Many people fertilize their lawns in the spring. Is that a good idea?
Generally, lawn fertilizers contain some ratio of nitrogen, phosphorus, and/or potassium. Each element promotes plant growth in its own way. Most lawn fertilizers contain a significant amount of nitrogen. Using the hypothetical example of a 50 pound bag of 29N-0P-3K blended fertilizer, the bag contains 14.5 pounds of nitrogen, 0 pounds of phosphorus, and 1.5 pounds of potassium. Nitrogen serves as the building block of plant proteins and cell development and is essential for photosynthesis. In the absence of nitrogen, or in cases where nitrogen is not available to the plant, the plant suffers. Intuitively, adding nitrogen to a lawn in the spring seems like it would be beneficial, but don’t pull out that fertilizer just yet.
The top layer of the soil contains a combination of living and dead flora and fauna collectively known as organic matter. Organic matter plays an important role in soil water retention and nutrient cycling. By weight, organic matter is about 1%–4% nitrogen and in the stable, “organic” form, meaning organic nitrogen is not plant-available. In the spring, as the soil temperature warms, microorganisms convert the stable and unusable nitrogen into a plant-available form through a process called mineralization. The mineralized nitrogen is taken up by the plant and . . . viola! A natural spring green up has occurred.
The natural process by which nitrogen becomes available to plants in spring can be influenced by our turf management actions. Techniques such as returning (or not removing) grass clippings provides a nutrient rich mulch that over time decomposes and increases soil organic matter. Adding other amendments including composted leaf and garden waste can raise organic matter levels, too, however there’s a fine line regarding the volume of material applied. Great care should be taken not to smother the crop you’re trying to nurture with organic matter additions.
We’ve established that nature provides its own nitrogen to the plant community in the spring, but is it enough nitrogen? Do we need to help mother nature with supplemental nitrogen on our lawns? To answer that question, you need to consider your lawn type. Do you have warm season grasses (i.e., bermudagrass, zoysia grass, etc.) or do you have cool season grass (i.e., fescue, bluegrass, etc.)? For warm season grasses, which grow vigorously in the warm season, the first nitrogen application of the year should not be made until after the grass has broken dormancy and turned green, typically for South Eastern Virginia, that’s mid to late April. For cool season grasses, which grow vigorously in
the cool seasons (spring and fall), spring nitrogen applications, especially when over-applied, can lead to excessive growth as the hot and humid summer months approach. The stresses on the lawn caused by high rates of nitrogen in the spring can lead to many diseases including brown patch, gray leaf spot, and pythium blight. To be fair a lack of nitrogen can also lead to disease stresses in the form of dollar spot and rust.
It is not recommended, but if you choose to apply nitrogen fertilizer to your lawn in the spring, do so sparingly. For cool season grasses, apply no more than 0.5 lbs. of water-soluble nitrogen (WIN) per 1,000 ft² of lawn area between March 15th and April 15th, then make additional nutrient applications in the fall. For warm season grasses, apply no more than 0.5 lbs. of water-soluble nitrogen (WIN) per 1,000 ft² of lawn area after April 15th, then develop and follow a fertilization program for the remainder of the growing season.
For more detailed and site-specific information, please consider participating in the Turf Love program offered through the Colonial Soil and Water Conservation District.
Read more articles in the Spring 2024 CSWCD Newsletter.
