Starter fertilizer promotes the establishment of new lawns, whether from seed or sod, by providing a high concentration of phosphorus (P) for vigorous root development. Unlike regular lawn fertilizers that focus on nitrogen for leaf growth, starter products emphasize phosphate, featuring nutrient ratios like 10-18-10 or 8-32-16. Although often considered safer than high-nitrogen fertilizers, starter fertilizer can still burn a lawn. When misused, the chemical salts can injure vulnerable new seedlings and grass, making proper application techniques necessary for success.
The Chemical Reason Fertilizer Causes Burn
Fertilizer burn is directly related to the “salt index,” which measures a fertilizer’s potential to draw moisture out of plant tissues. All synthetic fertilizers are soluble salts that dissolve in soil water, increasing the solution’s concentration. When this concentration becomes too high, it creates an osmotic pressure imbalance between the soil and the plant roots.
The high salt level pulls water out of the grass roots and leaves (reverse osmosis), causing the plant cells to dehydrate. This desiccation appears as scorched, brown, or yellow discoloration on the turf. Although starter fertilizers are lower in nitrogen, they contain sufficient salts to cause damage, especially to delicate new seedlings with shallow root systems. Low soil moisture significantly aggravates this effect by concentrating the salts.
Avoiding Application Mistakes
The primary cause of fertilizer burn is over-application, resulting in an excessive concentration of salts in the soil. It is crucial to read the product label and accurately calibrate your spreader to apply the recommended rate. Applying too much starter fertilizer drastically reduces the germination rate of new seed, so never estimate the amount or use an uncalibrated spreader.
Uneven spreading is another major mistake that leads to visible burning, often resulting in distinct dark green stripes or patches of scorched grass. Granules that pile up or overlap create localized areas of high salt concentration that quickly damage the grass. To ensure uniform coverage and avoid streaking, divide the total recommended amount of fertilizer in half and apply each half in perpendicular directions across the lawn.
Applying granular fertilizer to wet grass is strongly discouraged because moisture causes granules to stick to the blades. When stuck granules dissolve, the concentrated salts burn the leaf tissue directly, creating intense burn spots. Waiting for the grass to be completely dry helps the granules fall to the soil surface where they dissolve safely.
The most important step after application is to immediately “water in” the starter fertilizer with a thorough soaking. This action dissolves the fertilizer salts and moves them into the soil profile where roots can access the nutrients. Failing to water in the product leaves salts on the surface, ready to dehydrate the grass and cause a burn, especially in hot, dry weather.
Repairing Damaged Grass
If a lawn burn has occurred, the immediate remedial action is to heavily flush the affected area with water. The goal is to dilute the high concentration of soluble salts and move them deeper into the soil, away from the grass roots. Apply water consistently for several days, soaking the area deeply for 20 to 30 minutes to wash the excess nutrients away.
Assess the extent of the damage to determine if the grass is merely stressed or actually dead. If the grass blades are brown but the crowns or roots still show white or green, the turf may recover as the salt concentration lowers. If the damaged areas are completely straw-like and dead, the spots will need to be patched. Once the soil has been flushed of excess salts, prepare the bare soil and reseed or lay new sod to repair the burned sections.