How to Test Soil pH (And How to Make Soil More Acidic For Healthy Crops)

Remember your high school chemistry class? The chapter about pH and litmus testing? Bet you didn’t think you’d ever have to dig that knowledge up again, but pH actually plays a really big role in soil and plant health.

What exactly does pH have to do with gardening? The pH levels in the soil affect plants in two distinct ways: nutrient availability and the presence of soil microorganisms. If soil pH is off, plants will struggle to absorb nutrients (no matter how much fertilizer you add) and the soil itself won’t be able to support a healthy ecosystem of microorganisms and beneficial bacteria.

Soil pH isn’t something that should be overlooked, and should be checked each year when you send a soil sample off to a lab for testing. Fortunately, testing soil pH is even easier than testing soil composition and is just as simple to adjust once you have your results.

Understanding soil pH

What is soil pH?

You learned it in school—the pH scale measures the acidity of any substance. (In case you need a refresher: the scale ranges from 0 to 14, with 7 signifying a neutral pH, greater than 7 is alkaline, and less than 7 is acidic.)

How does soil pH affect plant growth?

Soil pH directly correlates with which nutrients are water-soluble and available for plant absorption.

Nutrient availability

In an article titled Acidifying Soil published by Oregon State Extension, author Kerry Locke writes that “Nutrients such as zinc, manganese, phosphorus, and iron are less soluble in water when soil pH is above 7.5. Thus, they are less available to plants in higher pH soil even if they are plentiful in the soil.”

Some nutrients are only water-soluble in acidic conditions, and other nutrients absorb better in alkaline conditions. Which nutrients are needed by certain plants determines which soil pH those plants need to thrive.

Presence of microorganisms

Not only does soil pH affect nutrient absorption levels, but it affects which microorganisms can live in the soil. The more microorganisms and beneficial bacteria inhabit the soil, the more nutritious the soil and the healthier plants growing in it will be.

What’s an ideal soil pH?

Soil pH is important because acidity impacts how plants grow. Most flowers, vegetables, and herbs prefer a slightly acidic to neutral soil between 6.0 and 7.0, although some perennial plants thrive in alkaline soils (geranium, lavender, and asparagus, to name a few).

A quick Google search will reveal what soil pH specific plants prefer—and our Soil Tester will also tell you!

How to use a Soil Tester

Analyzing soil pH at home has never been easier than with our Soil Tester. Here’s how to use the Soil Tester in three simple steps.

1. Simply pop an AA battery in the Soil Tester and set the switch to the “pH Analysis” position.
2. Next, stick the prongs down into the soil to be tested.
3. Wait one minute and the Soil Tester will reveal your results.

Once you have the results, reference the included pamphlet with 350 plants and their ideal pH requirements to determine which way you need to adjust the soil.

It’s good practice to test multiple locations in the same garden bed and take the average before adjusting the soil. If you have raised beds, test the soil pH in each bed, as it could vary from bed to bed.

Analyzing soil composition

Once you’ve tested your soil pH, you can also analyze soil composition. To test soil fertilizer levels, simply clean the prongs and reset the tester by moving the switch to the “Fertilizer Analysis” setting. Insert the prongs into the soil and wait one minute before reading the results.

Although the Soil Tester is the only tool you need to analyze and adjust soil pH, you can get a detailed assessment of your garden soil from a university research lab if you prefer.

Sending off a soil sample

Call or visit your local Agricultural Extension office to pick up a box and a mailing address of where to send your soil sample. To take a soil sample, locate a few different areas in your garden that you want to test.

At each location, dig into the soil at least six inches and transfer the dirt into a plastic bag (don’t let any grass fall into the bag if you can help it) ensuring no grass or topsoil is included. Repeat the process at the next location, labeling each bag to correspond with the correct area. Finally, package the samples and send them off to the appropriate address.

Testing soil pH at the right time

While you can technically test your soil at any time, fall is the best time of year to analyze soil pH since you’ll have plenty of time to adjust soil pH and composition for the next growing season. Some soil amendments (including lime) take between three and six months to go into effect, so a spring test may not actually bring the results in time for the growing summer season.

However, consistency is arguably more important than perfect timing. Whatever time of year you test your soil pH, test it again around the same time the following year. If you miss the date by a few weeks or months, don’t fret—it’s still worth testing your soil whenever you can get to it.

Soil testing and adjusting don’t bring immediate results—but the results of keeping an eye on your soil and giving it what it needs definitely pay off over time. Soil that has been monitored and amended with nutritive additives will be able to grow far more plants over time than soil that isn’t regularly tested and maintained.

Adjusting soil pH with amendments

The best way to adjust soil pH (in either direction) is by adding acidic or alkaline soil amendments.

It’s as simple as this: if your soil is too acidic, add something more alkaline to raise the pH. If your soil is too alkaline, add something acidic to lower soil pH.

Acidic soil amendments

Add acidic substances to the soil to lower pH (and increase organic matter in the soil).

• Compost

The exact pH level of compost varies depending on the contents of the compost and how it was made, but most compost is only slightly acidic. Even though compost won’t move the pH needle drastically, it’s still worth applying to your garden, since compost adds organic matter and improves soil drainage and composition.

If you can find a good source of organic compost, pile it on in a layer about an inch thick. use a broadfork or tiller to turn the compost back into the soil, and watch the soil come back to life.

• Peat moss

One of the more acidic soil amendments, Sphagnum peat moss has a pH between 3.0 to 4.5, so a little goes a long way when lowering soil pH. Peat moss adds aeration to compacted soils and its fine texture makes it an excellent seed-starting medium. 

Unfortunately, the mining rate at which peat moss is mined from Canadian bogs raises some environmental concerns, and coco coir might be a more sustainable alternative.

• Sulfur

It’s recommended to add no more than three ounces of sulfur for each square foot of garden. Of the two different types of sulfur, ferrous sulfate is rich in iron, while aluminum sulfate is a faster-acting soil acidifier. To avoid damaging the soil, always mix sulfur with compost to dilute the presence of heavy metals.

Alkaline soil amendments

These alkaline soil amendments help raise pH levels, making the soil less acidic.

• Lime

Limestone is the most common alkalizing soil amendment since it’s easy to find and apply over large fields. Limestone amendments to soil come in two forms—calcitic or dolomitic. Dolomitic lime has higher magnesium content, but both types provide calcium and raise soil pH.

Soil experts recommend adding about 40 pounds of lime per 1000 square feet to raise soil pH by one numeral. The only downside of using lime is that it can take a year or more to see results.

• Wood ash

Another great option for raising soil pH, wood ash works much faster than lime and is just as easy to find. In addition to alkalizing soil, wood ash contains many other micronutrients: calcium, magnesium, potassium, phosphorus, zinc, and copper.

• Baking soda

This common kitchen cabinet staple has a pH of 8.0, so you can use baking soda to make your garden soil more alkaline. Mix one tablespoon of baking soda per one gallon of water and pour the solution into a garden sprayer. Spray the mixture over your garden bed, soaking the soil thoroughly. 

Baking soda isn’t an ideal soil amendment for a large garden but can be used in a pinch to raise soil pH levels over small areas.

The common saying, “too much of a good thing is bad,” is true with soil pH, too. Even though plants prefer slightly acidic soil, soil that is overly acidic may actually stunt plant growth by limiting nutrient availability and decreasing the presence of beneficial microbes.

Soil that is too alkaline has a similar effect, so err on the side of caution when amending soil. And always, always wear gloves, safety glasses, and a facemask when handling chemicals!

Soil pH plays a critical role in soil and plant health—fortunately, monitoring it is an easy process.