Sodium bicarbonate, commonly known as baking soda, is frequently promoted as a natural solution for various lawn and garden issues, often suggested as a mild fungicide or a homemade spot weed killer. Given its widespread use and alkaline nature, many homeowners wonder about its safety when applied to turfgrass. Whether baking soda is bad for grass depends entirely on the concentration and method of application, as improper use can easily damage or kill a lawn.
How Baking Soda Chemically Affects Turf
The primary danger of using baking soda on a lawn stems from its nature as a salt, specifically a sodium salt. When applied heavily or in concentrated amounts, the sodium component rapidly increases the salt concentration in the soil and on the grass blades, leading to a condition called salinity stress. This high concentration of soluble salts outside the grass roots and cells draws water out of the plant tissue through osmosis, essentially causing the grass to dehydrate. The turfgrass, unable to absorb necessary moisture, experiences severe cellular water loss, resulting in a chemical burn.
The second mechanism of damage relates to the alkalinity of sodium bicarbonate, which has an approximate pH of 8 in solution. A concentrated mixture can rapidly spike the soil’s pH level beyond the tolerance range for most turfgrass varieties. This sudden increase in alkalinity disrupts the balance required for nutrient availability. When the pH is too high, grass roots struggle to absorb essential micronutrients like iron and manganese, hindering growth. Sodium ions can also negatively affect soil structure, especially in clay soils, reducing water infiltration.
Recognizing Symptoms of Sodium Bicarbonate Damage
Damage from a concentrated application of baking soda is typically visible and occurs quickly, often within hours or a day of application. The initial sign is usually a rapid yellowing of the grass blades, a symptom known as chlorosis, indicating a sudden inability to produce chlorophyll. This is quickly followed by browning or scorching, particularly at the leaf tips and edges, which signifies dehydration and tissue death caused by the salt burn.
In severe cases, where a heavy dusting or concentrated liquid was applied, the grass will turn dark brown or even black in localized patches. These areas often appear circular or follow the specific pattern of the application, such as a spill or heavy spot-treatment. The damage is non-selective, affecting desirable turfgrass just as effectively as the targeted weed or fungus. Immediate intervention is required to prevent permanent loss.
Best Practices for Targeted Use and Recovery
If an accidental spill or overly concentrated application has occurred, the most immediate step for recovery is to flush the affected area heavily with water. This process, known as leaching, aims to move the excess sodium salts down and out of the root zone, reducing the high concentration that is drawing moisture from the grass. The area should be soaked repeatedly over several hours or days to dilute and wash away the baking soda residue.
For areas experiencing prolonged high-sodium stress, applying a soil amendment containing soluble calcium, such as gypsum, can aid in the recovery process. Calcium ions have a stronger electrical charge than sodium, allowing them to displace the sodium from the soil’s cation exchange sites, helping to restore soil structure and nutrient balance.
To use baking soda to target issues like powdery mildew, it must be applied in highly dilute solutions. A common recommendation for a fungicide spray is to mix one tablespoon of sodium bicarbonate with one gallon of water, often including a few drops of dish soap to help the solution adhere to the leaf surface. This mixture should only be applied as a light mist directly to the affected foliage, avoiding soil saturation. It should never be used as a broadcast treatment across the entire lawn.