You are here

Test Soil to Find Its pH Value

The soil reaction, or measure of acidity or alkalinity, is based on a scale of 1 to 14 and is referred to as pH. A pH of 7.0 is neutral. Any values below 7.0 are acid, and any values above 7.0 are alkaline.

The ideal pH values for vegetable garden soils are 6.0 to 6.5. Vegetable plants do not grow well in acid soils with a pH of 4.5 to 5.5 or in alkaline soils with a pH above 7.5. Soil testing is the only way to know the pH of your garden soil. Contact your county Extension office for a container and instructions for taking a soil sample. There is a $8 fee for a complete analysis (pH plus nutrient analysis with lime and fertilizer recommendations) on each sample. The lime recommendation is the single most important piece of information on a soil test report.

In areas with high rainfall like Mississippi, soils are generally acid. However, there are exceptions (particularly in the Delta and Blackland Prairie) that prove the need for soil testing. Of the garden soils analyzed at Mississippi State University’s Soil Testing Laboratory from 1999 to 2004, 49 percent had a pH of 5.9 or below and needed lime. Twenty-six percent were in the range of 6.0 to 7.0.

The pH of the soil tells you if the soil needs lime. Where it is needed, limestone is the most effective and inexpensive aid available for soil improvement. The soil’s calcium and magnesium levels tell you what form of limestone—dolomitic (magnesium and calcium) or calcitic (calcium)—to apply. An acid soil that tested medium low to very low in magnesium should be limed with dolomitic (high magnesium) lime. An acid soil high in magnesium can be limed with either calcitic limestone or dolomitic limestone.

Acid soil results in poor plant growth, partly because of poor root growth. This means greater susceptibility to drought stress and less efficient use of soil nutrients. Plants growing in acid soil may show deficiency symptoms of several plant nutrients.

Apply lime well ahead of planting (2 to 3 months) to provide time for it to dissolve and change the soil pH. However, limestone begins to react as soon as it is incorporated and can be applied at any time to increase soil pH levels. Apply lime evenly over the entire area and work it into the top 4 or 5 inches of soil. Incomplete mixing may make future tests show a need for more lime, which can result in overliming and poor plant growth. Limestone not only raises the soil pH but improves fertility. Lime also improves the structure of clay soils and makes them easier to work.

Liming is not a once-in-a-lifetime event. Since soils limed to the proper pH return to their acid state with time, soil test every three years to determine if additional lime is needed. Sandy soils become acid again faster than clay soils.

Factors causing the soil pH to drop are listed below:

  • Using acid-forming fertilizers.
  • Leaching of lime from the soil by rain and irrigation water.
  • Decomposing of organic matter and release of organic acids.
A diagram showing the 6 steps to getting a good soil sample.
To get a soil sample for testing: (1) Use a spade or trowel to remove a slice of soil 6 inches deep; (2) Get similar
sections from other random places in your garden; (3) Put these samples in a pail; (4) Mix soil thoroughly in the
pail; (5) Remove about 1 pint of the well-mixed soil and dry it at room temperature; (6) Place dried soil in container.
Do not take samples where fertilizer has been spilled or manure has been piled. Do not include debris such as
leaves, sticks, or large stones in your sample. Deliver the soil sample to your county Extension office.

 

 

 

Print Friendly, PDF & Email

News

A man in a hat stands next to a bush covered in tomatoes growing inside a wire frame.
Filed Under: Coronavirus, Lawn and Garden, Insects-Vegetable Gardens, Vegetable Gardens May 1, 2020

More would-be gardeners than ever before are planting with hopes of a summer crop of vegetables, but getting to that harvest means handling the inevitable insect pests, weeds, disease and fertilizer needs.

A group of purple, yellow, and red petunias.
Filed Under: Lawn and Garden, Flower Gardens, Landscape Architecture, Vegetable Gardens April 27, 2020

With so many Mississippians staying at home more than usual, it’s the perfect time to start planning your summer landscape. 

A small branch with green leaves has several small, green avacados growing from it.
Filed Under: Flower Gardens, Vegetable Gardens April 13, 2020

Did you know that April is National Gardening Month? In my landscape, every month is gardening month, but it’s fitting to be officially celebrating as many people are gardening for the first time while they shelter in place.

A woman uses a hoe to tend a flower bed.
Filed Under: Fruit, Coronavirus, Lawn and Garden, Flower Gardens, Vegetable Gardens April 3, 2020

Interest in gardening has nearly kept pace with social distancing and self-isolation rates across the country as the COVID-19 pandemic has circled the globe.

A person spreading mulch in a flower bed.
Filed Under: Lawn and Garden, Flower Gardens, Landscape Architecture, Vegetable Gardens March 26, 2020

Everyone’s normal routine is being flipped upside down. Employees are working from home, kids are out of school, and social gatherings are postponed. Boredom and stress are setting in. Gardening to the rescue! 

Watch

Bachman's Heritage Cottage
Southern Gardening

Bachman's Heritage Cottage

Monday, November 25, 2019 - 7:00am
Hot Ornamental Peppers
Southern Gardening

Hot Ornamental Peppers

Sunday, September 8, 2019 - 7:30am
Planting a Salad Table
Southern Gardening

Planting a Salad Table

Sunday, August 4, 2019 - 4:45pm
Okra
Southern Gardening

Okra

Sunday, November 4, 2018 - 2:00am
Sharpening Your Tools
Southern Gardening

Sharpening Your Tools

Sunday, March 11, 2018 - 5:00am

Listen

Tuesday, October 1, 2019 - 7:00am
Friday, September 20, 2019 - 7:00am
Monday, December 17, 2018 - 7:00am
Friday, October 26, 2018 - 2:00am

Contact Your County Office

Your Extension Experts

Portrait of Dr. Rick Snyder
Extension/Research Professor
Greenhouse Tomatoes and other vegetables, Field Vegetables, Mushrooms