Plant grow: Soil relative humidity control
If you plan to make a smart growing system to water plants on traditional soil like pea you will need soil moisture sensors, or other methods to control the soil moisture. That does not happen when you grow plants on non-traditional watering systems like hydroponics. In hydroponics cultures where water is continuously flowing around the roots monitoring the soil moisture does not make sanse.
But on traditional watering systems if we can’t control the soil moisture we won’t make any stable plant watering system, and on the long run, bad watering timing will lead to major problems and diseases for the plants we grow.
To control soil humidity we will need soil moisture sensors: on this post we are going to cover the market available options for Arduino and Raspberry like boards:
Resistive sensors
For a resistive sensors complete guide
First resistive soil moisture sensor for Arduino
Price range: around 0.5$ on Aliexpress.com
This were the first ultra-cheap soil moisture sensors used on Arduino-like devices, they worked…for a while. This sensors present a major flaw: in no time they get corrosion due to electrolysis and of course, it will malfunction soon. To get an idea, they are not reliable after a month. So new versions were developed:
This were the first ultra-cheap soil moisture sensors used on Arduino-like devices, they worked…for a while. This sensors present a major flaw: in no time they get corrosion due to electrolysis and of course, it will malfunction soon. To get an idea, they are not reliable after a month. So new versions were developed:
Gold immersed resistive soil moisture sensors for Arduino
Price range: around 1$ on Aliexpress.com
The sensor proves come with a layer of gold to avoid corrosion. They certainly last longer than the first ones, but still it’s a clunky design with exposed connectors and wires.
Corrosion resistance soil moisture sensors
Price range: from 2$ to 7$ on Aliexpress.com
This is the best choice in terms of price, durability and accuracy. It is the first ready-to-use Soil Moisture Sensor: sealed connectors and pins with a robust protection, plastic covers on the sensor proves to avoid any corrosion.
Capacitive sensors
Capacitive Soil Moisture Sensor v1.2
For a capacitive sensors complete guide
Price range: around 1$ on Aliexpress.com
This sensors use another materials to achieve similar results, but they are more accurate than the first resistive sensors. But still present this very clunky design with exposed electrical components and connections, which will soon lead to malfunction.
Alternatives to direct soil moisture monitoring
Alternative feasible options to soil moisture sensors use two concepts: air relative humidity nearby soil and soil weight.
Monitoring the relative humidity nearby soil: Reliable sensors of air relative humidity can be placed nearby soil and get an approximated measure of the soil humidity.
Monitoring the weight of the soil or the plant pot as a measure of how many water is trapped within the soil. This may be one of the most simple solution for conventional watering systems. If we know how much the soil weight on dry state, with a few test, we can build a weight scale from dry soil to flooded soil. With this, we can know exactly how many water remains on the soil, and thus, the soil relative humidity. As the plant grows corrections on the scale may be needed, tuning this scale taking into account the plant grow and its weight gain is not a major problem, plants grow fairly slow.
