How To Test Soil pH

Soil fertility and soil pH can be intimidating to both new and experienced gardeners. But your soil isn’t as mysterious as you think, as long as you start by having a soil test done. “Testing your soil allows you to make sure you have the optimal conditions for what you’re growing,” says Barbara Smith, consumer horticulture extension agent at the Home and Garden Information Center at Clemson University. “Without a soil test, you may add product that your garden doesn’t need, which can be detrimental to some plants, or you may spend money on soil amendments that aren’t necessary.”

One of the things you can learn from a soil test is your garden’s pH. Soil pH is a measure of how acidic or alkaline your soil is, ranging from 0 to 14, with 7 considered neutral. Less than 7 is acidic, while greater than 7 is considered alkaline soil. Knowing this is important because different types of plants like different soil pH ranges. For example, plants such as blueberries and azaleas prefer acidic soil and will not thrive if pH is too high, says Smith. Nitrogen testing usually is not included in a standard test because the levels of available nitrogen are variable due to its mobility in the soil. 

Standard soil tests also measure the levels of primary nutrients such as phosphorus (P) and potassium (K); secondary nutrients such as calcium, and magnesium; and micronutrients plants need in very small amounts, such as zinc and manganese. In addition, test results provide customized information about what amendments your lawn, perennials, and vegetables need to grow vigorously, says Smith.

How To Test Soil pH

Our expert recommends to go through your local university coop extension office. Every state has its own extension service (find yours here). “Your local agent is familiar with the soil regionally, and the equipment that’s used to evaluate soil samples is calibrated for the types of soil and growing conditions in your area,” says Smith. That means recommendations are based on local conditions and won’t be helpful to you if you don’t live in that area.

A home testing kit won’t give you the full picture. You can buy a soil test kit at big box retailers, but it’s not going to give you all the information you need. “It may give you an accurate soil pH, but it won’t break down the other specific elements or tell you what you need to do to adjust them,” says Smith.

How To Collect A Soil Sample

1. Use a clean garden trowel to collect scoopfuls, about ¼-cup each, from different parts of your yard. Collect six to eight samples from different spots.
2. Make sure to dig deep enough. Lawn samples should be taken three to four inches deep. Samples for perennial beds or vegetable gardens should be collected at a depth of six to eight inches.
3. Combine the samples in plastic zipper-top bag. Remove any plant debris.
4. Make sure soil is dry, because it can’t go through the testing equipment when wet. If it’s damp, spread it out on something like a cookie sheet and let it air-dry in the shade or in the garage before shipping. Keep it out of direct sunlight.
5. Ship the sample to your lab. Soil labs usually have a form you fill in to indicate what kind of crop you’re growing. This will guide the lab’s recommendations for what amendments you should add and at what rates.
6. Do separate tests for each type of planting area. Don’t mix samples from your lawn, shrub and perennial beds, and vegetable garden. These areas may have been fertilized differently, which can skew results.

Your soil tests results should arrive within a few weeks. If you need help interpreting them, contact your county extension agent.

The Best Time of Year To Test Soil pH

You can test soil any time of year, but the best time to test your soil is a few months before you want to plant, in case you need to make adjustments to pH. That’s because it takes time for any soil amendments you might need to have an effect on the pH level, says Smith.

 How Often To Test Soil pH

There’s no one-size-fits-all recommendation, but generally, most experts recommend every one to two years. But if you had to add amendments to adjust soil pH, for example, repeat the test in a few months, says Smith. Anytime you change anything, you’ll need to check levels again.