If you’re relatively new to gardening, you’re growing in pots or have plants such as succulents that need the soil to dry out between watering, you might consider investing in a soil moisture meter. But, how do soil moisture sensors work?
As the most basic explanation, a soil moisture sensor features a probe that you insert into the soil and then gives you a reading on the moisture content.
While there is plenty of technical advice available for using advanced soil moisture sensors in agriculture, I thought I would simplify all that technical jargon and explain how soil moisture meters can be useful in a home garden.
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What Is A Soil Moisture Sensor?
Essentially, soil moisture sensors have been used extensively for years in agriculture and are often connected to irrigation systems. They are very useful for crop growing and can help to initiate the irrigation of crops to increase crop yields.
These sensors are much more advanced than those available for home gardens. They measure the soil water tension to initiate irrigation. Put simply, soil water tension is a level of force required for plants to extract moisture from the soil. Essentially, they determine how much available water there is in the soil.
More recently, soil moisture meters have been available to gardeners all around the world. They’re a useful tool to let you know when your plants need water. This means that you can be extremely water-wise. You only need to water your plants when the surrounding soil is at a certain moisture level.
A soil moisture meter is a much more accurate way to test the soil water content rather than just using your finger. It can be used out in the garden but can also be extremely useful when you’re growing in pots.
However, it won’t accurately tell you how much water is in the volume of soil that you’re testing. It will only give you an indication of the soil moisture level so that you can determine if you need to water.
This simple soil moisture sensor has a probe that you stick into the soil. They generally look very similar to the meat thermometer that you have in your kitchen.
Most models available for the home gardener will then give you a digital display that tells you the moisture content in the soil. Some models just have a dial that shows you how much moisture is in the soil.
While these sensors are not as advanced or precise as those used in agriculture, they can still give you a good indication of the moisture level in the soil. This means you can take the guesswork out of your watering routine.
Who Benefits Most From Using A Soil Moisture Sensor
If you’re just fairly new to gardening or growing your own produce, you might not yet know how much and when to water your plants.
By testing the moisture content in the soil, you can easily decide when it’s time to water. You can also see if you should hold off because there’s still enough moisture in the soil.
Soil moisture meters are also ideal for gardeners who grow primarily in raised garden beds, pots and even grow bags. Growing in pots or raised beds often means that the soil may dry out faster than the ground soil.
For this reason, you might want a better way to test the moisture content in the soil.
Succulent growers would also benefit from investing in a soil moisture meter. This is because many succulents have very definite water requirements. Most of them need the soil to dry out completely before more water is added.
Even experienced gardeners can benefit from using a soil moisture sensor. This can be useful if you have a plant that is not thriving and you’re trying to diagnose what’s wrong with it.
Water-wise gardeners will also find this tool very useful. This means you can avoid irrigating your garden when it doesn’t really need it. This saves water and prevents excess water from running off and ending up in the surrounding natural water catchment areas.
The Different Types of Soil Sensors Or Moisture Meters
If you visit a hardware store or browse online, you’ll probably be confronted with a range of different types of soil moisture sensors. These may have sensor probes suitable for different depths of soil.
There will be sensors with short probes of around 4 to 12 inches (10 to 30 cm). These are perfect for testing the soil moisture content of your container-grown plants.
You’ll also find moisture sensors that have much longer probes, even up to 40 inches (1 metre) in length. These can be used out in the garden to test the moisture level deeper down in the soil.
There are even more advanced models available. These can test other things like the soil pH. This can be very useful when you’re growing plants that need either acidic or alkaline soils to thrive. Some can even measure soil temperature so that you know exactly when to plant your summer vegetables.
How Do Soil Moisture Sensors Detect How Much Moisture Is In The Soil?
There are a couple of different ways that a soil moisture sensor can measure the amount of moisture in the soil.
Using Conductivity
Some soil moisture sensors work by measuring the conductivity in the soil. These are known as resistive soil moisture sensors. Inside the probe that you stick into the soil of a resistive soil moisture sensor, there are two electrodes. These measure how much electrical current flows between the two.
As the soil dries out, the conductivity decreases because higher resistance is created. This is because dry soil has many more air pockets and air is a relatively poor conductor of electricity.
On the other hand, water is a fairly good conductor of electricity. As the moisture content in the soil increases, conductivity increases. This is because there is lower electrical resistance between the conductors in the probe.
Using Capacitance Or A Capacitive Sensor
But, it gets a little more technical than that. Many soil moisture sensors use capacitance to measure the water content of the soil. In simple terms, a capacitive soil moisture sensor has circuits inside the probe. These collect and store energy in the form of an electrical charge.
The amount of energy the probe collects directly responds to how much moisture is in the soil.
How To Read A Soil Moisture Meter
The simplest soil moisture meters just have an analog output with a dial with numbers ranging from 1 to 10. The lower numbers reflect wet soil while the higher ones tell you that the soil is dry.
Ideally, soil moisture in the range of 4 to 6 is optimum for healthy plant growth.
To measure the moisture content in the soil, all you have to do is stick the probe into the soil near the root zone. Then, wait to see what number the needle on the dial points to.
There are also slightly more advanced soil moisture meters that have a digital output which are extremely easy to read.
A Word Of Advice From An Expert Gardener
I’ve been gardening for nearly 50 years and when I first started, soil moisture sensors were not available for home gardeners.
This meant that I had to use more traditional methods to test the moisture content in the soil. Usually, this just involved sticking my finger into the soil and seeing whether it was wet or dry.
So, while I do recommend that new gardeners will benefit from using a soil moisture sensor, I also suggest that you get to know your soil type to understand how and when you should water.
For example, sandy soils tend to dry out more quickly, so they’ll need watering more often. But, if you amend the soil with lots of compost or organic matter, you’ll improve the water-holding capacity. This means that the amount of water you use each time can be reduced.
On the other hand, clay soil tends to hold moisture much better. But, this can also be a problem if you get a lot of rain or have the propensity to overwater.
Similarly, soil in pots does tend to dry out far more quickly than ground soil. Often, however, the weight of the pot should tell you whether the soil is dry or not. Wet soil is far heavier than dry soil.
So, while soil moisture sensors can be a valuable aid relying on them too much may mean you’ll never learn how to read the plants in your garden. This is one of the most fascinating parts of growing plants.
Some plants will even tell you when they need water because you’ll notice them physically wilting a little. While this can be quite alarming at first, don’t worry too much. As soon as you give them a good drink, they’ll perk right up again.
Frequently Asked Questions
Moisture meters are a good tool for novice gardeners. They can help you to determine when your plants need water. They can help you to understand the water-holding capacity of your soil better. Plus, they can also assist in determining the correct water use for your particular soil.
One of the best ways to test if your soil moisture sensor is working is to test it in a pot filled with a completely dry soil sample. Then, just wait to see what the reading is.
If you don’t have a soil moisture meter, using your finger is one of the best ways to test soil moisture. Poke your finger into the soil up to the first knuckle. If soil sticks to your finger as you pull it out, there is moisture in the soil. But, if your finger comes out clean, then the soil is dry.
Ideally, you want to push the probe in as far as it will go. This will allow you to test the soil moisture content for the plant roots.
No, once you’ve finished using the moisture meter, you should remove it from the soil. You should also wipe the probe with a cloth. If you leave it in the soil it will deteriorate and you won’t get accurate readings.
Absolutely! If you’re conscious about your water consumption, a soil moisture meter can help you to reduce how often you water.
Final Thoughts
Soil moisture sensors can be a useful tool for novice gardeners or those who like to grow in pots. They can also be very useful for people who grow succulents that have very specific water needs.
In general, they work by measuring the conductivity in the soil and this determines the moisture content. While these sensors can be quite helpful for you to learn when your plants need to be watered, it’s also a good idea to get to know your soil environment.
Understanding how your soil holds moisture can help you to better determine when your plants need to be watered. Plus, you’ll also know when watering is not a good idea or even a waste of a precious resource.
