Clover is a common cover crop and forage plant valued for improving soil health and fertility. The productivity of this legume is highly sensitive to soil chemistry, specifically the level of acidity or alkalinity (pH). Understanding clover’s soil pH preference is fundamental for successful growth, especially when establishing a new lawn or pasture. The correct pH dictates the plant’s well-being and the functioning of the beneficial microorganisms it relies upon.
Clover’s Optimal Soil pH Range
Clover performs best in soil that is slightly acidic to neutral, typically within a pH range of 6.0 to 7.0. Maintaining this narrow window is important because a deviation significantly reduces the plant’s vigor and yield. Growth becomes noticeably inhibited when the soil pH drops below 5.5.
Highly acidic conditions cause nutrient deficiency and toxicity. Essential nutrients like phosphorus, calcium, and magnesium are significantly reduced in availability. Conversely, the solubility of aluminum and manganese increases sharply, leading to toxic levels that stunt root growth and impair nutrient absorption.
Different varieties of clover have varying tolerances, but all prefer the neutral range. White Clover and Red Clover perform best when the soil pH is 6.5 or higher. Weak, stunted growth and a pale green color are often the first signs that the soil is too acidic.
How Soil Acidity Disrupts Nitrogen Fixation
Clover’s sensitivity to acidity stems from the disruption of its symbiotic relationship with soil bacteria. Like other legumes, clover relies on a partnership with specific Rhizobium bacteria for nitrogen fixation. These bacteria live within specialized structures called nodules that form on the clover’s root system.
The viability and function of these nitrogen-fixing bacteria are severely compromised in acidic soil. When the pH falls below approximately 5.8, bacterial populations decline, and their ability to colonize roots and form new nodules is greatly reduced. Without functioning nodules, the clover cannot convert atmospheric nitrogen into a usable form, resulting in nitrogen deficiency.
A secondary issue involves the trace element molybdenum, a cofactor in the nitrogenase enzyme used by Rhizobium to fix nitrogen. Molybdenum’s availability decreases as the pH drops. Acidic soil thus harms the bacteria directly and limits the supply of a necessary component for nitrogen fixation. This ensures the clover remains nitrogen-starved, leading to poor health.
Testing and Adjusting Soil pH for Clover Health
The first step in ensuring a healthy clover stand is accurately measuring the current soil acidity. While home test kits provide a quick estimate, a professional soil sample analysis offers a more precise measurement. A lab analysis provides the exact pH and nutrient deficiencies, allowing for a targeted approach to soil correction.
If the soil test shows a pH below the ideal 6.0 to 7.0 range, agricultural lime is applied to neutralize the acidity. Lime is typically composed of calcium carbonate or dolomitic lime, which also supplies magnesium. The amount of lime needed is determined by the soil’s current pH and its buffer capacity (resistance to pH change).
Raising soil pH is a slow process, as lime gradually dissolves over several months. Therefore, lime should be applied well in advance of planting clover, ideally in the fall or winter for a spring planting. Regular soil testing every few years is the best way to monitor the pH level and ensure the soil remains optimal.