Liquid lawn fertilizer applied with hose-end sprayer

What Happens to Grass After Fertilization?

After fertilization, grass experiences several physiological responses contributing to its growth and overall health.

Fertilizing Grass and Nutrient Uptake

Grass roots absorb the nutrients from the fertilizer applied to the soil. These nutrients primarily include nitrogen (N), phosphorus (P), and potassium (K), along with other essential micronutrients, depending on the fertilizer composition. Once applied, granular fertilizers require an additional breakdown by rain or irrigation to convert into liquid form. Liquid fertilizers require water to move downward into the root zone, which makes the liquid solutions absorbable by the grass roots. 


close-up photo of grass and roots in soil


Grass roots are equipped with numerous tiny root hairs, extensions of the root's epidermal cells, which significantly increase the surface area available for nutrient absorption. The tips of the roots, which are constantly growing and exploring new soil areas, are the primary sites for absorbing nutrients and water.

The soil's nutrients are dissolved in water, forming a solution that contains essential nutrients in ionic form, such as nitrate, ammonium, phosphate, potassium, calcium, and magnesium. Soil particles, mainly clay and organic matter, hold cations (positively charged ions) on their surfaces. Grass roots can exchange hydrogen ions from their root hairs for these nutrient cations, a process known as cation exchange. Nutrients move from areas of high concentration in the soil solution to areas of lower concentration near the root surface by diffusion, a process that's passive and driven by the concentration gradient. As plants transpire, they draw water from the soil into their roots. This water movement, known as mass flow, carries dissolved nutrients, delivering them to the root surface.  

For nutrients present in lower concentrations, grass roots use active transport mechanisms. This involves using energy (ATP) to move nutrients against their concentration gradient through protein carriers in the root cell membranes. Many grasses form symbiotic relationships with mycorrhizal fungi, which extend the root system through their hyphae, increasing the soil volume explored and enhancing the uptake of nutrients, especially phosphorus.

Specific ion channels and carrier proteins in the root cell membranes facilitate the uptake of various nutrients. Once inside the root cells, nutrients are transported to different parts of the plant via the xylem, which distributes water and dissolved nutrients from the roots to the leaves and other tissues.

The Benefits: What Does Fertilizer Do?

Plant Growth: Nitrogen promotes leaf and stem growth, resulting in a lush, green appearance, and fertilizer application can promote rapid growth, helping grass fill in bare spots and recover from thinning, which is particularly important after events like heavy foot traffic, pest infestations, or drought that can leave the lawn looking sparse.

Color Enhancement: Grass often exhibits a more vibrant, greener color following fertilization, especially if nitrogen is included in the fertilizer formulation. This improved coloration enhances the aesthetic appeal of the lawn or turf area. Nitrogen is a critical component of chlorophyll, the pigment responsible for the green color of grass. Adequate nitrogen levels increase chlorophyll production, resulting in a deeper green color. Nitrogen is also essential for synthesizing amino acids, the building blocks of proteins vital for cell growth and development. Healthy, vigorous growth contributes to a lush, green appearance.


close-up of green grass


Density and Thickness: As nutrients become available, grass blades grow thicker and denser, leading to a more uniform and robust turf canopy. Fertilizer enhances grass density by supplying essential nutrients that promote vigorous growth and strong roots. Adequate nitrogen levels produce rapid, robust shoot growth, making the grass thicker and denser by stimulating the production of tillers (side shoots), which increase the number of grass blades per unit area and enhance overall density.


Root Development: Adequate nutrient supply from fertilization promotes healthy root growth, resulting in more robust and deeper root systems that improve the grass's ability to withstand environmental stresses such as drought and disease. Phosphorus plays a crucial role in energy transfer within the plant by forming ATP (adenosine triphosphate), which is necessary for various metabolic processes, including growth and maintenance.


Phosphorus, essential for root growth, promotes strong root development, enhancing the grass's ability to absorb water and nutrients efficiently, which in turn supports vibrant top growth and color, as well as recovery and regrowth after damage.


Plant Vigor: Potassium helps regulate the opening and closing of stomata, which are pores on the leaf surface that control water loss and gas exchange. Proper water regulation is crucial for maintaining cellular turgor and supporting growth. Potassium activates enzymes involved in photosynthesis and other metabolic processes, promoting efficient growth and development. A lawn that is struggling from a macronutrient deficiency can become more susceptible to other environmental stressors. 


Recovery from Damage: Fertilization can aid in the recovery of grass from damage and promotes quicker regrowth and repair of affected areas. Fertilizer helps the grass recover by providing essential nutrients that support repair and regrowth processes, strengthening the plant's ability to overcome stress and damage. Elements like iron (Fe), manganese (Mn), and zinc (Zn) play roles in various physiological functions that support stress resistance and recovery.


 Infographic for the function of nitrogen, phosphorus, and potassium


Nitrogen, vital for synthesizing amino acids and proteins for cell repair and growth, aids in the rapid regeneration of new tissue after damage from mowing, foot traffic, or pests. Phosphorus supports root development and energy transfer within the plant, with strong roots enhancing the grass's ability to absorb water and nutrients, which is critical for recovery.


Potassium improves grass's overall health and resilience, aiding recovery from stress and damage by regulating water uptake and activating enzymes involved in growth and repair processes.  A balanced fertilizer ensures that grass receives all the essential nutrients in the correct proportions, preventing deficiencies that could hinder recovery. Balanced nutrition supports overall plant health and resilience. 


16-4-8 NPK lawn fertilizer on green grass


Supporting Photosynthesis: Nutrient-rich grass leaves can conduct photosynthesis more efficiently, producing and storing energy that supports growth and development. Adequate levels of nutrients, particularly nitrogen and magnesium (a chlorophyll component), enhance grass's photosynthetic capacity. Increased photosynthesis produces more energy, essential for repairing damaged cells and promoting new growth. 


What Happens to Grass during Over-fertilization?

Apply fertilizers correctly, following the label’s recommended rates and timing, to avoid over-fertilization, which can lead to nutrient imbalances, environmental pollution, and other negative consequences. Additionally, incorporating fertilization into a comprehensive lawn care program that includes proper watering, mowing, and pest management practices helps ensure optimal turfgrass health and performance.


infographic on steps to prevent over-fertilization


What is fertilizer burn?

Fertilizer burn on turfgrass occurs when fertilizer is applied improperly or excessively, damaging the grass. Too much fertilizer can overwhelm the grass with nutrients, causing imbalance and stress. The excess salts in the fertilizer can draw water out of the grass through osmosis, dehydrating and damaging the plant tissue. Uneven distribution of fertilizer across the lawn can result in some areas receiving less fertilizer while others receive less, which can lead to localized burning in areas with excessive fertilizer.


Fertilizers with high nitrogen content, particularly quick-release nitrogen sources, can increase the risk of fertilizer burn. Nitrogen promotes lush, rapid growth, but excessive amounts can stress the grass and make it more susceptible to burn. Applying fertilizer during drought or dry weather can exacerbate the risk of fertilizer burn as, without adequate moisture, the grass may struggle to absorb and process the nutrients efficiently, leading to burn symptoms.


High temperatures can increase the likelihood of fertilizer burn as heat accelerates the metabolic processes in plants, making them more susceptible to damage from excess salts in the soil. Compacted or poorly draining soils can exacerbate fertilizer burn by trapping salts near the surface, where they can directly contact the grass roots. Some grass species or cultivars are more sensitive to fertilizer burn than others. For example, fine-textured grasses like Kentucky bluegrass and perennial ryegrass are more prone to burn than coarse-textured grasses like tall fescue.


The Key to an Effective Fertilizer Program

Fertilizing your grass leads to numerous benefits that enhance its growth, vigor, and resilience. Proper nutrient uptake through roots, supported by mechanisms like cation exchange and mycorrhizal associations, ensures that essential elements like nitrogen, phosphorus, and potassium are effectively utilized. These nutrients contribute to vibrant color, increased density, robust root development, and overall plant vigor. However, it's crucial to apply fertilizers correctly to avoid issues like fertilizer burn and nutrient imbalances. By incorporating fertilization into a comprehensive lawn care program that includes proper watering, mowing, and pest management, you can maintain a lush, healthy, and attractive turfgrass.


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