Moisture meter for plants

Contents

Take the Guesswork Out of Watering with a Moisture Meter

Keep reading to learn how to properly water plants! Watering is one of the most common culprits behind plant decline, be it over or under watering. Think about it; the symptoms of each are similar… wilting, yellowing leaves, maybe a few brown leaves. It’s easy to see a plant struggling and think, ‘well, I just need to water it more.’ Hold up! Whether the plant is in your landscape beds or in your favorite planter by the kitchen sink, every time a plant is struggling, it’s time to do some investigating. Keep reading for the water-related part of the investigation below. Remember to always check the entire plant over for signs of injury, disease or insect damage as well.

How to Use a Moisture Meter

In regards to watering, your first instinct may be to touch the top of the soil. And while that isn’t a bad place to start, it won’t tell you the whole story. This is because majority of plant roots are deeper than the soil surface. This is where a Moisture Meter comes in very handy. Place the sensor, located in the tip of the Moisture Meter, into the soil. If the plants are in a shallow planter, try to place the tip two thirds of the way down. Same if the plant is in a small pot. For deep pots, plants in landscape beds or lawn areas, push the sensor down into the soil as far as possible.

How to Read a Moisture Meter

As you can see in the above image, our Moisture Meters shows a range of 1 to 4, with 1 indicating dry soil and 4 indicating wet soil. On the back of the packaging, you will see each of these numbers, followed by a list of plant materials. This is to give you an idea of the moisture level that many plants prefer. Water when the indicator number is less than the preferred number they are listed under. Don’t see your plant on the list? With so many plants out there in the world, not all can be listed. If your plant isn’t on that list, ask us and we can offer a recommendation.

Bottom line, different plants have different needs; a holly is going to require less watering than a shrub, annual or tropical in full bloom. A cactus or succulent plant that has water storage in the leaves needs less water than a tropical plant native to a much wetter environment.

How to Check Soil Drainage

Another thing to consider; through analyzing and investigating your plants’ water needs, you will learn how well your soil drains. You might think there is no way the plant is getting too much water while in fact, it’s not a matter of how much water the plant is given, it’s about how long the soil holds the water. Most of our common landscape plants, lawns and houseplants like moist, well-drained soils. Many of our landscapes have heavy, poorly draining soil… the result is too much water resulting in a lack of oxygen for plant roots. This situation might require amending the soil as well as altering your watering schedule.

Learn When to Water

Think of Moisture Meters as a training tool. Once you get into a habit of using it appropriately, you will learn how your lawn, landscape beds, annual color and potted plants absorb water. This will help you learn when to water plants. It will also help establish a watering rhythm with both your existing plants and new plantings. And at only ten bucks, they are a pretty low risk, high return investment, wouldn’t you agree?

For more information on how to water plants smarter, visit our blog post.

Matilija Nursery – California Native Plant and Iris Nursery

How to Water-Get a Moisture Meter!

(You moisture meter is your friend – Matilija Bob)

I don’t know what it is this year, but how to water “correctly” is problem number 1! The basic instruction is: give your new plants a deep watering, down to the roots. Then let them go dry, even for a day or two. It doesn’t mean, turn your sprinklers on daily, or leave the dripper on 3x per week for 8 minutes, or anything like that.

Here’s a little more detail on how you should be watering. To give your new plants a deep watering down to the roots, how long do you have to water and how often? If you just look at the top of the soil, it could look wet, but the roots are still dry; or the day after you’ve watered, the top of the soil could look dry when the roots are still wet. What to do if eyes lie?

It’s now time to whip out your decoder, the moisture meter that will help you answer these questions and put you on the right road to taking care of your new plants. Ready? Go to your garden or home improvement store with a garden department and buy a moisture meter that looks like the one shown below. The one shown below is the luxury model and measures moisture, light, and ph. It also has a long probe (in this case 2 long probes). This long probe is what you’re looking for and it should set you back about $8 with tax.

Plant your new plant properly, getting things off to a good start. This means dig the hole and fill it up with water and water the plant in the pot too. Watering the hole makes the whole area damp and watering the plant in the pot tends to reduce transplant shock and lets the plant slide out of the pot more easily, without breaking the roots. Now take your new plant out of the plastic pot without breaking the roots and place the plant in the hole, cover it in/backfill, and water heavily.

The next day, come out to your new plant in the garden and stick the probe from your new moisture meter all the way into the ground (about 1 FOOT AWAY FROM STEM). Be careful not to stick the probe through the root ball.

If your moisture meter reads wet the day after you’ve watered, you’re doing the right thing. If it reads moist then you should have watered a bit longer but don’t water again until it reads dry. So when it reads dry just water a bit longer and go through the process again. In most cases you’ll be watering between 1x and 2x per week if you plant in the summer. If you plant in late fall or winter you’ll probably be watering 1x per week and most likely that’s it. When it rains you’re off the hook but after about a week or so check things out with your moisture meter and if it’s dry then deep water again.

The moisture meter inserted at the “edge” of the pot is reading moist. We’ll check it again in a few days then water again. This next reading was taken at one of the plants we planted in our butterfly/hummingbird garden.

The plants have been in the ground for a while and the roots are deeper than the probe, still we should deep water in the next couple of days.

If you do this a few times you’ll get the hang of it. The basic idea is that water needs to get to the roots but the roots for native plants can’t be moist all the time and need to dry out. If they stay “moist” all the time you’ll just rot the roots and your plant and new landscape will just kick the bucket. Some plants need to go dry for a fairly long period of time in the summer. They’re in somewhat of a dormant state and even a deep watering 1x will not have a good result so if your not sure, check with the nursery on basic watering as a double check. As an example we water white sage (Salvia apiana) 2x per month when they’re in their pots at the nursery. We do the same with pacific coast irises.

That’s it, now go spend $8 or less and get a moisture meter, use it and it will set you free!

Measuring Soil Moisture

It is common landscape practice to supplement rainfall with the use of an irrigation system to keep plants looking their best. Many systems are automatic: the more complex units are connected to a climate-based electronic controller and run when weather and evapotranspiration data dictate; the simpler ones run a set schedule linked only to a time clock. Either of these systems may apply more water than is necessary to maintain a healthy landscape. For a clear picture of when and how much to water plantings, agricultural managers have long relied on soil moisture measurements; landscape professionals can do the same to maximize irrigation efficiency in landscape and turf plantings.

Soil Moisture Terminology

The following terms are commonly used to describe how soil moisture is quantified. More detailed information on all of these can be found in the agricultural extension publications listed under Resources.

  • Soil water content is a measurement of the amount of water in a known amount of soil; it can be expressed as % water by weight or volume of soil, or inches of water per foot of soil.
  • Soil water potential or soil moisture tension is a measurement of how tightly water clings to the soil and is expressed in units of pressure called bars (one bar is equal in strength to the pressure of one atmosphere). Generally the drier the soil, the greater the soil water potential and the harder a plant must work to draw water from the soil.
  • Plant available water (PAW) is the amount of water in the soil between the soil’s field capacity (soil water content after gravity has removed any freely draining, excess water) and its permanent wilting point (soil water content at which most plants can not recover from wilting). It is expressed as inches of available water per foot of soil.

    This figure is important because it is within this range (between field capacity and wilting point) that irrigation should occur, based on the amount of PAW that can be depleted in the soil without harming plant growth and development. Plants with shallow roots and low root densities should be watered before the soil moisture level comes too close to the permanent wilting point since they will be less able to absorb all available water than plants with deeper roots and higher root densities.

    A useful tool for estimating PAW in different soil types is a hydraulic properties calculator, which is readily available online. The calculator is straightforward, but requires the user to know the percentages of sand and clay in his or her soil. This kind of soil textural analysis can be requested in a soil test from the Soil and Plant Tissue Testing Laboratory at UMass (https://ag.umass.edu/services/soil-plant-nutrient-testing-laboratory).

A wide range of tools are available for determining soil moisture, and the devices mentioned here are typically used for irrigation management purposes. They are not much more expensive than simple soil probes (but are much more accurate), and are straightforward to operate.

  • Tensiometers are devices that measure soil moisture tension. They are sealed, water-filled tubes with a porous ceramic tip at the bottom and a vacuum gauge at the top. They are inserted in the soil to plants’ root zone depth. Water moves between the tensiometer tip and surrounding soil until equilibrium is reached, and moisture tension registers on the gauge at the top of the unit. Readings indicate water availability in the soil. Tensiometers operate best at soil moisture tensions near field capacity and need to be serviced before reuse if they dry out. Average cost for a tensiometer is $50-$100 (and generally more than one is installed at a location) (Cregg, 2003).
  • Electrical resistance blocks, also known as gypsum blocks, measure soil water tension. They consist of two electrodes embedded in a block of porous material, usually gypsum; the electrodes are connected to lead wires that extend to the soil surface for reading by a portable meter. As water moves in or out of the porous block in equilibrium with the surrounding soil, changes in the electrical resistance between the two electrodes occur. Resistance meter readings are converted to water tension using a calibration curve. Gypsum blocks operate over a wider range of soil moisture tensions than tensiometers, but tend to deteriorate over time and may even need to be replaced yearly (Werner, 2002). Individual blocks can cost as little as $1.25 each and the meter is around $300 (Cregg, 2003). Granular matrix sensors are newer devices that are similar to gypsum blocks but are less susceptible to degradation. The sensors are more expensive than gypsum blocks, in the $30 range.
  • Time Domain Reflectometry (TDR) is a newer tool that sends an electrical signal through steel rods placed in the soil and measures the signal return to estimate soil water content. Wet soil returns the signal more slowly than dry soil. This type of sensor gives fast, accurate readings of soil water content, and requires little to no maintenance. However, it does require more work in interpreting data, and may require special calibration depending on soil characteristics. The cost ranges from $100 to $500 (Ling, 2005).

Resources

For more information about the theory and practice of measuring soil moisture, refer to the following extension publications:

  • Cregg, B. 2003. Soil moisture measurements in nurseries and landscapes. Crop Advisory Team Alert, Vol. 18, No. 12. Michigan State University Extension, East Lansing, MI.
  • Evans, R., D. Cassel, R. Sneed. 1996. Measuring soil water for irrigation scheduling: monitoring methods and devices. Publication Number: AG 452-2. North Carolina Cooperative Extension Service. Raleigh, NC.
  • Ling, P. 2005. A review of soil moisture sensors. Vol. 12, Issue 3. Ohio Floriculture Online. The Ohio State University Extension. Columbus, OH.
  • Scherer, T., B. Seelig, D. Franzen. 1996. Soil, water and plant characteristics important to irrigation. EB-66. North Dakota State University Extension Service. Fargo, ND.
  • Werner, H. 2002. Measuring soil moisture for irrigation water management. FS876. South Dakota State University Cooperative Extension Service. Brookings, SD.

Written by: Jennifer Kujawski
Revised: 09/2011

What is Used to Measure Moisture in Soil

For farmers, there are few things as important as the quality of soil. If the soil they’re trying to grow crops in is depleted of nutrients, then crops will not grow well. Additionally, the amount of moisture in soil can have a major effect on crop quality: Too little water can stunt plant growth and reduce quality, while too much water can wash away fertilizer and soil nutrients.

To maintain soil health and quality, farmers need to not only rotate crops and use fertilizer to replenish lost nutrients, they also need to closely monitor and control the moisture content of their soil as well. The question is, how can farmers measure soil moisture?

One of the most accurate and reliable ways to measure the amount of water in soil is to use a soil moisture meter.

What is a Soil Moisture Meter?

The short answer is that it is a type of agriculture moisture meter designed specifically to monitor the amount of available moisture in soil at a specific depth. However, these devices are a bit different from the typical moisture meter.

The pins on a normal moisture meter would not penetrate deep enough into soil to provide any kind of useful estimate of available moisture. Also, because soil composition can vary so much from one region to the next, there is no standardized soil “scale” that could reliably give a precise moisture content (%MC) measurement in soil.

Since moisture meters use electrical resistance to measure moisture content, slight differences in electrical conductivity caused by soil having different contents can throw off moisture measurements.

So, How Do Soil Moisture Meters Work?

To get a measurement of the available moisture in soil, soil moisture meters use a specially-designed sensor block that is buried deep in the soil. The exact depth for installing the sensor block will vary based on the active root zone of the crop. For best results, most farmers install two sensor blocks, one at a “shallow” depth and one at a “deep” depth.

By using sensor blocks at two different depths, farmers can better gauge the effectiveness of their irrigation techniques and avoid wasting water.

The sensor blocks that are used with Delmhorst’s KS-D1 moisture meter are made of gypsum, a water-absorbent material. When buried in the soil, the gypsum blocks will slowly reach a state of equilibrium with the moisture content of the surrounding soil.

The electrode inside the sensor block measures the amount of moisture the block has absorbed—and, because the block itself is made of a specific material (gypsum), it is easier to accurately gauge the available moisture in the soil that a crop’s roots could absorb.

Once the sensor blocks are installed and have reached equilibrium with the surrounding soil, farmers can plug the electrode into their soil moisture meter and take a reading whenever they want.

Using a Moisture Meter for Soil

Some general tips for using a soil moisture meter include:

  • Using a 1-inch soil auger to dig the initial hole.
  • Creating a creamy slurry, consisting of soil and water, to place into the bottom of the hole prior to installing the sensor block.
  • Using two sensor blocks—a “deep” block and a “shallow” block—and marking their electrode leads off so you know which is which.
  • Lightly tamping down the soil little by little as you backfill each hole after installing the sensor blocks.
  • Tying the electrodes to a stake so they aren’t lying in the dirt.
  • Installing other stations of electrodes about 10 inches – 20 inches away from the first.
  • Avoid installing electrodes directly next to sprinkler systems or in areas that are significantly higher or lower than the rest of the field.

Want to learn more about using moisture meters for soil? Or, do you need help finding the right kind of meter to use? If you have any questions, please contact Delmhorst, or leave a comment below!

Topics: moisture meters

Soil Moisture Measurement Instrumentation

Abstract

A review of some of the techniques available for the determination of soil moisture content as a tension or a volume is offered. The method of determining soil moisture content by the different techniques is described with attention given to the neutron probe (NP), time-domain reflectometry (TDR) and frequency domain (Capacitance) techniques in particular. The choice of instrumentation for soil moisture determination will depend on the consideration of factors such as: physical limitations of different techniques; the level of information required (either an absolute or relative moisture measurement); the amount of data needed to objectively decide upon an irrigation regime (with consideration to spatial and temporal problems); the initial cost of the instrument and sampling; the reliability of the instrument and the collected data; and, the ease of use of the instrument in the field.

Introduction

Moisture content of the soil is a major factor determining plant growth1, especially in irrigated systems. Currently there are many and varied methods for determining soil water content on a volume basis (qv, m3m-3) or a tension basis (kPa or bar) as described by Gardener2.

The basic objective of irrigation scheduling is to minimise water stress of the plant, that of over irrigation, and under irrigation. The manager aims to manipulate the biological process of cell elongation and cell reproduction for improved plant yield3 and maximum use of available effluent.

In optimising plant cell reproduction and growth (cell expansion), the ability to monitor the soil moisture content is the principal facet of developing good water management programs. A tendency to over or under-irrigate results due to the absence of information about the soil moisture status down the soil profile. The result of over irrigation is poor utilisation of natural rainfall because of high surface run off, and production problems associated with excessively wet soil such as waterlogging, leading to recharge of underlying aquifers, leaching of nutrients, increased incidence of plant disease and reduced daily water use. The reduced daily water use of plants increases the area of irrigated land required to dispose of a given volume of water increasing the capital cost of land based waste water disposal systems.

The decline of soil water content will result in a decrease of photosynthesis and cell expansion of the plant. Under-irrigation will result in stress being placed upon the plant root water uptake mechanism to maintain transpiration rates. A subsequent reduction in daily water use and cell production will occur with decreasing soil moisture content. Ludlow et al. 3 showed that stem elongation rate declined ( in Cajanus cajan) at a linear rate after 10% of available water was utilised by the plant until elongation was 40% of the maximum rate as the plants approached wilting point.

To develop an irrigation scheduling program the basic requirement is the ability to regularly obtain objective data. The ability to accurately measure soil water content, plant size and condition is an integral mechanism in the process of developing an irrigation scheduling program that allows a better understanding of plant and soil water relations. From this basis, an understanding of plant agronomy is developed with an appropriate computer interface giving the manager a better working knowledge of what is happening to the applied irrigation and its relation to plant water use and soil moisture status.

Instruments Available for Objective Measurement of Soil Moisture Content

Objective soil moisture measurement can be undertaken with simple tools, such as a shovel, or complex tools that record measurement of soil moisture on a volumetric basis. The method of measurement is simply a device allowing moisture determination in an objective fashion. It is important that measurements are made regularly and recorded systematically to allow improvement in irrigation scheduling and soil/plant management decisions.

There are different methods available for development of an irrigation scheduling program using different tools to collect relevant information and present the data to the irrigation manager.

The Neutron Probe (NP)

An established technique that is used extensively throughout Australia by farmers, consultants and researchers. The technique is based on the measurement of fast moving neutrons (generated from an Americium 241/Beryllium source) that are slowed (thermalised) in the soil by an elastic collision with existing Hydrogen particles in the soil. Hydrogen (H+) is present in the soil as a constituent of:

  1. soil Organic matter
  2. soil clay minerals
  3. water

Water is the only form of H+ that will change from measurement to measurement. Therefore any change in the counts recorded by the NP is due to a change in the moisture with an increase in counts relating to an increase in moisture content.

In the field aluminium tubes are inserted into the soil and stopped to minimise water entry. Readings are taken at depths down the profile (e.g. 20, 30, 40, 50, 60, 70, 80, 100 and 120 cm) with a sixteen second count. The three aluminium tubes are then averaged to counter the effect of spatial variability reducing the value of the measured moisture content data.

Measurements are taken two to four times a week and information is down-loaded to a personal computer for interpretation. Use of the NP technique for vadose (unsaturated) zone monitoring has been employed to determine contaminate leak detection along specific transport pathways5, and to monitor land disposal of effluent with the NP technique6.

Time-Domain Reflectometry

Determines the apparent dielectric (Ka) of the soil matrix and this is empirically related to the volumetric soil moisture content7. The method is quick, relatively independent of soil type, non destructive, suited for surface and profile measurements, and allows repeatable in situ measurement. The TDR is a portable unit that can be carried allowing point soil moisture measurements or linked to a multiplexer to measure an array of buried waveguides8. The moisture content determined by the TDR is the average moisture along the length of the waveguides. Therefore, to measure at depth of 20 cm, waveguides are placed in the soil horizontally at that depth. If 30 cm waveguides are placed vertically into the soil, the moisture content determined by the TDR will be the integrated moisture content from the soil surface to a depth of 30 cm.

The technique is based upon cable testing technology, with a broad-band Electromagnetic step pulse generated and propagated along a coaxial cable (Fig. 1.). At the end of the cable stainless steel rods (waveguides) are inserted into the ground. The time of travel of the EM wave is determined by the apparent dielectric (Ka) of the medium (in this case soil). Water with a high dielectric (Ka = 80), compared to soil (Ka = 3 to 5) and air (Ka = 1), dominates the measured Ka. Thus, if the soil is saturated the Ka is high (due to the presence of increased water) and the travel time of the EM wave along the waveguides is long. If the soil is dry the travel time along the waveguides is short and the Ka is therefore low. Eq. 1. shows the relationship of Ka to travel time (Dt).

Ka = (cDt /2L)2 eq. 1.

Where c is the velocity of light (3 x 108 ms-1) and L is the length of the wave guide (m). Topp et al.7 empirically related Ka to qv via third order polynomial and this equation (eq. 2.) is the basis for soil moisture measurements at present.

Figure 1. Schematic diagram of an electromagnetic wave generated by a step pulse TDR system as it travels along the coaxial cable and down the waveguides into the soil.
qv = -5.3×10-2 + 2.92×10-2Ka – 5.5×10-4Ka2 + 4.3×10-6Ka3 eq. 2.

Further calibration is required for soil high in organic matter and other materials such as grain. In the field waveguides (stainless steel) are of two forms being either balanced (two-wire) or unbalanced (three-wire) as shown in Fig. 2. Generally, two wire probes are used for portable measurement and the three wire probes for permanently placed waveguides.

Effective length of waveguides (and therefore the depth of measurement) will be determined by the power of the step pulse generated by the TDR, the soil type (heavy clay attenuates the wave more so than lighter soil types) and the moisture content of the soil. Waveguides of length 2 m have been successfully used to measure moisture content in Australian soil.9 However, in wet heavy clay soil waveguide length has sometimes been reduced to as little as 30 cm. This current problem is being rectified by increasing the power and stability of the EM wave and by coating waveguides with thin cover of a low dielectric material. This will ensure that a percentage of the wave will travel the length of the waveguides and be reflected allowing determination of ?t. Importantly, the attenuation of the EM wave in conducting soil (soil with a high electrical conductivity) will allow the TDR technique to independently measure moisture content and bulk soil electrical conductivity. This is important for the measurement of solute travel10,11 (e.g. applied fertiliser).

Research is increasing in developing further applications of TDR such as surface measurements, profile measurements, long range multiplexing of waveguides and solute transport determination. This technique will be more widely used in the future by research and irrigation managers.

Figure 2. Schematic diagram illustrating the connection of the coaxial cable (unbalanced signal) to the stainless steel waveguides through, a) a balun for the two-wire system, and b) direct to the waveguides in the three-wire system.

Tensiometers

Portable and stationary tensiometers measure the soil moisture content as a tension or pressure ranging from 0 to -100 kPa, (0 to -1 bar). Tensiometers fundamentally act in a similar fashion to a plant root measuring the force that plants have to exert to obtain moisture from the soil. As the soil dries the water is lost from the tensiometer via a ceramic cup. The loss of water creates a vacuum in the tensiometer and is reported as a pressure reading, the drier the soil the higher the pressure reading, (noting -0.1 bar is considered field capacity and -15 bar wilting point).

Tensiometers may be placed permanently in the soil giving an analogue or digital output. Logging of tensiometers is possible via transducers and a communication cable back to a computer or datalogger. Portable tensiometers allow greater freedom of sampling giving relatively quick readings of soil moisture tension. Tensiometers can take time to equilibrate especially in heavier soil types and this should be accounted for in determining an irrigation scheduling regime. Tensiometers must be installed correctly and well maintained to operate accurately and the practical limit for reliable readings generally -800 kPa (-0.8 bar).

Frequency Domain (Capacitance)

The capacitance technique is similar to that of TDR in that the apparent (Ka) dielectric of the soil is measured and empirically related to the moisture content (qv). A high frequency transistor oscillator (150 Mhz) operates with the soil (dielectric) forming part of an ideal capacitor as shown in eq. 3.

C = Keo A/s eq. 3.

where the dielectric (K) is related to the capacitance (C) via the relationship of the total electrode area (A) and spacing of the electrodes (s), noting that (eo) the permittivity of free space is constant.12

In a field situation the design of the capacitance probe is not ideal with two annular rings (electrodes) placed in a plastic access tube in the soil. The measured area is now removed from between the electrodes to outside the access tube as shown in Fig. 3. Thus, in a field situation the measured capacitance (C) is determined as:

C = gK eq. 4.

where the C is related to K via a geometrical constant (g).13 g depends upon electrode spacing, area and orientation of the electrodes in the soil and eo.12

Measurement is undertaken by either lowering a sensor into the access tube14 or placing an array of sensors into the access tubes and logging the output frequency. The measured (angular) frequency is related to the soil moisture content via a non-linear calibration. Measurement of absolute moisture content is dependant on soil type and bulk density.

The potential for capacitance based soil moisture determination is good13. However, development is required to determine the actual measurement area of the probe and its spatial sensitivity to change in moisture content. Further, the calibration of the technique in situ needs to more fully understood to allow universal use and the effect of electrical conductivity, temperature and acid soil on measured frequency has not been fully studied (T.J. Dean, pers comm.).


Figure 3. Schematic diagram of capacitance probe in an access tube (after White and Zegelin12)

Electrical Resistance (Gypsum)Blocks

Electrodes are embedded in a porous (gypsum) block and placed in the soil at different depths in the root zone. The water in the soil will reach an equilibrium with the water in the gypsum block and the electrical resistance is then determined and related to moisture content as a tension (kPa or bars). Gypsum blocks do not measure the moisture content at low potential (from 0 to -100 kPa) well. The operating range is suited from about -100 kPa to -1500 kPa (as the soil dries). Gypsum blocks will dissolve over a period of time (with the rate of dissolution increasing in sodic soil2) generally lasting for two to three seasons in good conditions.

Large errors, up to 100%, can occur due to: slow equilibrium of blocks with the actual soil potential; the dependence of resistance on the block temperature; effect of hysteresis on calibration of block (if undertaken to improve accuracy) and actual contact with the soil; and, blocked pores by fine material (e.g. silt or clay particles)2,12. Electrical resistance is a useful indicator of the soil moisture content in respect to root conditions such as: plentiful water; good growing conditions; approaching water stress; and water stressed plants.

Conclusions

The need to determine the moisture status of the soil is a critical factor influencing plant production. Correct irrigation scheduling can control the soil moisture status reducing through-drainage and maintaining optimum levels of soil water for maximum plant growth. To implement a reliable and accurate irrigation scheduling regime regular, objective soil moisture readings are essential. There are different tools available for obtaining soil moisture content including NP, TDR, tension and capacitance techniques. The choice of instrumentation will be determined by the form of information required by the operator, the soil type, relative cost, reliability and ease of use in the field.

Acknowledgements

The author wishes to acknowledge the Department of Industry, Technology and Regional Development for support through the National Teaching Company Scheme (agreement number 12234).

Testing Moisture In Plants: How To Gauge Soil Moisture In Plants

Adequate moisture is critical for growing plants successfully. For most plants, too much water is more dangerous than not enough. The key is to learn how to gauge soil moisture effectively and to water plants only when they need it, not on a set schedule.

Checking Plant Moisture

When it comes to testing moisture in plants, the feel of the soil is the best guide. As a general rule, a potted plant in a container measuring 6 inches (15 cm.) in diameter needs water when the top 2 inches (5 cm.) of soil feels dry to the touch. A larger container measuring 8 to 10 inches (20-25 cm.) in diameter is ready for water when the top ½ to 1 inch (1.25-2.5 cm.) of soil feels dry.

Insert a trowel into the soil, then tilt the trowel to check the moisture of garden plants. You can also insert a wooden dowel into the soil to determine the depth of soil moisture. If the dowel comes out clean, the soil is dry. Damp soil will cling to the dowel.

In most cases, the soil should be damp to the root zone – 6 to 12 inches (15-30 cm.). However, sandy soil drains quickly and should be watered when the soil is dry to a depth of 2 to 4 inches (5-10 cm.).

Remember that the need for water also varies widely depending on the plant. For example, most succulents require dry soil and infrequent watering while some plants, such as columbine, prefer consistently moist soil. However, nearly all plants require air circulation around the roots and are prone to rot in poorly drained, waterlogged soil.

Soil Moisture Tools

Soil moisture monitoring can also be achieved with specific tools. A variety of simple, inexpensive soil moisture meters are available in garden centers and nurseries, and many are suitable for both indoor and outdoor growing. The meters, which tell you if the soil is wet, moist, or dry at the root level, are especially effective for large potted plants.

Other soil moisture monitoring tools, often used for agricultural applications, include tensiometers and electrical resistance blocks, which indicate the moisture tension of the soil. Although both are accurate and easy to operate, they are more expensive than simple probes.

Time Domain Reflectometry (TDR) is a newer, more expensive method that measures soil moisture quickly and accurately. However, the sensor often requires recalibration and the data tends to be relatively difficult to interpret.

Best Soil Moisture Meters 2020 – Reviews & Buyer’s Guide

Last Updated: January 8, 2020

Measuring the moisture levels of soil isn’t exactly exciting work, but for a surprising chunk of the population, it is important. You don’t have to be a farmer to need a soil moisture meter. Gardeners, scientists, and a variety of other professionals may regularly need to use one of these tools.

Not only do they need one, but they also need a good one. Moisture meters are precision tools. If yours isn’t giving the most accurate reading possible, there really isn’t any point in having it.

The problem is that unless your moisture meter starts giving you radically bizarre numbers, it can be hard to identify if one is inaccurate.

The best way to ensure you get accurate readings is to buy a solid product from the get-go. But then you bump into another problem. Namely, how can you know if a moisture meter is reliable if you haven’t used it before?

The answer? By reading a guide like this one.

We’ve studied the market and put together these soil moisture meters reviews to help you make your decision. Read on!

Comparison of our Favorite Products:

Model Price Warranty Editor Rating
Gain Express Soil Ph & Moisture Meter 295mm
(Top Pick)
Check Price 4.7/5
VIVOSUN Soil Tester, 3-in-1 Plant Moisture Meter
(Best for the Money)
Check Price 4.5/5
Sonkir Soil pH Meter Check Price 1 Year 4.3/5
XLUX T10 Soil Moisture Sensor Meter Check Price 1.5 Years 4.2/5
Jellas Soil Moisture Meter – 3 in 1 Soil Tester Kit Check Price 1 Year 3.9/5

5 Best Soil Moisture Meters – Reviews 2020:

1. Gain Express Ph & Soil Moisture Meter 295mm – Top Pick

This Gain Express Soil pH moisture meter takes the cake. It produces high-quality results in a variety of applications.

One of the first things that drew us in with this option is that it’s incredibly simple to use. There is no setup—it doesn’t even require batteries. Simply introduce the needle into the soil, and let the product do what it was made for.

We also appreciate the quality of the unit itself. Its easy-to-read meter allows you to detect pH levels in the soil at a range of 3-8. And it also detects moisture.

Of course, like any product, it also has its share of flaws. The big issue we noticed here was that, while the results themselves are reliable, they take a significant amount of time to appear. Digital moisture meters sometimes give results instantaneously; this unit keeps you waiting for a while.

That said, many buyers may appreciate the simplicity of the unit enough to make the compromise.

Pros

  • Easy to Use
  • Easy to read interface
  • Reads for pH between 3-8

Cons

  • Slow to produce results

2. VIVOSUN Soil Tester, 3-in-1 Plant Soil Moisture Meter – Best for the Money

The Vivosun Soil Tester has the distinction of being both our runner-up and our “best for the money.” Not only did we find it to be the second best option we encountered, but we also recognized that it possesses a great combination of quality and value.

One of the things we appreciate about this unit is its versatility. In addition to reading moisture, it’s also able to detect pH levels and determine how much sunlight a particular spot is getting.

The readable scales are also very easy to understand. PH is measured at a range of 3.5-8. Sunlight is measured at a range of 0-2,000 (going from low to high), and moisture is measured at a range of 1-10.

It’s also durable, portable, and of course, very affordable.

That said, not everything about this handy tool is rosy.

For one thing, like our first pick, this unit can take quite a bit of time to respond. We also found that it’s very fragile, which means it may not stand up so well to the harsh outdoor climate.

Deal breakers? For some, maybe. However, others may find that the bargain is good enough to overlook these drawbacks.

Pros

  • Best for the Money
  • Easy to Use
  • Three in One Application

Cons

  • Fragile
  • Slow to Respond

3. Sonkir pH Soil Moisture Meter

With the Sonkir, we have an option that looks almost identical to our runner-up. It tests for sunlight, pH, and moisture. It’s affordable, and it’s also very easy to use, requiring no batteries to get started. It even features two reading needles rather than one which might (potentially) increase the accuracy of the readings.

So, why didn’t this unit find itself in our top two? While this reader is quite similar to our “best for the money” pick, there are a few reasons we feel it isn’t quite as good.

For one thing, the Sonkir seems very flimsy. The prongs bend a little bit as you insert them into the soil. Over time, they may become completely unusable.

There’s also a concern with accuracy. The unit we used actually worked fine, and that seems to be the general consensus among other users as well. However, some people appear to have a difficult time getting accurate readings on all three of the things that the reader is supposed to test for.

This is a defect, rather than something that all users will encounter. Even so, it’s not encouraging to see.

Still, if you want an affordable moisture meter, and weren’t blown away by our runner-up, this might be a good alternative.

Pros

  • Affordable
  • Three in One
  • Easy to Use

Cons

  • Very Flimsy
  • Some people experience trouble with accuracy of readings

4. XLUX T10 Moisture Meter for Soil & Plants

For our penultimate listing, we have the XLUX T10 Soil Moisture Sensor Meter. This is probably the simplest option on our list, which incidentally, is part of the reason it landed second to last in the rankings.

This tool will only test for moisture, which is fine if that’s all that you need. However, having pH and sunlight readings can provide additional helpful data.

Like most of the options on this list, this unit is also easy to use and affordable.

Our major concern with this instrument, however, is its accuracy problem. The unit measures on a scale of 1-10, but seems to register virtually all soil, regardless of how wet the ground is.

In other words, you aren’t getting the best information available with this tool. We also found that it’s somewhat fragile.

For the money, most buyers will probably prefer something that is more accurate.

Pros

  • Affordable
  • Easy to Use

Cons

  • Fragile
  • Not very accurate

5. Jellas Soil Moisture-Meter – 3-in-1 Plant Tester Kit

Finally, we have the Jellas Soil Moisture Meter. You’ll find a lot of familiar features here. It offers a three in one reading (sunlight, pH, and of course, moisture) and an easy-to-use interface.

So, why did the Jellas come in dead last? There are a lot of reasons, but they can all be summed up in one word: reliability. The prongs on this unit are not at all durable. This is obviously a problem because the prongs are the most important part of any moisture meter. We also found that they corrode very easily.

And again, we have the problem of accuracy. The meter will give readings for moisture or sunlight that clearly contradict your own observations. Calling wet soil dry, for example.

If you need a moisture meter that’s extremely cheap, this might be the one for you. However, your money will probably be better spent on our “best for the money” pick.

Pros

  • Three in One
  • Easy to Use

Cons

  • Inaccurate
  • Prongs Corrode Easily

Buyer’s Guide

If the reviews above left you with some questions, that’s ok. We’ll attempt to answer some of them now with our buyer’s guide on moisture meters. Read on!

Batteries?

None of the units today require batteries to operate. There are pros and cons to going with battery-operated units. On the one hand, they’re pricier to buy and maintain. On the other hand, they’re usually more responsive and give quick results.

If you’re a gardener on the go, you may find value in a battery-operated unit. Just be prepared to pay more for the convenience.

Features

You probably noticed that virtually all of our choices on this list measure more than moisture. Some also check for pH and sunlight.

Consider what sort of features you need going in. Most people who need to measure moisture may also find it handy to know the levels of pH in their soil, as it is a critical component of agriculture and gardening.

Ease Of Use

As data recording instruments, there’s a scientific element to moisture meters. However, they don’t have to be inaccessible.

If you don’t have a master’s in agricultural science, you’re probably going to want to go with an instrument that doesn’t require a graduate degree to understand.

Fortunately, all of the options in this list distill information into very easy-to-read measurements.

Price

Last but not least, we have the consideration of price. Soil moisture meters can run less than $10, or well over $100. Naturally, the difference in quality will more or less correspond with the differences in price.

You don’t have to break the bank to get a decent option here. Our “best for the money pick,” for instance, gives good readings at an affordable price.

However, if you’re buying this tool for professional purposes, you may find it worthwhile to spend more money.

When your livelihood depends on an accurate understanding of moisture and pH levels, you want to arm yourself with the best tools you can get.

We also have a buyer’s guide for wood moisture meters found here. <–

Conclusion

Now that you’ve read our soil moisture meter reviews it’s time to pick an option that will be right for you.

While choosing can be hard, we do have two recommendations for you that might simplify the decision a little bit.

If you value quality over everything else (including price), you’ll probably appreciate the Gain Express Soil Ph & Moisture Meter.

But if you have to factor the budget into your decision, you may be more comfortable with our “best for the money” pick, the VIVOSUN Soil Tester.

At the end of the day, it’s all about finding the product that is right for your needs. The good news is that after reading this guide, you are now armed with enough information to confidently make that decision for yourself.

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