Knowing soil moisture levels can help determine when and how long to water your grass and plants, keeping you from underwatering or overwatering. Different methods for measuring soil moisture exist, ranging from using your finger to soil moisture meters and advanced moisture blocks.
Soil moisture testing methods
There are several ways to estimate soil moisture, ranging from simple rudimentary techniques to advanced devices.
Check the weight
One of the most rudimentary ways to estimate soil moisture in pots is by weight. You can lift the container and gauge its weight to determine whether the plant needs water. If it feels too light, it needs to be watered.
Obviously, this method only works if your plants are in containers or hanging baskets, and for it to be helpful, you need to know how much the container weighs when the soil is dry.
I’ll admit, this method is how I typically decide if my hanging baskets need a drink.
Use your finger
Another simple way to check the soil moisture in containers (commonly used to determine whether houseplants need watering) is to stick your finger in the soil and see if it’s dry. If the top inch or two is dry, your plant typically needs to be watered.
It’s important to remember that certain plants like aloe and low-maintenance succulents prefer the soil to dry out completely before watering again, so you’ll need to check deeper than an inch or two.
Feel and appearance
An easy way to check garden soil is to take a handful of soil from 6 to 8 inches below the surface and squeeze.
- If you can squeeze water out of it, it’s way too wet, and you’re overwatering. Chances are, you’re creating a saturated environment with little oxygen available for your plant’s roots. Conditions like this often lead to root rot.
- If it holds together when you squeeze it but no excess water drips out, and the soil doesn’t crumble off, it’s also too wet.
- If it mainly sticks together but a few pieces of crumbs fall off, the soil moisture is where you want it. This scenario is ideal – enough water for your plants to thrive, but not so much the soil is waterlogged.
For more in-depth information on this method, including guidelines for different soil types, check the helpful soil moisture feel and appearance guide by the University of Minnesota Extension.
Soil moisture meter
For those looking for a more scientific method, a soil moisture meter — sometimes called a soil probe — is a quick and simple way to measure soil moisture. It provides more information than sticking your finger in the soil or squeezing it.
To use a soil moisture meter:
- Wipe the probe clean before you start.
- Insert the probe into the soil as deep as possible and read the gauge on the meter. Depending on the type you purchased, most meters have a scale that reads from 1 to 10 or dry to wet.
- Pull it out of the ground, wipe the probe clean again, and check another spot.
- Repeat the process a few times around a given plant or within a section of your lawn. Multiple readings help give you a better understanding than testing a single spot.
Soil moisture meters vary significantly in cost. Basic meters for home gardeners typically cost between $10 and $20. Professional meters can run anywhere from $200 to $300. The more expensive meters are more accurate and durable.
Tensiometer
A tensiometer measures matric potential or water tension in the soil. This measurement indicates how much energy a plant must exert to extract water and pull it into its roots. They are typically used in agricultural or horticultural settings to help make irrigation decisions.
Tensiometers have three essential parts: a porous clay cup that goes into the soil, a water-filled tube, and a pressure gauge at the top. The clay cup is inserted into the soil, allowing water to move in and out until an equilibrium is established. The pressure gauge measures the tension or suction in the water column, indicating available soil moisture. Higher tension means drier soil; lower tension means more soil moisture.
On average, tensiometers cost between $50 and $100.
Moisture block
Moisture blocks, also known as electrical resistance or gypsum blocks, are another standard device used in agriculture and horticulture to measure soil moisture.
Gypsum blocks consist of porous gypsum material with embedded electrodes, with the entire 1-inch block typically encased in a protective coating. A wire attaches the block to a measuring meter. These blocks are buried in the soil, and soil moisture enters the block, saturating the gypsum. As the moisture changes within the block, the electrical resistance between the electrodes also changes, and the meter reads it.
The blocks cost as little as $1 or $2 each, but a meter typically costs around $300.
Time domain reflectometry (TDR)
Time domain reflectometry is a highly accurate, advanced way to measure soil moisture levels. Because of its reliability and precision, it isn’t typically used by gardeners or homeowners; it is most often used in research settings or precision agriculture.
A TDR device generates an electrical signal and sends it through steel probes in the soil. The device measures the time it takes for the pulse to travel to the end of the probe and back. The travel time is then used to calculate the soil moisture content.
The cost of a TDR device ranges from $100 to $500.
What is an ideal soil moisture percentage?
The ideal percentage depends on the plant, soil, and climate. In general, though, trees and shrubs like 20% to 40% soil moisture; vegetables prefer 40% to 80%. For grass, the percentage is based on soil type: sandy soils should be 15% to 20%, loam soils should be 35% to 45%, and clay soils should be 45% to 55%.
Why is it important to test soil moisture?
Both overwatering and underwatering can negatively impact plant growth. Testing soil moisture helps determine if you are correctly watering your garden vegetables, grass, rose bushes, or houseplants. It also helps conserve water, minimizes runoff, and improves environmental sustainability.
- Plants need a specific amount of water for optimal growth. Too much or too little water can hinder their development, reduce yields, and even kill the plants.
- Monitoring soil moisture helps determine how long to water so you’re applying the right amount of water at the right time.
- Adequate soil moisture ensures that fertilizer nutrients dissolved in the soil are available for uptake by plant roots.
- Regular checks can prevent common issues like root rot or drought stress in gardens and landscapes.
- Reduces water bills by avoiding unnecessary watering.
FAQs about testing soil moisture
How do you improve soil moisture?
The two best ways to improve soil moisture are to increase the organic matter content and mulch the soil surface. Adding organic matter like compost helps the soil retain moisture longer. Mulching with leaves, bark chips, or straw helps slow evaporation and moderates soil temperature to help hold moisture longer.
Do you need an expensive soil moisture tester for your garden and lawn?
Buying a high-end, advanced device to test soil moisture isn’t unnecessary. A $10 or $20 soil moisture meter is adequate for most homeowners. It will help you gauge if your soil is dry, sufficiently moist, or too wet so you can make watering choices for your grass, flowers, or vegetables.
Is the screwdriver test helpful for checking soil moisture?
There are online recommendations for checking soil moisture using a flat-head screwdriver. If you can easily push a four- to six-inch screwdriver into the soil, it should indicate that the soil has plenty of moisture. If it’s challenging to push into the ground, there isn’t enough moisture.
However, this isn’t a good tool (pun intended.) Soil compaction can also prevent a screwdriver from going into the ground easily. It’s better to feel it with your hands or use a soil moisture testing device.
Turn to a pro for watering advice
Testing soil moisture with these methods is a great way to help manage lawn and garden irrigation. Knowing how wet your soil is and how long it takes to dry out after watering is a fantastic tool for determining when and how long to water.
If you need help watering your yard correctly, turn to the experts at Lawn Love. We’ll put you in touch with local lawn care professionals who can help dial in your sprinkler settings.
Main Photo Credit: U.S. Department of Agriculture | Flickr | CC BY 2.0
