How to use a soil moisture meter

by | Feb 22, 2021 | Garden tools | 0 comments

I have killed more plants than I like to admit by not giving them the right amount of water.

Can you relate?

It seems like such a straightforward gardening, but it can be frustratingly difficult to master.

I have overwatered succulents and I have let mine violet leaf fig become so dry that it began to throw its leaves to the ground in protest.

A close up vertical image of a humidity sensor with a ripe tomato and leaves in soft focus in the background.

One day I saw a funny look sticking out of a friend’s bed of lettuce, and I discovered a world of soil moisture meters.

These handy tools help remove guesswork from watering.

Sure, you can stick your finger in the ground, but this is more of an art than a science, an inaccurate way of figuring out what your plants need. And with this method, you can only tell what is happening in the top few inches.

A moisture meter can tell you exactly how moist the soil is, and not just in the top few inches, but up to a foot down – or more!

In addition, you can keep your gloves on and avoid getting your fingers dirty with one of these at hand.

Thanks to my hygrometer, I do not kill plants due to poor watering.

Want to know how to put these handy garden tools to work for you? Here is what we cover:

What is a soil moisture meter?

Soil moisture meters are small hygrometers or tools that allow you to measure average moisture levels that you can insert into the soil to determine how moist it is.

A close-up vertical image of a hygrometer taking a reading of the water level in the potted plant of a houseplant depicted on a soft focus background.
Photo by Kristine Lofgren.

This provides a consistent analysis of how much water is in your growth medium so you know when it’s time for water or whether you need to endure now.

These tools typically give you a reading within 60 seconds and are simple to use.

Most of them have a small window display that shows the humidity level on a scale that typically ranges from dry to wet.

Some have a numeric scale, a color-coded face, or both to make it easy to read the humidity level. And most do not even require batteries to give you your reading!

Dr Meter Soil Moisture Meter Sensor

Dr. Meter Hygrometer

The one I trust is made by Dr. Meter. You can buy one of these at many nurseries, or via Amazon.

Some meters only measure water, but others are available that also read pH and light levels.

A close-up vertical image of a three-way hygrometer for testing pH, water and light levels depicted on a soft focus background.
Photo by Kristine Lofgren.

If you like the 3-way style that gives all these readings at once, you can pick one up at Arbico Organics.

Are these tools magical? Nix. They measure moisture by detecting electrical currents in the ground. The more moisture is available, the higher the current.

How to use one

To make this handy tool work, carefully insert the probe end into the ground so that it is buried four-fifths of the way deep. Do not force it. If you encounter resistance, try somewhere else.

A close horizontal image of a hand from the left side of the frame inserting a fork into the potted plant of a houseplant, depicted on a soft focus background.
Photo by Kristine Lofgren.

If you are using one with two probes, be sure to insert it vertically.

A close horizontal image of a hand from the left side of the frame inserting metal pins into the potted plant of a houseplant.
Photo by Kristine Lofgren.

Wait 60 seconds, then check the humidity level in the display window.

Compare the reading with the needs of your particular plant.

A close horizontal image of a hand from the left side of the frame taking a moisture reading from a hygrometer inserted into the potting mix of a houseplant.
Photo by Kristine Lofgren.

E.g, cactus and succulents like to be on the moist end of dry when freshly watered.

Cannas and Siberian irises prefer to be at the wet end of the spectrum. And some plants prefer to dry out quite a bit between waterings, while others prefer consistently moist soil.

In other words, when checking your meter, do not assume that a result that places your soil moisture in the intermediate range is ideal.

You will have drier soil for some plants and wetter for others.

If you check your cactus and it appears as a tree – or at the moist end of dry – it probably does not need water. But if you control an orchid and it appears as a three on the scale, it needs a drinking state.

After watering, let the plant sit for a minute and check the results again.

A close horizontal image of the base of the stems of a houseplant depicted on a soft focus background.
Photo by Kristine Lofgren.

When done, remove the probe, wipe it off, and store it.

Do not leave it in the ground because the probe degrades quickly.

A close horizontal image on the sensor is a tool for monitoring potted plant pots.
Photo by Kristine Lofgren.

Do you see these two probes? One was left in the ground for a month (okay, maybe more like three months. What? I got busy) while the other was removed consistently after use and cleaned.

Troubleshooting tips

Although these are fairly simple tools, they are still prone to problems. Sometimes a probe fails to read, or the needle may bounce around like a rabbit after dipping a pot of coffee.

If you insert the probe and the needle does not move, remove it and wipe the probe clean. DO NOT put it in a container with water to see if it works. The probe does not work in water and is only intended for use in soil.

Instead, soak some soil thoroughly with water to make a test. It should be completely saturated so that it drips water if you take a sample. Then insert the probe. If it still does not read, it may be defective.

If the needle bounces around and does not fold, it may touch some metal or rock underground. Pull it out and sink it somewhere else.

Remember, never leave the meter in the ground for several days or weeks. This can damage the probe.

I also recommend checking the ground with your finger every now and then to confirm that the meter is working. Do not rely solely on the hygrometer.

If your plant seems to be falling out, you can stick a finger in the ground as a point of comparison. The meter may say moist, but the soil is actually dry if it is not working properly.

A soil moisture meter can work incorrectly if you have a high salt content in your soil. This can happen if you water from the bottom of a container or if you use a fertilizer with salts in it.

If your soil is salt water, you will get an incorrectly high moisture reading, which is why it is important to physically check with your finger if you suspect that the reading is incorrect.

Take the guess out of watering

Hygrometers are incredibly practical. What’s easier than just sticking something in the ground and knowing within a minute if your plant is dying after a drink or needs time to dry out?

A close-up horizontal image of a black plant pot with a sensor placed in the ground to test the condition of the soil, depicted on a soft focus background.
Photo by Kristine Lofgren.

If you are wondering which moisture meter works best, we have an overview of the best models that can help you (coming soon!).

Was this article helpful to you? In that case, you might want to visit some of our other tool guides next door to make gardening easier:

Photos by Kristine Lofgren © Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Product images via Arbico Organics and Dr Meter. Uncredited photos: Shutterstock.

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About Kristine Lofgren

Kristine Lofgren is an author, photographer, reader and gardener outside of Portland, Oregon. She grew up in the Utah Desert and made her way to the Northwest Pacific rainforest with her husband and two dogs in 2018. These days, her passion is focused on growing decorative edible foods and searching for food in that urban and suburban landscape.

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