8/1/2024 - By John Keeler

After a long summer of stress, your cool season turfgrass might need a little fertility boost heading into fall. Late-season fertilization must not be confused with dormant or winter fertilization.

Late-season fertility promotes root development, enhances carbohydrate reserves, and extends color retention in cool-season turf. The benefits of late fall nitrogen will be seen next spring and summer with earlier green-up, improved turf density, and improved tolerance to spring diseases such as red thread and pink patch.

“Physiologically, fall is one of those times that a plant is sort of in the sweet spot because the weather conditions are optimal for the plant to be most efficient with those nutrients,” notes Cale Bigelow, Ph.D., professor of agronomy at Purdue University.

Fall Fertilizer – How to Choose the Best Options

The number of fertilizer choices you have is staggering. Most options involve organic, sulfur-coated, or poly-sulfur-coated products, some form of methylene urea, and polymer-coated urea.

Fall Fertilizer - Organic Fertilizer

Natural organic fertilizers are typically derived from by-products of plant and animal processing industries. The nitrogen release rates vary quite a bit among products since the release of nitrogen is dependent on soil microbes and environmental conditions like soil temperature, moisture, and pH, which all affect the release of natural organic fertilizers. Organic fertilizer would be a viable choice for a dormant feed application.

Fall Fertilizer - Sulfur-Coated Products

Sulfur-coated or poly-sulfur-coated products are made by spraying urea prills or granules with molten sulfur. A sealant, such as wax or a mixture of oil and polyethylene, is often applied to seal pores and imperfections in the sulfur. This is important because it is those imperfections that absorb moisture and break the sulfur coating releasing 100% of the nitrogen. This would be a good choice for quick recovery.

Fall Fertilizer - Methylene Urea Products

Urea-formaldehyde fertilizers, also known as methylene urea products, are widely used in turfgrass as slow-release sources of nitrogen. There are three categories of methylene urea:

Cold water-soluble

The cold water-soluble portion provides readily available nitrogen in the first 2-4 weeks.

Water-soluble

The water-soluble portion is predictable in terms of release and provide 4-12 weeks of fertility.

And water insoluble

The water-insoluble is the least predictable and releases significantly slower than quick release, granting fertility to your turf within 1-3 years.

A good blend of cold-release, water-soluble, and water-insoluble is what you should be looking for. Any methylene urea product that does not claim water-insoluble nitrogen as a percentage of the total nitrogen, will release nitrogen quickly.

Fall Fertilizer - Polymer-Coated Urea

Polymer-coated urea (that’s right, POLYON®) is a completely different product than any other slow-release product on the market, and it is the polymer coating process that sets POLYON controlled-release fertilizer apart from the rest. The reactive layer coating and superior bonding properties applied in this process are repeated until the desired coating thickness is satisfied. The result is a very uniform coating on the urea particle.

Different coating thicknesses are used to obtain different nitrogen release rates, the thicker the coating, the slower the release of nitrogen. Nitrogen release increases with higher temperatures and is less dependent on soil moisture levels, soil pH, or microbial activity, in comparison to other fertilizers on the market. Depending on the coating thickness and application rate, POLYON can release nutrients for up to 18 weeks and will even pause its release through dormancy to give your turf nutrients right when the turf and temperatures warm up.

When to Apply Fall Fertilizer

Now that you have chosen a fertilizer source, when is the best time to apply? For slow-release nitrogen products, September or October will be your window. This will help build carbohydrate reserves in your plants, and the roots will still be growing at the same time as the shoot growth has slowed, thus allowing roots to take full advantage of the fertilizer application. For quick-releasing fertilizer, most people feel this application should take place when shoot growth has stopped, but the grass is still green, and the ground is not frozen. Take note that this timing can vary from year to year and location to location. So, be flexible.

Let us not forget the importance of a little potassium in your blend. Potassium (K) promotes winter hardiness, disease resistance, and wear tolerance in turf. A half pound of Nitrogen (N) and Potassium (K) just before dormancy is ideal.

For Fall Fertilizer, Contact Your Harrell’s Rep

For more information on fall fertility, your fertilizer options, when you should apply, benefits, etc., reach out to your local Harrell's Representative. They are your best resource for product knowledge and any other questions you may have related to your turf. If you would like to learn more about POLYON controlled-release fertilizer, check out this video of Dr. Jeff Atkinson walking through how POLYON works.