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Soil pH and Vegetable Crop Nutrition

Soil pH test meter

Vegetable crops and other plants get most of the nutrients they need from the soil; the nutrients are dissolved in soil moisture and taken up by roots (other nutrients come from the air and are taken in by plant leaves).

A plant root’s ability to absorb mineral nutrients is affected by the chemical balance of what is called the soil solution; soil solution is a mix of mineral nutrients and soil moisture. If a soil mineral can’t dissolve in soil moisture it will not be available as a nutrient for uptake into the plant.

Soil acidity and alkalinity

A mineral nutrient’s ability to dissolve in soil water is chemically affected by the soil’s acidity or alkalinity, essentially the amount of calcium—chalk and lime—in the soil. If soil is too acidic or too alkaline many mineral nutrients will not dissolve in soil moisture.

pH scale

pH is a measure of the soil’s acidity or alkalinity. The pH scale or measuring stick numbers from 1 to 14:

  • 1 is the most acidic
  • 14 the most alkaline
  • 7 on the pH scale is neutral

(For reference lemon juice has a pH of 2; orange juice has a pH of 4; baking soda has a pH of 8.5 and ammonia has a pH of 11.5.)

Most nutrients needed by vegetables become chemically available when the soil pH falls between 6.0 and 7.5.

Plant nutrients in the soil

The most important mineral nutrients essential for plant growth are nitrogen, phosphorus, and potassium. Nitrogen promotes leafy growth; phosphorus is important for root growth and the production of flowers, fruits, and seeds; potassium is necessary for the development of leaves and roots and all-around plant health. Other nutrients taken up through the soil solution are calcium, sulfur, and magnesium in moderate quantities and trace quantities of iron, manganese, zinc, boron, copper, and molybdenum.

How plant nutrients get “locked”

When the soil pH falls below 5.0 and becomes moderately acid, nitrogen, phosphorus, and potassium cannot be dissolved in the soil solution and become chemically unavailable or “locked up.” Calcium and magnesium also become unavailable in moderately acid soil. When the soil pH rises above 7.5 and becomes increasingly alkaline, iron, manganese, and phosphorus become unavailable or “locked up.”

Microorganisms and soil acidity and alkalinity

Soil acidity and alkalinity also affect soil-dwelling microorganisms and earthworms which are essential to the decay cycle and soil health. Many microorganisms become less active as the soil becomes more acidic, and they stop activity altogether when the pH falls below 4.5.

A soil pH meter will have a dial like this.

Testing the soil

A soil sample from your garden can be tested by a soil lab. A lab test will make specific recommendations on how to correct soil that is too acid or too alkaline. You can also test soil pH yourself with a home soil test kit or a portable pH meter.

Helping the soil pH

The surest way to maintain a pH good for growing vegetables, herbs, and fruits—a pH between 5.5 and 7.5–is to regularly add aged compost and manure to your garden. Adding organic matter to the soil tends to make both acidic and alkaline soils more neutral. If your garden has healthy-looking plants and plenty of earthworms, you can be assured your soil pH is where it needs to be.

Crops listed by soil pH requirements

This list will allow you to group plants according to their soil pH tolerances. You will find that in the lists below, some plants may be repeated if they have a wide soil pH range tolerance; that is some plants will grow equally well in acid or alkaline soil.

Acid Soil Crops: The following crops prefer a pH of 4 to 5.5:

  • Blackberry (5.0-6.0)
  • Blueberry (4.5-5.0)
  • Cranberry (4.0-5.5)
  • Parsley (5.0-7.0)
  • Peanut (5.0-7.5)
  • Potato (4.5-6.0)
  • Raspberry (5.5-6.5)
  • Sweet potato (5.5-6.0)

Somewhat Acid Soil Crops: The following crops prefer require a somewhat acid soil; they can tolerate a pH of 5.5 to 6.5:

  • Apple (5.0-6.5)
  • Basil (5.5-6.5)
  • Carrot (5.5-7.0)
  • Cauliflower (5.5-7.5)
  • Chervil (6.0-6.7)
  • Corn (5.5-7.5.)
  • Cucumber (5.5-7.0)
  • Dill (5.5-6.5)
  • Eggplant (5.5-6.5)
  • Garlic (5.5-7.5)
  • Melon (5.5-6.5)
  • Parsley (5.0-7.0)
  • Pepper (5.5-7.0)
  • Pumpkin (6.0-6.5)
  • Radicchio (6.0-6.7)
  • Radish (6.0-7.0)
  • Rhubarb (5.5-7.0)
  • Sorrel (5.5-6.0)
  • Squash, winter (5.5-7.0)
  • Sweet potato (5.5-6.0)
  • Tomato (5.5-7.5)
  • Turnip (5.5-7.0)

Moderately Alkaline Soil Plants: The following crops will tolerate a pH of 6.0 to 7.0 or greater:

  • Artichoke (6.5-7.5)
  • Arugula (6.5-7.5)
  • Asparagus (6.0-8.0)
  • Bean, pole (6.0-7.5)
  • Bean, lima (6.0-7.0)
  • Beet (6.0-7.5)
  • Broccoli (6.0-7.0)
  • Broccoli rabe (6.5-7.5)
  • Brussels sprouts (6.0-7.5)
  • Cabbage (6.0-7.5)
  • Cantaloupe (6.0-7.5)
  • Cauliflower (6.0-7.5)
  • Celery (6.0-7.0)
  • Chinese cabbage (6.0-7.5)
  • Celeriac (6.0-7.0)
  • Celery (6.0-7.0)
  • Chinese cabbage (6.0-7.5)
  • Chive (6.0-7.0)
  • Cilantro (6.0-6.7)
  • Claytonia (6.5-7.0)
  • Collard (6.5-7.5)
  • Cress (6.0-7.0)
  • Endive/escarole (6.0-7.0)
  • Fennel (6.0-6.7)
  • Gourd (6.5-7.5)
  • Horseradish (6.0-7.0)
  • Jerusalem Artichoke/Sunchoke (6.7-7.0)
  • Kale (6.0-7.5)
  • Kohlrabi (6.0-7.5)
  • Leek (6.0-8.0)
  • Lettuce (6.0-7.0)
  • Marjoram (6.0-8.0)
  • Mizuna (6.5-7.0)
  • Mustard (6.0-7.5)
  • Okra (6.0-7.5)
  • Onion (6.0-7.0)
  • Oregano (6.0-7.0)
  • Pak choi (6.5-7.0)
  • Parsnip (5.5-7.5)
  • Pea (6.0-7.5)
  • Radicchio (6.0-6.7)
  • Radish (6.0-7.0)
  • Rhubarb (6.5-7.0)
  • Sage (6.0-6.7)
  • Salsify (6.0-7.5)
  • Spinach (6.0-7.5)
  • Squash, summer (6.0-7.0)
  • Sunflower (6.0-7.5)
  • Sunflower (6.0-7.5)
  • Swiss chard (6.0-7.5)
  • Tarragon (6.0-7.5)
  • Tomatillo (6.7-7.3)
  • Watermelon (6.0-7.0)

Very Acid to Alkaline Soil Tolerant Plants: The following crops have the greatest tolerance for a wide range of soil acidity or alkalinity, from about 5.0 to 7.0:

  • Alpine strawberry (5.0-7.5)
  • Carrot (5.5-7.0)
  • Cauliflower (5.5-7.5)
  • Corn (5.5-7.5)
  • Cucumber (5.5-7.0)
  • Dill (5.5-6.7)
  • Endive/Escarole (5.8-7.0)
  • Garlic (5.5-7.5)
  • Parsley (5.0-7.0)
  • Parsnip (5.5-7.5)
  • Peanut (5.0-6.5)
  • Pepper (5.5-7.0)
  • Rutabaga (5.5-7.0)
  • Squash, winter (5.5-7.0)
  • Tomato (5.5-7.5)
  • Turnip (5.5-7.0)

Click on These Related Articles on Soil pH:

Understanding Soil pH

How to Test Your Soil

Adjusting Soil pH

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.

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