How to Change Soil pH in South Carolina

Quick Guide to Changing Soil pH in South Carolina

Soil pH Range: 0 to 14, with 7 considered neutral
Acidic Soil: Below pH 7
Alkaline Soil: Above pH 7
Best pH for Acid-Loving Plants: pH 5.0 to 5.5
Best pH for Most Vegetables & Ornamentals: pH 5.8 to 6.5.
Common Ways to Raise Soil pH: Agricultural limestone, wood ashes
Common Ways to Lower Soil pH: Elemental sulfur, aluminum sulfate
Most Important Step: Always test the soil before adjusting the pH

Understanding Soil pH and Plant Growth

Soil pH directly affects nutrient availability, plant health, and overall garden performance.

How Soil pH Affects Nutrient Availability

Soil pH is a measure of soil acidity or alkalinity.

The pH scale ranges from 0 to 14, with 7 considered neutral. Values below 7 indicate acidic soil, and values above 7 indicate alkaline soil.

Soil pH is among the most important environmental factors affecting plant growth because it directly influences nutrient availability. Plants thrive best in different soil pH ranges.

Best Soil pH Ranges for Garden Plants

Acid-loving plants (pH 5.0 to 5.5): Azaleas, rhododendrons, blueberries and conifers

Slightly acidic soil plants (pH 5.8 to 6.5): Vegetables, grasses and most ornamentals

Soil pH values outside these ranges may result in reduced plant vigor and nutrient deficiencies.

How Soil pH Affects Nutrient Availability

Maintaining the proper soil pH helps plants absorb essential nutrients more efficiently.

Nutrients for healthy plant growth are divided into three categories: primary, secondary and micronutrients.

Primary Plant Nutrients (Macronutrients)

• Nitrogen (N)
• Phosphorus (P)
• Potassium (K)

Primary nutrients are needed in greater quantities than other plant nutrients.

Secondary Plant Nutrients

• Calcium (Ca)
• Magnesium (Mg)
• Sulfur (S)

Secondary nutrients are required in lesser quantities by plants, but are no less essential for healthy growth than the primary nutrients.

Micronutrients in Soil

• Zinc (Zn)
• Manganese (Mn)

Plants require micronutrients in very small amounts.

Most secondary and micronutrient deficiencies can be easily corrected by maintaining soil pH at optimal levels.

Soil pH Chart for Nutrient Availability

Nutrient availability changes significantly as soil pH becomes more acidic or alkaline.

The major impact that extremes in pH have on plant growth is related to the availability of plant nutrients or the soil concentration of plant-toxic minerals.

In highly acidic soils, aluminum and manganese can become more available and more toxic to the plant. Also, at low pH values, calcium, phosphorus and magnesium are less available to the plant.

At pH values above 6.5, phosphorus and most micronutrients become less available.

Factors Affecting Soil pH in South Carolina

Several factors influence soil pH.

Parent Material and Soil Formation

The pH value of a soil is influenced by the kinds of parent materials from which the soil was formed. Soils developed from basic rocks generally have higher pH values than those formed from acid rocks.

How Rainfall Changes Soil pH

Rainfall also affects soil pH. Water passing through the soil leaches basic nutrients, such as calcium and magnesium. They are replaced by acidic elements such as aluminum and iron.

For this reason, soils formed under high rainfall conditions are more acidic than those formed under arid (dry) conditions.

Fertilizers and Organic Matter That Affect Soil pH

The application of fertilizers containing ammonium or urea accelerates acidification.

Organic matter decomposition and some organic mulches, such as pine needles and oak leaves, can slightly increase soil acidity.

Soil Buffering Capacity and Soil Texture

Buffering capacity is the rate at which soils resist pH change and varies among soil types.

Sandy soils are generally less resistant to pH change than clayey soils.

Clayey soils have a higher buffering capacity, as do soils with a high organic matter content.

This means that to raise or lower the pH of clayey soils, more soil amendments are needed than for sandy soils.

Increasing Soil pH in South Carolina

Soil pH in South Carolina is typically acidic, and liming materials are often used to raise it for improved plant growth.

Why South Carolina Soils Are Often Acidic

South Carolina soils are typically acidic (pH 4.5–6.0), but this should not be assumed without testing.

To make soils less acidic, the common practice is to apply a lime-containing material. Ground agricultural limestone is most frequently used.

The finer the limestone particles, the more rapidly it becomes effective.

Different soil types will require different amounts of lime to adjust soil pH.

The soil texture, organic matter content, and the plants to be grown are all factors to consider when adjusting the pH. For example, soils low in clay require less lime to achieve the same pH change as soils high in clay.

Choosing the Best Lime Material for Soil pH Adjustment

Homeowners can choose from four types of ground limestone products to raise soil pH: pulverized, granular, pelletized and hydrated.

Pulverized Lime

• Finely ground
• Fast reaction

Granular and Pelletized Lime

• Less likely to clog fertilizer spreaders
• Easier turf application
• Convenient for lawns

Hydrated Lime

Hydrated lime should be used with caution because it neutralizes soil acidity more rapidly than regular limestone.

When to Apply Lime to Soil

Soil test results and the recommended pH range for specific plants should determine lime needs. For more information on soil testing, refer to Soil Testing (HGIC 1652).

Soil samples should be taken in the fall for the succeeding year’s garden.

If test results indicate a need for limestone, it can be applied in the fall or winter months. Generally, for best results, limestone should be applied two to three months before planting to allow time for it to neutralize the acidity.

Use the Clemson Lime Rate Calculator to determine precise application rates based on soil test results.

Best Practices for Lime Placement and Soil Incorporation

Lime placement is the most important factor in its effectiveness.

• Maximum lime contact with the soil is essential.
• Lime reacts slowly in dry soil.
• Moisture is essential for lime reaction
• Incorporation improves effectiveness.
• Lawn lime is typically surface applied.

Using Wood Ashes to Raise Soil pH

Wood ashes can be used to raise the soil pH.

Benefits of Wood Ashes

• Contains potassium and calcium
• Adds phosphate, boron, and other elements
• Can gradually raise soil pH

Precautions When Using Wood Ashes

• Can raise soil pH significantly in sandy soils
• Avoid contact with germinating seedlings
• Avoid contact with plant roots
• Apply a thin layer in winter and incorporate it in spring
• Test soil annually
• Avoid excessive application

Why Coal Ashes Should Not Be Used

Coal ash has no lime value and may be acidic, depending on the source.

Decreasing the Soil pH for Acid-Loving Plants

Some ornamental and fruit plants require acidic soil conditions and may develop nutrient deficiencies in alkaline soils.

Plants That Grow Best in Acidic Soil

• Blueberries
• Acid-loving ornamentals
• Other plants prone to iron chlorosis

These species develop iron chlorosis when grown in alkaline soils.

How to Recognize Iron Chlorosis in Plants

• Yellowing leaves
• Similar in appearance to nitrogen deficiency
• Common in alkaline soils

Improve iron chlorosis by lowering soil pH.

Best Materials for Lowering Soil pH

Two materials commonly used to lower soil pH are aluminum sulfate and sulfur.

Using Elemental Sulfur to Lower Soil pH

• Sulfur works gradually
• Soil bacteria convert sulfur into sulfuric acid
• Soil moisture affects conversion speed
• Soil temperature affects conversion speed
• Finely ground sulfur reacts faster
• Conversion rate can be slow and take several months

Using Aluminum Sulfate to Lower Soil pH

Aluminum sulfate lowers soil pH immediately after dissolving in the soil.

• Excessive applications may injure roots
• Aluminum accumulation may occur
• Follow soil test recommendations
• Avoid repeated applications without retesting

Comparing Sulfur and Aluminum Sulfate for Soil Acidification

Elemental sulfur

• Gradual pH reduction
• Requires soil bacterial activity
• Slower results
• Often preferred for long-term adjustment

Aluminum sulfate

• Rapid pH reduction
• Immediate reaction
• Greater risk of overapplication injury
• Requires careful application

How to Apply Soil Acidifying Materials Safely

• Work into the soil after application
• Wash materials off foliage immediately
• Avoid overapplication
• Use caution on lawns

Soil Amendment Application Rate Tables

The following tables provide general amendment rates for adjusting soil pH in loamy soils.

• The rates are in pounds per 10 square feet for a loamy soil.
• Reduce the rate by one-third for sandy soils
• Increase the rate by one-half for clayey soils

Aluminum Sulfate Application Rates for Lowering Soil pH

Use this table to estimate aluminum sulfate application rates for lowering soil pH in loamy soils.

Present pH	Desired pH
	6.5	6.0	5.5	5.0	4.5
8.0	1.8	2.4	3.3	4.2	4.8
7.5	1.2	2.1	2.7	3.6	4.2
7.0	0.6	1.2	2.1	3.0	3.6
6.5		0.6	1.5	2.4	2.7
6.0			0.6	1.5	2.1

(Pounds per 10 square feet)

Sulfur Application Rates for Lowering Soil pH

Use this table to estimate sulfur application rates for lowering soil pH in loamy soils.

Present pH	Desired pH
	6.5	6.0	5.5	5.0	4.5
8.0	0.3	0.4	0.5	0.6	0.7
7.5	0.2	0.3	0.4	0.5	0.6
7.0	0.1	0.2	0.3	0.4	0.5
6.5		0.1	0.2	0.3	0.4
6.0			0.1	0.2	0.3

(Pounds per 10 square feet)

Use the Clemson Soil Acidification Calculator for precise sulfur or aluminum sulfate application rates based on soil test results.

Key Takeaways for Managing Soil pH in South Carolina

• Always test soil before adjusting pH
• Most South Carolina soils are naturally acidic
• Lime raises soil pH
• Sulfur lowers soil pH
• Soil texture affects amendment needs
• Retest soil periodically

Originally published 06/99