Understanding Soil pH
To achieve a thriving garden worthy of a humble-brag, healthy soil is number one. However, even great soil can cause problems if the pH is off. Soil pH affects how well plants take in nutrients. If your plants look droopy or their leaves turn yellow, the issue might be a pH imbalance, not a nutrient deficiency.
And even the greenest of thumbs can be confused by soil pH (especially those kits) if biology and chemistry weren’t their forte in grade school—and even if they were. Hopefully, the following breaks it down in a digestible, easy-to-understand way.
What Is Soil pH?
Soil pH indicates whether your soil is acidic or alkaline, measured on a scale from 0 to 14.
pH below 7 means acidic soil
pH above 7 means alkaline soil
pH of 7 is neutral
(One easy way to remember this is: below seven = acid heaven. You’re welcome.)
Most vegetables grow best in slightly acidic soil, usually between 6.0 and 7.0. In North Carolina, soils are often more acidic because of heavy rain and old clay soils.
If the pH is too acidic or too alkaline, plants have trouble absorbing essential nutrients such as calcium, magnesium, phosphorus, and nitrogen, even when they are present in the soil.
Signs pH is Off
Testing soil is obviously the most accurate, scientific way to know pH, but there are also some visible conditions that can show something is off, too:
Leaves turning yellow
Stunted growth
Fruit production slows down or stops
Blossom-end rot in plants like tomatoes and peppers
Weak roots
Unwanted moss growth in compacted areas/lawns
Plants that were doing fine but have become dull or lackluster
Many gardeners add more fertilizer with hopes it’ll fix the problem, but sometimes the real issue is a pH imbalance that prevents plants from absorbing key nutrients.
Soil Tests
Getting your soil tested is a smart step. Rather than guessing, a test can measure pH and nutrient levels.
For those living in North Carolina, the Cooperative Extension offers affordable soil testing, which is a great way to get expert advice. And not to worry for anyone living elsewhere, because every state has an Extension office, which can be found on Extension.org. Home pH meters and kits can give a rough idea, but lab tests are more accurate and often include advice for your specific plants.
Understanding At-Home Soil pH Tests
For gardeners using at-home soil tests like Rapitest or other DIY kits, the results might seem confusing at first. As mentioned, these tests are not as accurate as lab tests, but they can still give a good idea of the soil’s condition and help spot major pH problems.
Most at-home tests work by mixing soil with water and a testing solution or capsule. The solution changes color depending on the soil’s acidity or alkalinity, and the color is then compared to a chart to estimate the pH.
How to Get Accurate Results with Soil Tests
At-home tests are only as good as the soil sample(s) being used. There are a number of things that will help get better results from these kits:
Collect soil from multiple spots throughout the garden rather than a singular location.
Remove “junk” such as mulch, roots, or large debris before testing.
Test soil that is slightly moist but not soaking wet.
Carefully follow the kit instructions, especially regarding water and timing.
Avoid testing immediately after fertilizing or liming, since this can give false readings.
What the pH Numbers Mean
Most Rapitest-style kits measure pH on a scale from 4 to 8:
4–5 = strongly acidic
5.5–6.5 = moderately acidic
6.0–7.0 = ideal range for many vegetables
7 or more = alkaline
Here are some examples of these numbers in reality:
Blueberries prefer acidic soil with a pH ranging from 4.5 to 5.5.
Most garden vegetables grow best between 6.0 and 7.0.
Lavender, rosemary, and some other herbs tolerate slightly more alkaline soils.
Why pH Matters
A soil test may reveal that nutrients are present, but if the pH is too high or too low, plants will have a hard time absorbing them. This often leads people to continue fertilizing—without any noticeable improvement.
For instance, low pH can reduce calcium availability, contributing to blossom-end rot; high pH can hinder iron availability to plants, causing yellowing leaves.
How to Raise Soil pH
If a soil test reveals that the soil is too acidic, there are plenty of methods to raise the pH. Lime is a popular amendment that can gradually improve soil. A couple of common options include types of lime:
Agricultural lime (calcitic lime) is a standard option for improving soil pH.
Dolomitic lime raises pH and adds magnesium, which is another essential nutrient for plants.
If using lime, timing needs to be factored in because it works slowly, so it’s best to add it a few months before planting. Using too much lime can also cause problems, so always follow the recommendations from your soil test. It’s a delicate dance!
How to Lower Soil pH
Lowering the soil’s pH is a bit harder and takes more time, but there are also many ways to do it.
Elemental sulfur is a common choice for acidifying soil.
Pine needles or pine bark mulch can not only help with pH, but also add organic matter.
Compost and organic matter are great as regular additions to help improve overall soil health.
Cottonseed meal can also help make the soil more acidic.
Building Better Soil Over Time
Learning about soil pH is a powerful tool for “reading” a garden and identifying problems that rear their ugly heads, in turn helping gardeners grow their plants bigger and better. With some practice (and a lot of patience), anyone can grow a bountiful garden with fewer headaches.
It’s also worth reiterating that perfect soil pH isn’t necessary for growing healthy plants. Many gardeners worry about hitting an exact number, but most crops can handle a range of pH levels.
Soil health is about more than just pH. Things like soil structure, organic matter, drainage, microbes, and how well the soil holds water all help plants grow their best.
A long-term approach is important on all fronts. Usually, making small changes over time works better than trying to fix everything at once. And one way to do that (it can’t be said enough) is by adding compost regularly, which can help more than anything. It improves all of the aforementioned factors: soil structure, beneficial microbes, and consistent moisture levels. Adding that, along with mulching, will also gradually and naturally balance pH extremes. Compost really is the magic elixir.
If native soils aren’t cooperating, or there’s the issue of heavy clay and/or poor drainage, raised beds can also be a solution. With a little work up front, they can save a lot of time, money, effort, and heartache in the end—they’re a workaround that’s nothing to scoff at.
So remember, soil improvement is much like the tortoise in the proverbial race. Many gardening issues develop slowly, and creating healthy soil typically takes multiple seasons. Take time to observe plants and make thoughtful amendments, and over time, they’ll build up soil that supports vibrant, healthy growth.
Happy growing!
