Applying grass seed and fertilizer simultaneously is generally recommended for successful lawn establishment. This combined application provides immediate, localized nutrition to the seeds and emerging seedlings, promoting faster germination and robust initial growth. New grass needs instant access to the energy required to sprout and begin developing a strong root system. This method requires selecting a specialized product designed to nourish the new seed without causing damage.
The Necessity of Starter Fertilizer
Applying general-purpose lawn food alongside new seed can severely hinder establishment, requiring a specialized starter fertilizer. Unlike standard fertilizers, which focus on high nitrogen content for established leaf growth, starter blends have a different nutritional balance. New seedlings need help developing their subterranean structure before focusing on green blades above the soil surface.
Phosphorus, represented by the middle number in the NPK ratio, is particularly important. This macronutrient plays a direct role in energy transfer within the plant, stimulating cell division for strong root formation and seedling establishment. Starter fertilizers typically have a higher phosphorus concentration to support this initial root development, which is foundational for a healthy lawn.
Using a non-starter fertilizer with high nitrogen content, common for mature lawns, can result in “fertilizer burn.” Commercial fertilizers contain salts, and an excessive concentration of these salts draws moisture away from the newly sown seeds or tender roots. This process dehydrates the seedlings, causing them to turn yellow or brown and preventing successful establishment.
Key Steps for Simultaneous Application
Success with simultaneous application begins with proper soil preparation to ensure good seed-to-soil contact. Before spreading, rake the area to remove debris and lightly loosen the top layer of soil, aiding in seed embedding and nutrient absorption. Aeration or dethatching may also be necessary if the soil is heavily compacted or has a thick layer of dead organic matter.
Next, spread the grass seed evenly across the prepared area using a calibrated spreader to avoid bare patches or overcrowding. Immediately apply the starter fertilizer, using the spreader settings recommended on the product label for an accurate rate. Lightly raking the surface again after both applications helps mix the seed and fertilizer into the top quarter-inch of soil.
The most important step is the watering regimen, which must be frequent and shallow to keep the seedbed consistently moist without washing away the seed. For the first two to three weeks, water lightly two to three times daily, just enough to prevent the top layer of soil from drying out. Once seedlings emerge, gradually reduce the frequency of watering while increasing the duration, encouraging roots to grow deeper.
Critical Ingredients to Avoid
The primary substances that will negate any seeding effort are herbicides, often present in common lawn care products. Avoid any product labeled “weed and feed” or those containing pre-emergent herbicides, which prevent weed seeds from germinating. These chemicals cannot differentiate between weed seeds and grass seeds, stopping the new grass from sprouting entirely.
Similarly, post-emergent herbicides, designed to kill visible weeds, can be too harsh for fragile new grass seedlings. Applying chemicals such as 2,4-D or dicamba will likely damage or kill young sprouts establishing their root systems. It is recommended to wait until the new grass has been mowed at least two or three times before introducing any selective weed control.
Beyond herbicides, confirm that the starter fertilizer uses a controlled-release or slow-release nitrogen source, rather than a quick-release formula. While quick-release nitrogen provides immediate green-up, it poses a higher risk of fertilizer burn due to its rapid release of salts. A gentler, slow-release product ensures a steady supply of nutrients, supporting the seedling during establishment.