How to Test Soil pH Before Planting — and Why You Should
Just like water and sunlight, soil plays a crucial role in the success of garden plants and crops, containing all the essential minerals that encourage growth. However, this also means that the opposite is true — if your soil isn't suited to the plants you're trying to grow, you're in for a difficult time. Testing soil pH is a simple and effective way to get a read on soil quality and make necessary changes before you sow your seeds. The best part? Anyone with a basic understanding of the pH scale and a few simple tools can perform these tests.
What is Soil pH? Why Does it Matter?
Soil pH refers to how acidic or alkaline (basic) your soil is. Acidic and basic refer to the two ends of the pH spectrum, a scale that ranges from 0-14, with 0-7 being acidic and 8-14 being basic. Anything between 6 and 8 is neutral. The number of positively charged hydrogen atoms in a substance determines its pH — the more hydrogen atoms there are, the more basic the substance is. An example of an acid would be orange juice, while a common base is baking soda.
Several different factors can affect pH, including climate, the type of rocks the soil formed from (like granite or limestone) and even the kinds of plants that were previously grown in an area (or the ones currently living there). For example, soil is likely to be more acidic if an area receives a lot of precipitation, has soil derived from shale or has a lot of trees growing in it. On the other hand, if your area is more arid, has soil derived from limestone and is lacking in trees, the soil will most likely be alkaline.
So why does all that matter? Because pH level determines how well plants can absorb the soil's nutrients. All plants are different, with some thriving in more alkaline soils and others preferring something more acidic. If you don't cater to those needs and correct the soil, your plants won't be able to absorb the nutrients they need, or they will absorb them to the point of toxicity. Either way, without testing soil pH, you could wind up with sickly, stunted plants.
How to Test Soil pH
Testing soil pH can help you easily get a read on your soil's pH level so you can correct it and foster a successful environment for your plants or crops. There are two main methods used to test soil acidity and several different tools for doing so effectively.
Methods
The first soil pH test method is direct testing, in which you test soil acidity right there in the field. To perform this test, you need to dig or drill a small hole in the ground about 6-8 inches deep, or 12 inches deep if you will be planting trees or shrubs. Then, add a small amount of distilled or deionized water to the hole until the soil becomes damp but not completely saturated. After the water has been absorbed, insert your chosen soil pH meter until a reading develops or the digital readout stabilizes. For small areas, take 5-10 samples; for larger areas, take 10-15. When finished, average out all your readings to determine the overall pH level or your soil.
Determine the soil pH by performing a slurry test. This soil pH test method requires fewer samples (only 1 or 2) and a few more steps to get a reading. Like direct testing, you will need to take soil from a few inches into the ground. Next, place the sample and an equal amount of distilled or deionized water into a container and stir for five seconds. After letting the sample rest for 15 minutes, stir the sample for another five seconds, and use your chosen soil pH meter to take your measurements.
Tools
There are a variety of tools designed to test soil acidity, some of which are more complicated than others but still fairly easy to use. The simplest soil pH tester is litmus paper, or pH test strips, which use pH-sensitive dyes to indicate a soil sample's pH level. These can be tricky to read when stained by muddy water or damp soil, and they can usually only measure pH in 0.5 units, so you won't get the highest level of accuracy. However, they're great for quick estimations.
A digital soil pH tester is the best way to test soil pH for high-accuracy results. Digital meters use a pH electrode to test soil acidity between 0.1 and 0.01 pH units and can be used in the field for direct testing or slurry testing. Just be sure to clean the meter before and after each use and to calibrate it periodically to ensure it maintains accuracy.
How to Alter Soil pH
If you've found that your soil is too acidic or basic for the kinds of crops you want to plant, fear not! There are many different ways to get your soil to the pH level you want. Sometimes all it takes is more frequent irrigation if you want to make the soil more acidic. But, if you want to make your soil more basic, you can try treating it with everything from calcium carbonate to eggshells (although eggshells may not be feasible if you're working with a large area).
Use these soil treatments to make your soil less acidic:
- Calcium carbonate
- Eggshells
- Lime
- Wood ash
Use these treatments to make your soil less alkaline:
- Calcium chloride
- Gypsum
- Iron sulfate
- Sulfuric acid
Plants & pH
Even if you'll be growing in a high tunnel greenhouse or using propagation pots, it's still advisable to test pH before sowing your seeds. Check out the optimal pH levels for some of the most common high tunnel crops.
| Crop | pH |
|---|---|
| Beets | 6.0-7.5 |
| Blueberries | 4.5-5.5 |
| Carrots | 5.5-7.0 |
| Cucumbers | 5.5-7.0 |
| Lettuce | 6.0-7.0 |
| Peppers | 5.5-7.0 |
| Radishes | 6.0-7.0 |
| Raspberries | 5.5-7.0 |
| Spinach | 6.0-7.5 |
| Tomatoes | 5.5-7.5 |