How to Test Your Garden’s Soil pH

Know your soil's pH in order to plant the right plant in the right place.

Woman planting.
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Overview
  • Total Time: 30 minutes
  • Skill Level: Beginner
  • Estimated Cost: $3.00 - $20.00

If you want healthy blueberries or asparagus, you'll need to know something about testing your soil pH, which stands for “potential hydrogen,” since the amount of hydrogen in the soil determines its acidity or alkalinity (or “sweetness”). A pH scale runs from 0 to 14, with 7.0 being considered “neutral.” Any number below that is considered acidic. Anything above is alkaline. The pH level of the soil determines how well plants can absorb nutrients, especially the key nutrients of nitrogen, phosphorus, and potassium, which are water-soluble only in relatively neutral soil.

pH scale

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Most plants can grow in soils with a pH between 5.5 and 6.5, but different plants do better in different soils. Blue hydrangeas thrive in soil with a pH range of 4.0-5.0, while artichokes prefer a pH range of 6.5-7.5. If your soil is too alkaline, you can add organic material such as a compost enriched with coffee grounds. The most common ways to “sweeten” your soil are to add wood ash or lime, the latter of which is made from calcium—the same element in stomach “antacid” products.

You can forgo almost all expense with either of the two DIY methods described below, but your results will not be as exact as using a pH test available from a garden center. pH test kits cost between $5 and $20. Kits costing less than $10 contain paper strips that turn different colors depending on the pH balance of your soil, and a color chart which corresponding pH levels. The more expensive tests are re-usable meters that probe the soil and give you an analog or digital readout.

When to Test Your Soil

Test your soil in the fall so that you have time for the soil to absorb any amendments you make to it before you begin planting in the spring. It can take 6 to 12 months for lime to dissolve completely in soil, and roughly the same amount of time for the nutrients in a compost to make their way to the root line. Test your soil again in the spring before you begin planting as well as during the growing season if your plants aren't doing well—their leaves are yellow or they are not producing fruit or flowers. Testing your soil every few years is also helpful, especially if you regularly add compost or mulch, which can change the soil's pH.

What You'll Need

Tools

  • 1 trowel or small shovel
  • 1 glassware (clean and rinsed)

Materials

  • 2 cups soil
  • 8 ounces distilled water
  • 4 ounces vinegar
  • 4 ounces baking soda
  • 1 red cabbage (for alternative method)

Instructions

  1. Dig Into Soil

    Dig 4-8 inches into your soil, which is the average depth of roots. Annual plants like vegetables will generally grow shallower roots than perennials, so dig according to what you're growing.

  2. Gather Soil for Testing

    Remove roughly one cup of soil and place it in a clean, glass container.

  3. Smooth Out Clumps and Remove Debris

    Remove any stones or debris and break up any large clumps of soil.

  4. Add Distilled Water

    Add 4 ounces of distilled water (which has a neutral pH), enough to moisten the soil completely.

  5. Add Vinegar and Observe

    Add 4 ounces of vinegar and stir. If the mixture foams or bubbles, you have alkaline soil.

Repeat steps 1 through 4, then add ½ cup of baking soda instead of vinegar. If the mixture foams or bubbles, you have acidic soil. If your soil bubbles in neither of the two tests, you have neutral soil, and most plants will do fine.

Alternative Method

  1. Chop Cabbage

    Chop red cabbage into roughly 1-inch strips, enough to make 1/4 cup.

  2. Boil Cabbage in Distilled Water

    Boil the cabbage in one cup of distilled water for 10 minutes, until the water turns purple.

  3. Remove Cabbage From Water

    Strain out the cabbage, keeping the water in the pot.

  4. Pour Water Into Glassware

    Pour the water into a clear glassware.

  5. Add Soil

    Add 2 tablespoons of soil to the water. If the water fails to change color, you have neutral pH. If it turns pink, your soil is acidic. If it turns blue, it's alkaline. The stronger the color, the more acidic or alkaline it is.

Soil pH Testing Tips

  • Especially if you are going to eat anything from your garden, a more comprehensive test than a pH test is recommended. Contact your state Cooperative Extension service or garden center about a test that can determine the nutrient levels and potential presence of contaminants in your soil.
  • Avoid amending your soil by adding peat moss, since peat bogs are essential to absorbing carbon dioxide from the atmosphere.
  • Grow the right plant in the right place. It's easier to grow acid-loving plants in acidic soil than it is to make acidic soil alkaline.
  • Test your soil in a number of places. If you have a variety of readings, you may want to do some of the tests over. If the variety of readings are correct a second time, then group your plants according to the different soil readings.