Ask any homeowner what their lawn needs to keep it looking healthy and green, and they will respond with 3 essential “ingredients”: water, sunlight, and nutrients.
Without a doubt, these are the most important things your lawn needs for good growth, but there’s a hidden need that is often overlooked.
Periodically you should check the soil pH to determine if your soil is acidic and if so, apply lime to bring the pH back into the proper range.
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What is soil pH?
The soil pH is a measurement of how acidic or basic/alkaline the soil is, just like the pH of liquid solutions.
pH — the potential of hydrogen — measures the concentration of positively charged hydrogen ions (H+) and negatively charged hydroxyl ions (OH-).
A higher amount of positively charged hydrogen ions creates an acidic environment; more negatively charged hydroxyl ions produce an environment that is less acidic, or basic.
Acidity/alkalinity is measured on an algorithmic scale ranging from 1- 14.
Values increase or decrease by a factor of ten when there is a change in one full unit.
- 0 – 2 is strongly acidic
- 3 – 5 is weakly acidic
- 6 – 8 is considered neutral
- 9 – 11 is weakly basic
- 12 – 14 is strongly basic
If the pH of the soil is either too acidic or too basic, the ability for plants to absorb nutrients is significantly influenced, as nutrient availability is highly influenced by soil pH.
At either end of the pH scale the plant essential macronutrients — those needed in larger amounts for plant metabolic processes — become tied up, making them difficult for the plant to absorb; the micronutrients needed become more available at these extremes, potentially becoming toxic to plants due to their abundance.
Why is liming important?
Liming is important to keep the soil pH at a level that maintains ideal nutrient availability.
Over time the soil pH can naturally drop to a more acidic level for many reasons; the addition of lime to the soil will naturally decrease the acidity, raising the pH level.
- Water movement through the soil profile from precipitation or irrigation leaches calcium cations out of the soil, leaving H+ ions behind.
- Repeated application of fertilizers replenishes nutrients depleted over time, but as nitrification occurs, H+ ions are released into the soil, increasing the soil pH.
- Plants remove essential nutrients from the soil, exuding H+ ions in exchange for the cations they are taking into their roots. As hydrogen ions increase in the soil, the pH lowers, making the environment more acidic.
Low pH affects nutrient availability.
Macro and secondary nutrients become unavailable for plant uptake (phosphorus binds to aluminum and iron oxides) and can cause deficiency symptoms.
Low pH also increases the solubility of Al, Mn, and Fe, which can create toxicity problems. High aluminum levels can slow or stop root growth.
Microbial activity is also decreased in acidic soils. This can slow down nitrogen mineralization and nitrogen fixation, the two processes vital to producing plant-available nitrogen.
A decrease in microbial activity also means the breakdown of organic material is also slowed.
What happens when you apply lime to your lawn?
According to the eXtension website, a segment of the U.S. Cooperative Extension Service, lime treats acidity by combining with carbon dioxide, water, and hydrogen ions in the soil to form free calcium ions and carbonic acid (a weak acid).
The carbonic acid molecules then break apart and form carbon dioxide gas and water. The formation of water rids the soil of hydrogen ions, increasing the soil pH.
Physical symptoms of low pH
The best way to determine if your soil pH is low is to run an analytical test that uses chemicals to measure the hydrogen ion content, giving you the pH value. Some physical symptoms will clue you into a low pH that warrants a soil test.
- Lawn moss grows more abundantly than normal turf grass(es).
- There is a surge in the incidence of weeds, diseases, or pests within your lawn.
- When you apply lawn fertilizer, there is little to no response seen in the lawn.
- The vibrant green typically in healthy blades of grass loses some of its color.
- During periods of dryness, the lawn has a lower tolerance of drought stress, and cannot bounce back as quickly or efficiently.
Testing soil pH
The most accurate way to check soil pH is to collect a soil sample and pay to have a professional soil test completed.
Soil samples can be analyzed by a local soil testing laboratory, or they can be taken to a local county extension office for testing.
For the DIY-type, you can purchase a home testing kit that will give you an approximate value or invest in a pricier soil pH probe.
To use a home testing kit, you mix soil, distilled water, and chemicals. The chemical reaction produces a color to be matched to a scale, determining the soil pH.
Ideally, you want the pH to be between 6.2 and 7 for good grass growth. If you choose to have a sample professionally tested they often give liming rate recommendations.
Tips for applying lime to your lawn
If you do need to apply lime to your lawn, dolomitic limestone and calcitic limestone are the two types of lime typically used to raise soil pH in turf.
Their chemical concentrations differ slightly from one another, but they both raise the pH.
Dolomitic limestone will also add magnesium to the soil as it breaks down; calcitic limestone will add calcium, as its name implies.
For the optimum results, and the least amount of problems, follow these tips when applying lime to your lawn.
- Run a soil test before application to determine the pH. This will help you figure out how much lime needs to be applied. Lime is typically applied at a rate of pounds per thousand square feet of turf.
- Lime is most commonly applied during the spring or fall when plants aren’t growing. Fall is best as the winter season and the freeze/thaw cycles help to break down the lime throughout the fall/winter/early spring. By the time spring comes around the soil pH will have improved.
- Aerate your lawn before lime application for better movement into the soil and root zone.
- Apply lime when you can water it into the soil well after application to remove it from the blades of grass, reducing the potential of damage.
It’s beneficial for the health of your lawn to periodically check the soil pH, and adjust it closer to neutral using lime if the soil tests as being too acidic.
Over time environmental conditions and general lawn maintenance can cause the soil pH to drop. An acidic soil decreases the nutrient availability of macro and secondary plant essential nutrients and increases the availability of micronutrients to what can be toxic levels.
Keeping the soil pH in an appropriate range keeps nutrients available for plant uptake, encouraging strong, healthy grass growth.