How to measure soil?

Measuring Soil Water

There are several ways of estimating soil moisture from the simplest and subjective to advanced technology. A compromise between practicality and accuracy needs to be made. How close to actual field capacity is needed? For most situation in scheduling irrigation in potato fields, an accuracy of 5% is acceptable. The keys are how much water is in the soil and where in the soil profile, in other words, the depth of water penetration from irrigation and rain. Soil texture or the relative amounts of sand, silt and clay in the soil are the critical factors influencing the amount of available water to the plant (Table 1).

Table 1: Available water capacity of soils

(Modified from Klocke and Fischbach, 1984, and Kranz et al., 1989)

Below is outlined three common methods for estimating soil moisture during the season: “appearance and feel,” tensiometer and moisture blocks.

1. Appearance and feel (Klocke and Fischbach, 1984).

Different soil types respond in different appearance and feel using this method so it is necessary to know the soil texture. This can be identified from county soil maps at Cooperative Extension offices.

A soil sample needs to be extracted from the potato root zone using either a soil probe for up to 24 inches (bottom of root zone), a soil auger or, at minimum, hand-dug to the depth around the growing tubers. Using the appearance and feel method requires some experience and observation. When first learning it, start using it in the spring after a heavy rainfall when the soil should be saturated (field capacity, FC) and take samples every so often as the field dries until it is quite dry. Record your observations per field for reference. Table 2 lists the appearance and feel that represent different field capacity ranges for various soils. Representative pictures are shown in the NebGuide.

2. Tensiometer (Kranz et al., 1989).

Tensiometers are a common and simple objective way to monitor available soil water. It measures the force that a potato root needs to overcome to absorb water from the soil, and consists of a tube with a porous ceramic tip at the bottom, a vacuum gauge near the top and a scaling cup. The tube is filled with water before inserting it into the soil. Upon insertion of the tensiometer, water can move between the tube and the soil through the ceramic tip. During the drying of the surrounding soil, water leaves the tube creating a vacuum measured by the gauge, calibrated in negative centibars (cb), until an equilibium is reached. The final gauge reading is reached when water no longer flows out of the tube and measures the actual force required to remove water from the soil at that time and location. Therefore, suction pressure is actually measured. The wetter the soil :: the lower the value (less cb needed to remove water; and visa versa. Plants extract water easier from sandier soils than heavier ones due to the larger air spaces in sandy soils. But, note that sandier soils also hold less water.

For an outline on preparation, procedures and data interpretation of tensiometer use, refer to Kranz et al., 1989.

3. Moisture Block (Kranz and Eisenhauer, 1989).

For fine-textured soils such as loam and silt loam, a moisture block is recommended by UNL for measuring soil moisture; they are not recommended for sandy soils because of the large soil particles of these soils. The moisture block is made up of gypsum and is about an inch in size. The gypsum is attached via a wire to a measuring meter. Being measured is the electrical resistance between two wires imbedded into the gypsum block. Water from the soil enters the block saturating the gypsum. Electrical resistance through the gypsum decreases allowing more electrical flow between the two imbedded wires. This electrical flow is measured by the meter. A high reading indicates a moist soil while a low one indicates a dry soil. For details on preparation and use of moisture blocks, refer to Kranz and Eisenhauer, 1989).

Measuring Soil Water Content: A Review

Physical principles

Soil water content can be measured directly or indirectly. In the first case, the amount of water is directly measured, for instance, by measuring its weight as a fraction of the total soil weight (gravimetric method). However, this measurement method usually is destructive since the soil sample is removed from the field to be analyzed in the laboratory. Moreover, it is a time-consuming and impractical way of measuring SWC in the field. Because of these limitations, a variety of indirect measurements (also called surrogate methods) have been developed.

An indirect method measures another variable that is affected by the amount of soil water, and then it relates the changes of this variable to the changes in SWC, through physically based or empirical relationships called calibration curves. For instance, the dielectric sensors exploit the changes in soil dielectric properties as function of SWC; the heat dissipation and heat flux sensors use the changes in the soil thermal properties; the neutron scattering technique is based on the loss of high-energy neutrons as they collide with other atoms, in particular hydrogen contained in the water molecule. Although the direct gravimetric method is the reference method for SWC measurement (and commonly used for indirect methods calibration), the majority of the commercial sensors are based on indirect methods. Specific descriptions are provided below.

  1. a) Thermogravimetric measurement is a direct method, and it is the reference method for SWC measurement. It is based on the weight measurement of a wet sample before and after oven drying at 105 °C for 24 h (Evett et al., 2008). The difference in weight is expressed as fraction of the soil solid weight (ms), called gravimetric water content (). This quantity can be expressed as volume fraction, by multiplying the gravimetric water content by the bulk density of the sample and dividing by the density of liquid water, , where and are the soil bulk and water density, respectively. The value of bulk density should be obtained by volumetric and weight measurements of the same sample, which are then used to determine the gravimetric water content. Using bulk density values obtained from tables or from previous measurements should be avoided since SWC and bulk density are properties that vary in space and time. Both error (bias) and imprecision (larger variance) occur when volumetric water content is calculated using an assumed bulk density or one measured elsewhere or at another time (Evett et al., 2008). When the thermogravimetric measurement is performed for calibration of other SWC sensors, it is important to measure the sample bulk density for conversion into the volumetric form since many indirect methods (e.g., the dielectric sensors) provide volumetric measurements of SWC.
  2. b) Dielectric measurement takes advantage of the differences in dielectric permittivity values between different soil phases (solid, liquid, and gas). Liquid water has a dielectric permittivity of ≈80 (depending on temperature, electrolyte solution, and frequency), air has a dielectric permittivity of ≈1, and the solid phase of 4 to 16 (Hallikainen et al., 1985; Wraith and Or, 1999). This contrast makes the dielectric permittivity of soil very sensitive to variation in SWC. The measurement of the bulk dielectric permittivity is then used to obtain the volumetric water content through calibration curves (Roth et al., 1990; Topp et al., 1980).

Although many different electronic devices and experimental techniques are available, all the dielectric sensors exploit the effect of liquid water dielectric permittivity on the bulk soil dielectric properties. Some sensors derive the dielectric permittivity by measuring the travel time of an electromagnetic wave traveling back and forth on the probe, such as time-domain reflectometry (TDR; Robinson et al., 2003), or by measuring the capacitance of the bulk soil. Other sensors measure the dielectric properties of the reflected electromagnetic wave in the frequency domain, to obtain the dielectric properties of the bulk soil. Indeed, important families of sensors used for SWC are the frequency-domain reflectometry and the capacitance sensors, also referred as dielectric sensors or electromagnetic sensors (Evett and Parkin, 2005; Gardner et al., 1998; Robinson et al., 1999, 2003). These sensors measure the dielectric permittivity of the media using capacitance/frequency-domain technology. Some devices are also equipped to measure SWC, soil temperature, and soil electrical conductivity (EC) within the same sensor.

The accurate use of these sensors requires a good understanding of several factors affecting the measurement, such as the geometric properties of the sensors, soil temperature, bulk soil EC, and the electronic features of the different sensors (Bogena et al., 2007; Robinson et al., 2003). Some authors analyzed different dielectric sensors to review their performance and compared them (Blonquist et al., 2005; Evett et al., 2008, 2009). Soil dielectric properties are also used as a basis for measurements of earth soil moisture using ground-penetrating radar (GPR) for measurement of SWC at larger scales (Gerhards et al., 2008; Huisman et al., 2003).

  1. c) Resistivity measurement is based on the principle that soil resistivity is affected by SWC. Usually, a current is transferred into the soil by electrodes, and the value of soil resistivity is then obtained by measuring the changes in voltage. The most common approach is to use four-probe resistance methods such as the typical Wenner array (Wenner, 1915) or other configurations that allow for insertion of multiple electrodes into the soil to obtain soil tomography (Amer et al., 1994; Samouelian et al., 2005; Seyfried, 1993). Other new technologies include the automatic resistivity profiling system, where the electrodes are the wheels of a machine pulled on the soil, which allows for rapid tomography of large areas (Dabas, 2006, 2009). Additional resistivity methods are also available, such as the OhmMapper system (Geometrics, San Jose, CA), which uses electrodes that are dragged on the soil surface (Walker and Houser, 2002).
  2. d) Neutron scattering technique also called neutron probe employs high-energy neutrons produced by a radiation source, which collide with soil atoms. Fast neutrons are emitted by a radioactive source. The neutrons lose their energy as they collide with other atoms, in particular hydrogen. Therefore, the neutrons are slowed down and counted. The instrument is equipped with a source of fast neutrons and a detector of slow neutrons. The number of hydrogen atoms in soils changes because of the change in SWC; therefore, the hydrogen content can be calibrated vs. the count of slow neutrons (Hignett and Evett, 2002). According to Evett (2008) a field-calibrated neutron moisture meter is the most accurate and precise indirect method for SWC measurement in the field. These sensors can be placed on the soil surface or as inserted tube for the measurement of the SWC profile.
  3. e) Measurement of soil thermal properties is an indirect method that exploits changes in soil thermal properties due to variation of SWC. The two main techniques are heat dissipation and heat pulse. The heat dissipation technique uses a heat source (usually a heated needle) and temperature sensors (thermocouples or thermistors), immersed into a porous ceramic that equilibrates with the surrounding soil at a given water content. The needle is heated, and the rate of heat dissipation is measured by the temperature sensors. These changes are affected by the thermal conductivity, which depends on the ceramic water content. The thermal conductivity is then obtained through measuring the differential temperature before and after heating (Shiozawa and Campbell, 1990; Young et al., 2008). In the heat flux method, the pulse of heat is applied at one location and its arrival at another location is determined by measuring the soil temperature at the other location. The time required for the pulse of heat to travel to the second location is a function of soil thermal conductivity, which is related to water content. The heat dissipation sensors are also used to estimate soil water potential, through calibration of the sensors at specific soil water potentials (Reece, 1996).

Although the techniques described above are the most common ones, other techniques are also developing such as acoustic wave methods (Adamo et al., 2004; Blum et al., 2004; Lu, 2007), optical methods (Selker et al., 2005; Tidwell and Glass, 1994) and gravity measurements (Leiriao et al., 2009).

how to convert gravimetric soil water content to volumetric soil water content

The amount of water or moisture in soil can be measured as either gravimetric soil water content (GWC) or volumetric soil water content (VWC).

But what is GWC and VWC? And how do you convert GWC to/from VWC?

  • The Soil Water Compendium
  • 5 Common Mistakes When Measuring Soil Moisture
  • How to Calibrate Soil Moisture Sensors

The easiest way to think of GWC and VWC is that GWC is related to the mass of water and soil, whereas VWC is related to the volume of water and soil.

GWC is the mass of water per mass of dry soil in a given sample. To determine GWC, collect soil sample from the field, weigh that soil then dry it in the oven at 105°C for at least 3 days (or, more precisely, weigh the soil periodically until there is no more loss in weight which indicates that all of the water has been dried from the sample). The equation for GWC (θg) is:

θg = (Wet – Dry) / Dry (Equation 1)

where Wet is the weight of the soil sample from the field and Dry is the weight of the dry soil sample.

VWC is the volume of water per volume of soil. To determine VWC, you will need to measure Wet and Dry as described above for GWC. You will also need to know the bulk density of the soil sample (BD).

In this case, it is not enough just to collect a handful of soil sample from the field. It is better practice to collect a sample of soil in a known volume, such as a metal cylinder. The BD is the ratio of Dry to the volume of your sampler. (A You Tube video at the bottom of this article outlines how to collect soil samples to measure soil bulk density.) The equation for VWC (θv) is then given by:

θv = θg * BD (Equation 2)

Soil scientists also incorporate the density of water (WD) into θv as:

θv = θg * (BD / WD) (Equation 3)

However, the value of WD is close to 1 and is typically ignored when calculating θv.

In summary, Equation 1 is used to calculate gravimetric soil water content and Equation 2 is used to calculate volumetric soil water content.

related equipment
  • Soil moisture sensors, meters and data loggers
  • Soil water potential sensors and meters
  • Soil water research equipment
how to measure soil bulk density

We’ve looked at how water is held in the soil and why it’s important to know how much water is there. Now we consider how to measure the quantity of water in the soil.

Firstly we need to address how to quantify the soil moisture content; there are two ways to do this, by mass or by volume.

If a sample of soil has a total mass equal to mt, this has two component parts the mass of the soil (ms) and the mass of the water contined in it (mw) – clearly mt=ms+mw. The water content can be expressed as a fraction of the soil dry weight, i.e., mw/ms. This is a dimensionless quantity known as the gravitational water content, and normally represented by Θm (Greek capital letter theta with subscript m for mass).

The volumetric water content is a similar ratio but is expressed as vw/vt, where vw is the volume of water, and vt is the total volume of the soil sample. In this case vt=vs+vw+vg, where vs is the volume of soil and vg is the volume of gas (air) in the soil. The gas has neglible mass and could be ingnored when expressing the water content by mass, but the volume of gas, i.e. all of the pore space that exists between the soil grains, is significant and must be acknowledged. The volumetric water content is usually represented by Θ.

These various masses and volumes can be used to give other soil properties such as bulk density (ρb=ms/vt – that’s lower case Greek letter rho with subscript b) and porosity (f={vw+vg}/vt).

Measurement techniques

The gravitational water content, Θm, is found by weighing a sample of the soil to obtain mt, drying the soil to remove the moisture and reweighing to determine ms; mw is mt-ms. The drying should be at 105 deg C and be for long enough to remove all of the water, i.e. further drying doesn’t give a different value for ms. Note that this is not hot enough to remove the tightly bound (hygroscopic) water which gets included within ms, but this is small compared to the other components. Heating at higher temperatures will burn off organic compounds in the soil, which should be included as the mass of the soil, ms, and not added to the mass of the water, mw.

The volumetric water content is obtained by the same process except that the sample taken is of a specific, known, volume. Because it’s a known volume, the bulk density, ρb, of the sample can be calculated and the volumetric water content, Θ, is Θmρb/ρw, where ρw is the density of water which is a known constant (1 kg/l or 1 g/cubic cm).

The requirement to dry the soil sample means that a sample must be obtained from the field and returned to a laboratory for analysis, a procedure that is destructive (soil is physically removed) and time consuming for every measurement of soil moisture required. For these reasons several alternative methods have been developed that are non-destructive, require less effort and may be automated. These are all indirect methods in which some property of soil is measured and then converted to a moisture content. As such they require calibration to ensure an accurate conversion between the instrument’s output and soil moisture content.

The first of these methods, the tensiometer, measures the pressure in the soil caused by the surface tension (suction) forces described earlier. Traditionally this pressure was read using a manometer but there are electronic sensors that can be used to automate measurement. The pressure is related to water content by a soil retention curve, which varies with soil type and usually exhibits hysteresis, i.e. different curves describe the wetting-up and drying-out of soils. These are inexpensive instruments and are routinely used for informing farmers of the need for irrigation.

Gypsum, or electrical resistance, blocks work on the principle that water in the soil lowers its electrical resistivity. The material from which the block is made is such that it is well connected with the moisture regime in the surrounding soil so that water content and pore pressure is the same in the block as in the soil. Probes embedded in the block allow the resistivity to be measured, again without the need for an operator. As with tensiometers the method requires calibration for the particular soil, and will be subject to hysteresis.

Two other techniques, time domain reflectometry (TDR) and time domain transmissometry (TDT), are also based on the changes in (dielectric) soil properties that can be measured using electromagnetic pulses. These methods are accurate, fast, non-destructive, capable of automated operation, and can be used without site-specific calibration.

Another measurement technique is based on neutron scattering. A source of fast neutrons is lowered into an access tube in the soil. The neutrons collide with hydrogen nucleii in the soil and are converted to slow (thermalized) neutrons that are reflected and monitored by a counter. The source and counter are normally mounted in a single probe that can be operated at different depths to monitor variations in soil moisture within the soil profile. The volumetric water content is derived from the count ratio that compares the number of counts with a background reading from a reference medium. Neutron scattering methods have become less widely used as other methods were developed mainly because of issues associated with operating radiation-emitting devices.

All of the technologies discussed above provide a measure of soil moisture in a very small volume of soil, they can be very labour intensive and require many such measures to describe the moisture content across a field. What has been lacking is a measurement technique that works at the field or landscape scale. Two techniques are able to provide landscape-scale assessments of soil moisture. One of these is the cosmic-ray based soil sensor (CRS), the other is remote measurement from satellites. Satellites have the potential to provide repeat observations at a global scale but still require calibration from ground-based sensors. Satellite methods are not described further here.

The cosmic ray soil moisture sensor (CRS)

The CRS sensor works in a similar way to the neutron probe with the big difference that it uses cosmic rays as the source of fast neutrons, thus avoiding the problems of handling a radioactive source.

A large benefit of this method is that a CRS integrates soil moisture over an area up to 400m in diameter, and to a depth of up to 70 cm; in fact these figures for area and depth are likely maxima, and decrease with water content so that in a wet soil the effective depth may be as low as 15cm. A further benefit of the CRS is that it sits above the ground and can operate remotely with little maintenance.

Obtaining soil moisture information from the CRS requires many adjustments to the monitored counts of slow neutrons to correct for variations in in-coming cosmic-rays, atmospheric pressure, humidity and altitude. In practice calibration against volumetric soil moisture derived from multiple samples within the measurement area is also needed.

In summary, there are many measurement techniques which mainly use indirect methods. Their varied characteristics mean that different techniques are suited to different applications.

The COSMOS-UK network is based on the CRS to give the landscape-scale picture but is backed up by point measurements based on dielectric soil properties.

Understanding how these different methods can best be used to provide UK-wide real-time information is the subject of on-going scientific research.

Previous: Why measure soil moisture?

Soil Calculator

Dirt calculator – how to estimate garden soil quantity?

Let’s deal with a real-life situation. Imagine that you have just built your beautiful house, with a roof finished with warm red tiles. You want to surround it with a grass yard and pavement made of tiles. To calculate the number of tiles and the amount of paver sand you need to buy before getting to work we recommend you visit our tile and paver sand calculators. It would be a shame to buy too much or even worse – not enough materials, and have to go back to the home improvement store.

Now, let’s get to the grass yard. We want to calculate the required quantity and cost of garden soil. As you can see, we cannot just type the width and length into our dirt calculator as there is a pool in the middle of it. How to deal with this problem?

  1. First, we need to divide the grass yard into four rectangles: 1, 2, 3, and 4.
  2. Now, we have to measure the width and length of each sector:
  • Sector 1 has the width of 2 yd and the length of 25 yd;
  • Sector 2 has the width of 3 yd and the length of 2 yd;
  • Sector 3 has the width of 3 yd and the length of 10 yd;
  • Sector 4 has the width of 2.7 yd and the length of 25 yd.
  1. Let’s calculate the area of each rectangle:
  • Sector 1: the area is equal to 2 yd multiplied by 25 yd, which gives 50 yd²;
  • Sector 2: the area is equal to 3 yd multiplied by 2 yd, which gives 6 yd²;
  • Sector 3: the area is equal to 3 yd multiplied by 10 yd, which gives 30 yd²;
  • Sector 4: the area is equal to 2.7 yd multiplied by 25 yd, which gives 67.5 yd².
  1. We have to sum up these four different areas to get the area of the whole yard.

    50 yd² + 6 yd² + 30 yd² + 67.5 yd² = 153.5 yd²

    You can already jump to the third point of topsoil calculator instruction in How much soil do I need? paragraph.

  2. It is time to choose the desired thickness (depth) of the topsoil level. Let’s make it 0.6 yd. We want to create enough space for the roots of grass to grow freely and without any obstacles. Furthermore, a thicker layer of topsoil will be able to absorb more water and hold the moisture for a longer period.

  3. You can calculate the required volume of soil by multiplying the grass yard area by the desired thickness of soil.

    153.5 yd² * 0.6 yd = 92.1 yd³

  4. The last thing to do is to assess the estimated weight of the required soil and its cost. The weight of the cargo may come in handy when transporting the soil. It would be nice to know that your truck or trailer will endure the burden of your purchase. As we have already mentioned, you should find the density of the chosen soil on its package. You just need to multiply it by the volume of our topsoil layer. And last but not least – money. Can you afford such an expense? Maybe we could save some money by reducing the thickness? To know that, you need to calculate the total cost. With our soil calculator, you can do it by multiplying the volume of purchased soil or its weight by the price of one cubic yard or price of one ton (other units of weight or volume are also available).

Oh, and if you were wondering whether we can also help you with finishing your interiors, yes, you’re right – we’ve got calculators for that as well! You can organize the space with drywalls and then paint the rooms using our drywall and paint calculators. Now, there is nothing left to do apart from relaxing in the cool water and inviting your friends for a barbecue!

4. Soil Organisms

Measure the animal life in your soil by digging down at least 6 inches and peering intently into the hole for four minutes. Tick off the number and species of each organism observed, such as centipedes, ground beetles, and spiders. Because most soil organisms spurn daylight, gently probe the soil to unearth the more shy residents. If you count less than 10, your soil does not have enough active players in the food chain.

Why It’s Important

A thriving population of diverse fungi, bacteria, insects, and invertebrates is one of the most visible signs of soil quality. The more that creeps and crawls under your garden, the less opportunity there is for unwelcome pests and disease. Each level of soil life does its part to break down plant residue and make more nutrients available for growth.

5. Earthworms

When the soil is not too dry or wet, examine the soil surface for earthworm castings and burrows. Then dig out 6 inches of soil and count the number of earthworms squirming on the shovel. Three worms are good; five are better. The absence of worms means the soil does not have enough of the organic matter they feed on. An exception: If you live in the Southwest, don’t waste your time looking even if the soil displays other signs of good quality. “Earthworm activity is less likely in the desert,” says Walworth. “Worms don’t like hot soil.”

Getty Images

Why It’s Important

Not only do earthworms aerate the soil, but their castings infuse the soil with enzymes, bacteria, organic matter, and plant nutrients. They also increase water infiltration and secrete compounds that bind soil particles together for better tilth.

6. Plant Residue

If you’ve grown a cover crop, dig down 6 inches one month after turning it into the soil and then look for plant matter. The range of organic material is important to notice here. The presence of recognizable plant parts as well as plant fibers and darkly colored humus indicates an ideal rate of decomposition.

Why It’s Important

“The single most important component of healthy soil is organic matter,” Thompson says. But plants and other organic materials decompose only when soil organisms are there to do the work. Any sign of this process is a good sign, but the speed of decomposition is important, too. Fast decomposition is another indicator of soil quality. In poorly aerated soil, plants break down slowly, a condition that gives off a faintly sour scent.

7. Plant Vigor

Start this test during the active growing season and look for healthy plant color and size that’s relatively uniform. Overall health and development must be judged against what’s considered normal for your region. One caveat: If you suffered a pest infestation or planted late or during a drought, results of this test may be unreliable.

Why It’s Important

Plant vigor indicates soil with good structure and tilth, a well-regulated water supply, and a diverse population of organisms. It’s the best sign of effective soil management you’ll have above ground.

8. Root Development

Use a shovel or hand trowel to dig gently around a selected plant, preferably a weed you won’t miss. Once you’ve reached root depth, pull an annual plant up and check the extent of root development, searching for fine strands with a white healthy appearance. Brown, mushy roots indicate serious drainage problems — and a poor outlook for this year’s harvest. Stunted roots might also indicate disease or the presence of root-gnawing pests. “When you look at the roots, you can really see what’s going on,” Allmaras says.

Getty Images

Why It’s Important

Roots have the most immediate connection with and reliance on soil quality. Without air, water, biological activity, and crumbly soil to grow in, roots can’t do their job.

9. Water Infiltration

Take an empty coffee can with the bottom removed and push it into the soil until just 3 inches remain above the surface. Fill the can with water, marking the water height and how long it takes for the water to be absorbed into the soil. Repeat this several times until the rate of absorption slows and your times become consistent. Anything slower than 1/2 to 1 inch per hour is an indication of compacted soil.

Why It’s Important

Good infiltration gets water to plants where they need it (at their roots), prevents runoff and erosion, and lets air move more efficiently into soil pores.

10. Water Availability

Wait for a soaking rain; then record how long until plants start to show signs of thirst. Results will vary widely by region. The basic lesson is that if plants require more frequent watering than typical for your region, your soil is probably the culprit.

Why It’s Important

Porous soil can better resist evaporation and adequately supply plants between waterings. “It could make all the difference in the world if water were to go another inch deeper,” Allmaras says.

The Willamette Valley Soil Quality Card Guide, on which this article is based, provides you with even more information and guidance on evaluating your soil and how to improve it based on the results of this test. Get a copy from the Oregon State University Extension Service.

Learn Two Homemade Soil Ph Testing Methods

I’m always looking for quick tips to make my gardening chores easier. I ran across a couple of gardening hacks about testing your soil pH without a kit and I thought I would try them out and see what I need to do with my garden. Let’s do a little kitchen chemistry!

But first…

Why Do You Care if Your Soil Is Alkaline or Acidic?

Knowing your soil pH is the key to understanding if essential minerals will be available to the roots of your plants. You will also know which soil “amendments” are best for your garden. What’s more, you will be able to determine if all the hard work you put in your yard or garden pays off.

For instance, nutrients will have a hard time dissolving in water and reaching plants’ root systems if the soil is too acidic or too alkaline. So, a quick amendment to achieve the best soil pH for your plants and seeds to thrive can be added just in time.

Plus, fungi are less likely to affects your plants if the soil is alkaline and dry enough (below pH 4.5, expect plenty of fungal issues). Soil is too acidic under pH 7 and too alkaline above pH 7. Most plants thrive in a slightly acidic soil (pH 5.5 to 7) so reaching a balance is of the essence in gardening matters too.

So, testing your garden’s soil pH is critical for the well-being of your plants in the long run. You’ll need to consider not only soil pH, but soil texture as well (a no-fuss DIY method to determining the soil’s texture is the “mason jar test.”). But soil pH is the critical indicator of the health status of a garden.

Longing for a simpler life? The Back to Basics Living Summit has FREE presentations from over 25 experts on all aspects of gardening, food storage, and self-reliance. See if it’s for you!

The pH of your soil will determine which plants grow better in your garden and which ones will struggle (without amendments).

According to The San Francisco Chronicle,

if you live in an area with alkaline soil — which has a pH above 7.0 — you have two options. You can either take measures to lower the pH, or you can choose plants well-suited to growing in alkaline conditions. If you take the latter path, you have a wide variety of plants to choose from.”

Want FREE tips and Tricks? Want NEW products to test?

The pH Scale courtesy of

You can lower the alkalinity of your soil by adding organic materials like pine needles, peat moss, and composted leaves. You should always make small changes, over time -so make your soil amendments and wait for it to work before making any more.

According to the article, Your Garden’s Soil, in Mother Earth News, “Raising the organic matter content of soil will usually move the pH of both acidic and alkaline soils toward the neutral range. This is because organic matter plays a buffering role, protecting soil from becoming overly acidic or alkaline. Finished compost usually has a near-neutral pH, so regular infusions of compost should be the primary method you use to improve the soil with extreme pH issues. If your pH readings are only slightly acidic or slightly alkaline, compost and organic mulches may be the only amendments you need to keep your crops happy and your garden growing well.”

#1 – You Can Test Your Garden Soil pH with Vinegar and Baking Soda

Fortunately, you can test your garden soil ph without a soil test kit for a fraction of the price. Collect 1 cup of soil from different parts of your garden and put 2 spoonfuls into separate containers. Add 1/2 cup of vinegar to the soil. If it fizzes, you have alkaline soil, with a pH between 7 and 8.

If it doesn’t fizz after doing the vinegar test, then add distilled water to the other container until 2 teaspoons of soil are muddy. Add 1/2 cup baking soda. If it fizzes you have acidic soil, most likely with a pH between 5 and 6.

If your soil doesn’t react at all it is neutral with a pH of 7 and you are very lucky!

This test was fun to do. After I added the vinegar there was no reaction in my bowl and I thought my kitchen science experiment wouldn’t work. Then I added distilled water to another bowl of soil and poured on just a sprinkling of baking soda. Instant fizz! So much fizz that I could see it immediately and hear it working. There’s no doubt – I have acidic soil in my new garden.

#2 – You Can Do a Red Cabbage Water pH Test at Home

Measure 2 cups of distilled water into a saucepan. Cut up and add 4-6 red cabbage leaves. Simmer for 10 minutes. Remove from heat and allow it to sit for up to 30 minutes.

Strain off the liquid – which will be purple/blue. This will have a neutral pH of 7.

To test: Add 2 teaspoons of garden soil to a jar and a few inches of cabbage water. Stir and wait for 20-30 minutes. Check the color. If it turns reddish/pink, your soil is acidic. If it is seablue/ yellow-green, your soil is alkaline. Neutral soil is usually purplish/blue.

Don’t add too much soil to each jar as the cabbage juice may turn grayish-black and you’ll need to redo the test. Here’s a chart with what colors you should expect for each pH reading.

Red Cabbage Juice Indicator Colors (Photo courtesy of

Important Notes Before You Start Off

  • Why is it important to use red cabbage in this test? Unlike white cabbage, red cabbage contains a coloring compound, anthocyanin, which turns yellowish green when in a basic (alkaline) environment (pH > 7.0) and reddish pink when in an acidic environment (pH < 7).
  • You can use the red cabbage pH test to test your tap water hardness. Hard water is usually alkaline (pH 8 or more) due to the minerals in it. That’s why it is critical to perform the cabbage soil test with distilled water, which has a neutral pH.
  • Tap water or well water may be too alkaline while rain water may be too acidic (it usually stands at 5.6 pH) for this DIY soil pH test.
  • Before you start testing the soil, you can test the pH of various ingredients around the house and garden in small cups too see which color is associated with which pH number: Egg white has pH 8, baking soda (1 tsp) has pH 8.4, black tea – pH 4.9, cow’s milk 6.5 – 6.7 pH (depending on how it’s treated), potatoes – pH 6.1, vinegar pH 2.5, coffee grounds are very close to pH neutral (6.8) so they are often used as a natural buffer in the cabbage soil test (after 30 minutes they should turn cabbage juice clear).

Is Red Cabbage Better than Litmus Paper or a Digital Meter?

Surprisingly, the answer is yes. Litmus paper is paper treated with a mix of dyes derived from lichesn, which change colors, depending on the pH. While litmus paper has little color variety (red for acidic conditions, purple for neutral, and blue for alkaline conditions), red cabbage has a much wider range of colors, which can help better estimate the pH in soil.

Also, the red cabbage soil test is believed to be even more accurate than digital meters as it has some clear advantages:

  • Unlike a meter, the cabbage test allows the soil to soak in the juice and release elements that after interacting with anthocyanin in the cabbage juice will lead to a more accurate result;
  • Cabbage doesn’t require calibration after each soil sample; even some of the most expensive digital meters need to be calibrated before each test, as a result you can test as many soil samples as you wish at the same time;
  • It is cheaper (around $1 versus $15-$200).

Acidic Soil-Loving Plants

There are quite a few fruit and vegetable plants that thrive in acidic soil. These include:

  • Blueberries
  • Beans
  • Broccoli
  • Beets
  • Bok choy
  • Garlic
  • Kale
  • Lettuce and other leafy greens
  • Parsley
  • Peas
  • Potatoes
  • Onions
  • Spinach

However, you should do some research before adding these plants to your garden as some may love acidic conditions while others may only tolerate them. You could also consider crop rotation as acidic soils tend to become depleted of critical nutrients such as phosphorus and packed with elements that may prove poisonous to plants, such as aluminum.

You can read more on crop rotation and why it is a must for any organic vegetable garden in our “Vegetable Families and Crop Rotation” post.

Alkaline Friendly Plants

If your soil tests slightly alkaline (pH between 7 and 8) you’ll be able to easily grow these vegetables without making amendments:

  • Artichoke
  • Asparagus
  • Brussels sprouts
  • Cabbage and Chinese cabbage
  • Cantaloupe
  • Grape vines
  • Leeks
  • Lima beans
  • Mustard and other leafy greens
  • Orange
  • Peach tree
  • Spinach
  • Sugar beets
  • Swiss chard
  • Turnips

To Wrap It Up

Knowing the pH of your soil will help your plants grow by absorbing nutrients better from the soil. Their ability to do it depends on the nature of the soil and its combination of sand, silt, clay, and organic matter.

The makeup of soil (soil texture) and its acidity (pH) determine the extent to which nutrients are available to plants. Use these 2 ways to test soil pH and have a great garden this year.

Other soil building posts you might like: Mason Jar Soil Test – How to Improve your Soil Structure this Winter – SMART Composting – Turn Your Spoil into Soil – Improve Garden Soil – 10 Drought Buster Garden Strategies

Leave a Reply

Your email address will not be published. Required fields are marked *