Sodium bicarbonate, commonly known as baking soda, is a household staple often considered a non-toxic alternative for various cleaning and garden tasks. It is an accessible and inexpensive option for controlling unwanted plant growth. Understanding the chemical properties of baking soda is the first step in assessing its effectiveness as a potential grass or weed killer, which depends on its application and how it interacts with plant life.
The Direct Answer: How Baking Soda Affects Grass
Yes, baking soda can kill grass and weeds, but its effectiveness is limited and non-selective. It works best on small, isolated areas of growth, such as weeds sprouting between patio pavers or in sidewalk cracks. Due to its high sodium content, baking soda is essentially a salt that causes severe dehydration in plant tissues. For large areas of turf or established lawns, using baking soda is not a practical method, as it is difficult to apply selectively and can damage desirable grass.
The visual effects on the foliage are not instantaneous; the treated plant will begin to wilt and turn brown as its cells lose moisture. Sodium bicarbonate is most effective on young, shallow-rooted weeds. Deeper-rooted grasses may only suffer damage to the above-ground foliage and often regrow from the unaffected root system, requiring repeated treatments that risk soil damage.
The Mechanism of Plant Damage
Baking soda’s herbicidal action relies on two factors: osmotic stress and a shift in soil chemistry. The immediate effect is the desiccation of the plant’s leaves and stems due to its high concentration of sodium. When sodium bicarbonate contacts the plant’s surface, the high salt concentration outside the plant cells draws water out through osmosis. This rapid loss of internal moisture disrupts cellular function and causes the leaves to burn and collapse.
A secondary effect is the change it imposes on the soil environment. Sodium bicarbonate is a mildly alkaline compound (pH about 8.3), and applying it raises the soil’s alkalinity. Since most grasses and plants prefer a slightly acidic to neutral pH, this alkaline shift disrupts the plant’s ability to absorb essential nutrients. The presence of sodium ions also interferes with the uptake of elements like calcium and magnesium, inhibiting growth.
Practical Application Methods
Two primary methods exist for applying baking soda to target unwanted grass and weeds. The dry application method involves dampening the foliage of the target plant with water to help the powder adhere. A small amount, often about one teaspoon, is then lightly sprinkled directly onto the wet leaves and stem. This technique is useful for individual weeds found in confined spaces like cracks in pavement.
Alternatively, a liquid solution can be prepared for targeted spraying, which offers better control and reduces the risk of powder blowing onto desirable plants. A common concentration is mixing 10 tablespoons of baking soda into one gallon of water. To enhance adherence, a small amount of liquid dish soap can be added. Application should occur on a dry, sunny day, as rain will quickly wash away the treatment.
Protecting Surrounding Plants
Baking soda is a non-selective agent, meaning it will damage or kill any plant it touches. The high sodium content poses a serious risk to desirable plants, so precision in application is necessary. When using a liquid spray, a physical barrier, such as cardboard or plastic sheeting, can be held around the target area to shield adjacent turf and garden plants from overspray.
A major concern is the residual effect of sodium that leaches into the soil after treatment. Excess sodium buildup reduces fertility and creates an inhospitable environment for future plant growth. This is especially true near garden beds, where runoff can carry the salt into the root zones of vegetables or ornamental plants. For large-scale weed control in a lawn, the risk of long-term soil damage outweighs the benefits of using baking soda.