How to Use a Moisture Meter for Your Plants

Soil moisture meters are small handheld devices that can be used to measure the moisture content in your plant’s soil in order to give you an indication of whether it's time to water your plant or not. 

While it seems straightforward, watering your plants properly is one of the most important, and most difficult, parts of keeping your plants happy and healthy. Overwatering and underwatering are some of the quickest ways to kill a plant, and it can often be difficult to identify what is going wrong until it's too late. 

Let's face it, there are a lot of different factors that go into how often you should water your plants. The type of plant, soil conditions, time of year, lighting conditions, temperature, and humidity are just a few different factors that can impact a watering schedule. It is possible to evaluate soil moisture by manually feeling the soil, usually by pressing one or two fingers down into the soil. However, you can usually only measure a couple of inches down, and this doesn’t give you a good idea of the average moisture content in your entire container. Moisture meters help take the guesswork out of watering your plants by providing accurate readings of the moisture content in your plant’s soil. 

Why Use a Moisture Meter?

For those who struggle with watering their plants appropriately, a moisture meter is a handy tool that can help prevent overwatering or underwatering. No need to stick your fingers in the soil of your plants in an effort to guess whether the soil is dry or not anymore—a moisture meter can give you a definitive answer. Plus, a moisture meter reads more than just the top few inches of soil. The reading given is accurate for up to a foot below the surface. 

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How Do Moisture Meters Work?

Moisture meters use the principle of electrical resistance to measure the conductivity of the soil. Simply put—because water conducts electricity well, high moisture content in the soil is measured by higher electrical currents, whereas lower electrical currents indicate drier soil. Some moisture meters can even read the light conditions around a plant as well as the soil pH. These meters are called three-way meters. 

1. Push the Metal Probe Into the Soil

   Gently push the metal probe about ⅘ of the way down into the soil. If you meet resistance, remove the probe and try another spot. You don’t want to force it as the probe is sensitive.

2. Wait 30 to 60 Seconds

   Moisture meters normally give a reading within 30 to 60 seconds. If you don’t see a reading after 60 seconds, remove the probe, gently wipe it down, and try again in a different location.

3. Read the Results

   Once the results are ready, moisture meters are easy to read. Depending on the model and brand of moisture meter, they may provide results in the display window on a numerical scale or a scale of dry to wet. The scales are often color-coded to provide additional clarity.
   

How to Interpret the Results

You’ve measured the moisture of your soil using a moisture meter—now what? Next, it's time to interpret the results and decide whether it’s time to water your plant. Unfortunately, as handy as moisture meters are, they cannot tell you whether it’s actually time to water. In order to figure this out, you will need to be familiar with the needs of your unique plant. 

For example, a result on the dry end of the scale will mean different things for different plants. For cacti and succulents that are perfectly happy in dry soil, you may choose to wait a bit longer before watering, especially if they don’t get prolonged periods of direct sunlight. However, for plants like pothos and philodendron, a dry reading means it’s time for water. Further still, some plants like ferns and calatheas like to sit in consistently moist soil and shouldn’t be allowed to dry out at all. Make sure you have an idea of what your plant needs before you decide whether it’s time to water or not based on a reading from your moisture meter.

How to Clean and Store a Moisture Meter

Once you have finished using your moisture meter, remove it from the soil and gently wipe it down with a clean, dry cloth. Moisture meters should never be left in soil when they are not in use as this will degrade the sensitive probe. Store your moisture meter in a dry location between uses. 

Common Problems With Moisture Meters

Handheld moisture meters are generally pretty reliable and straightforward devices, however, there are a few common problems that you may encounter while using these meters. First, it is possible that you may not receive results from the moisture meter after 60 seconds in the soil. If this happens, remove the metal probe from the soil, wipe it down with a clean dry cloth, and try again in a different location. Do not submerge the probe in water to test if it works—moisture meters are designed to work in soil only and will not provide a reading in water. Second, if the needle in the display window is bouncing around and does not settle, the probe could be touching a small rock or piece of metal in the soil. Remove the probe and try again in a different location.

It is also important to know that because moisture meters work by measuring electrical currents within the soil, soil that has a high salt content will result in inaccurate readings. For this reason, take the results with a grain of salt (pun intended), and if you are unsure about whether a reading is accurate, try manually feeling the soil as well as a backup.