
- Voltage Regulation: Use a stable LDO regulator for consistent power.
7. Calibration Problems
Problem: Moisture readings do not match actual soil moisture.
Solutions:
- Measure ADC value in completely dry soil → record as
dryValue. - Measure ADC value in saturated soil → record as
wetValue. - Map readings to percentage:
moisture = map(raw, dryValue, wetValue, 0, 100); - Always recalibrate when changing soil type or sensor model.
8. Tips to Avoid Common ESP32 with Soil Moisture Issues
- Use capacitive sensors for long-term accuracy.
- Keep wiring short and shielded to reduce interference.
- Calibrate sensors regularly.
- Use averaging in software to minimize noise.
- For battery projects, configure deep sleep and voltage regulation.
- Check online guides for advanced integrations with Blynk, Home Assistant, and cloud platforms.
9. Integrating Other Sensors
For advanced monitoring, combine soil moisture with temperature sensors. For example, integrating a DS18B20 temperature sensor alongside your moisture setup provides better insights into plant conditions. Check out this detailed guide for ESP32 and DS18B20: ESP32 with DS18B20.
Final Tips for Best Accuracy
Here’s everything you need for expert-level accuracy:
- Bury sensor halfway
- Keep sensor stable (don’t move often)
- Avoid watering directly on sensor
- Calibrate properly
- Use capacitive sensor for long-term
- Use filtering in software
- Take readings every 30–60 minutes
- Don’t power resistive sensors continuously
Follow these, and your ESP32 soil moisture sensor project will be rock-solid and accurate.
If you’re exploring sensor-based projects with the ESP32, combining soil moisture monitoring with temperature sensing can take your smart garden to the next level. For example, integrating the DS18B20 temperature sensor alongside your soil moisture setup allows you to track both soil hydration and temperature for more precise plant care. You can check out a detailed guide on this setup here: ESP32 with DS18B20 to see step-by-step wiring, code examples, and practical project ideas.
Conclusion
Using an ESP32 with a soil moisture sensor is one of the easiest ways to build a smart, reliable, and low-cost plant monitoring system. With just a few components, you can track soil health, automate watering, and view real-time data from anywhere. The capacitive sensor offers long-term accuracy, while the ESP32 provides powerful connectivity and control. Whether you’re a beginner or an experienced maker, this setup grows with your skills. Start small, experiment, and let your plants enjoy smarter care.
Mr. Raj Kumar is a highly experienced Technical Content Engineer with 7 years of dedicated expertise in the intricate field of embedded systems. At Embedded Prep, Raj is at the forefront of creating and curating high-quality technical content designed to educate and empower aspiring and seasoned professionals in the embedded domain.
Throughout his career, Raj has honed a unique skill set that bridges the gap between deep technical understanding and effective communication. His work encompasses a wide range of educational materials, including in-depth tutorials, practical guides, course modules, and insightful articles focused on embedded hardware and software solutions. He possesses a strong grasp of embedded architectures, microcontrollers, real-time operating systems (RTOS), firmware development, and various communication protocols relevant to the embedded industry.
Raj is adept at collaborating closely with subject matter experts, engineers, and instructional designers to ensure the accuracy, completeness, and pedagogical effectiveness of the content. His meticulous attention to detail and commitment to clarity are instrumental in transforming complex embedded concepts into easily digestible and engaging learning experiences. At Embedded Prep, he plays a crucial role in building a robust knowledge base that helps learners master the complexities of embedded technologies.
