How to Measure and Adjust pH in Garden Soil

Soil pH is defined as the soil’s overall acidity. More specifically, it refers to the potential hydrogen ions present, which itself is partly determined by soil type and the containment of any lime (calcium).

When soil is too acidic (low pH) or alkaline (high pH), any present nutrients become locked up or unavailable. Correcting your garden’s acidity level has the same effect as adding fertilizer, as it unlocks plant nutrients already present (plus, it is more cost effective!).

A pair of man's hand inspects black soil.

In this article, we discuss the optimal pH levels for various vegetables, fruits, flowers, and ornamentals, plus walk through measuring and adjusting your soil as needed.

How to Measure Soil pH

Farmers used to taste their dirt to determine its acidity. A sweet taste or smell, and it was alkaline. A sour taste meant it was acidic. Fortunately, these days we have more sanitary ways of testing our garden’s levels!

The pH scale ranges 0 to 14. A pH lower than 7.0 signals an acidic soil, while one higher than 7.0 is alkaline. A score of 7 is neutral. While some plants thrive in an acidic environment, others do better when planted in a more alkaline space.

It is recommended that you test your soil’s pH levels once per year, before the fall planting season. You can accomplish this any number of ways, including with common household items and an inexpensive pH testing kit purchased from your favorite gardening store.

Using your testing kit, follow the simple steps below:

  1. Dig a small hole about four inches deep, and take approximately one tablespoon of soil
  2. Place the soil in a small bowl, and mix it thoroughly along with some distilled water
  3. Dip the test strip from the testing kit into your combined mixture, allowing it to soak for 20-30 seconds
  4. Compare the resulting color on the test strip to the key provided with your kit

The color that appears on your test strip will tell you how acidic or alkaline your soil currently is. Depending on the results, and depending on what you would like to grow, you may need to adjust your soil.

See: Test Garden Soil Yourself

How to Adjust Soil pH

To raise or lower soil’s acidity, you can use either limestone (calcium) or elemental sulfur. There are other materials that will do the job also, but the aforementioned are the most widely used. Both can be purchased online, at your favorite nursery, or in big box home improvement stores.

Limestone is added to raise acidity because limestone is essentially calcium and calcium reacts with water to yield hydroxyl ions. This is a process known as hydrolysis.

Meanwhile, sulfur reacts with bacteria in the ground to produce sulfuric acid, which releases hydrogen ions. This lowers the pH level, thus causing the soil to become more acidic.

How to Use Lime to Increase pH in Soil

To increase your pH by 1.0 point and make your garden more alkaline:

  • Add 4 ounces of hydrated lime per square yard in sandy soils
  • Add 8 ounces of hydrated lime per square yard in loamy soils
  • Add 12 ounces of hydrated lime per square yard in clay soils
  • Add 25 ounces of hydrated lime per square yard in peaty soils

Ash, bone meal, or crushed oyster shells will also help to raise soil pH levels.

Using Sulfur to Lower pH in Soil

If your soil needs to be more acidic, elemental sulfur may be used if it is available.

To reduce by 1.0 point:

  • For sandy soil, mix in 1.2 oz of garden sulfur per square yard
  • For all other soils, mix in 3.6 oz per square yard

Composted leaves, wood chips, sawdust, leaf mold, and peat moss can also be used.

Optimal Soil Ph for Fruits and Vegetables

Almost all vegetables prefer soil that is well-drained, rich in organic matter, and slightly on the acidic side. A safe pH range for almost all vegetables is 6.0 to 6.5.

However, there are exceptions to all rules, and optimal results require more precise tracking and maintenance. Use the chart below to find the minimum and maximum levels for various fruits and vegetables.

pH for Vegetables and Fruit

Common Vegetable & Fruits
Artichoke6.5 -7.5
Asparagus6.0 -8.0
Bush Bean6.0 -7.5
Beets6.0- 7.0
Blueberries4.5 – 5.5
Broccoli6.0 – 7.5
Brussels Sprouts6.0 – 7.5
Cabbage5.8 -6.2
Cantaloupe5.5 -7.0
Carrots5.5 – 7.5
Cauliflower6.0 – 7.0
Celeriac5.5 – 6.5
Celery5.5 -5.5
Chicory5.0- 7.5
Corn5.5 -7.0
Cranberry3.5 – 5.0
Cucumber5.5 – 7.5
Eggplant5.5 – 6.0
Endive5.5 – 6.0
Garlic5.5 – 7.5
Horse Radish6.0 -7.0
Kale6.0 – 7.5
Kohlrabi6.0 – 7.5
Leek6.0- 8.0
Lentil5.5 – 7.0
Lettuce6.0- 7.0
Mushroom6.5- 7.5
Muskmelon5.8 -6.2
Mustard6.5 – 7.5
Onion6.0 -7.0
Parsnip5.5 -7.0
Peas6.0- 7.5
Peanuts5.0 -6.5
Peppers5.5 -7.0
Potato4.5 – 6.0
Raspberries5.6 – 6.2
Rhubarb6.0 – 6.8
Shallot5.5 -7.0
Soy Bean5.5 -6.5
Spinach6.0- 7.5
Tomato6.0 -6.8
Watercress5.0 -8.0
Watermelon6.0 – 6.8
PH for fruits and vegetables

pH for Flowers and Ornamentals

Flowers & Ornamentals
Amaryllis5.5 – 6.5
Azalea6.0 -7.5
Baby’s Breath6.0- 7.0
Balsam4.5 – 5.5
Begonia6.0 – 7.5
Caladium6.0 – 7.5
Candytuft5.8 -6.2
Canna5.5 -7.0
Carnation5.5 – 7.5
Chrysanthemum6.0 – 7.0
Cockscomb 5.5 – 6.5
Coleus5.5 -5.5
Cornflower5.0- 7.5
CornCosmos5.5 -7.0
Daffodil3.5 – 5.0
Dahlia5.5 – 7.5
Day Lily5.5 – 6.0
Easter Lily5.5 – 6.0
Four-O-Clock5.5 – 7.5
Foxglove6.0 -7.0
Geranium6.0 – 7.5
Gladiolus6.0 – 7.5
Hollyhock6.0- 8.0
PH for flowers
Iris6.5 – 7.0
Larkspur6.5 – 7.0
Lupine6.5 – 7.0
Marigold6.0 – 7.5
Nasturtium6.5 – 7.0
Narcissus6.0 – 7.5
Pansy6.5 – 7.0
Perwinkle6.5 – 7.0
Petunia6.5 – 7.0
Phlox5.0 – 6.0
Poppy6.5 – 7.0
Salvia6.0 – 7.0
Shasta Daisy6.0 – 8.0
Snapdragon6.0 – 7.5
Sweet Alyssum6.5 – 7.0
Sweetpea6.5 – 7.0
Sweet William6.5 – 7.0
Tuberose6.0 – 7.0
Tulip6.0 – 7.0
Verbena6.0 – 8.0
Zinnia5.5 – 7.5

A Simple Test for Thriving Plants

If your fruits, vegetables, flowers, or ornamentals aren’t growing quite as well as they should be, your soil’s pH levels may be to blame. Testing your garden’s soil is easy with inexpensive testing kits, while widely available ingredients like limestone and elemental sulfur can work wonders to adjust acidity as needed. Be sure to bookmark the above charts and refer back to them as you test your soil or expand your garden.