Fertilizer labels warn, “Apply nitrogen when turf is actively growing.” Why?

Why is the “Apply nitrogen when turf is actively growing” disclaimer so important? 

There is a disclaimer that is found on most, if not all, fertilizers containing nitrogen.  Have you noticed?  “Apply nitrogen when turf is actively growing.” Let’s talk about why this disclaimer is on the bag and what it means.

The first of the three numbers on all bags of fertilizers is nitrogen; the next two are phosphorus and potassium (aka N-P-K).  If there is a number greater than 0 in the first position, then that means that Nitrogen is included at the percentage represented by the number. Nitrogen is the fuel for plant growth and essential to plant health.  However, it can also be deleterious to plants and the environment if used inappropriately. 

Let’s start with, “How do you know your turf is actively growing?”  The obvious answer is when you are having to mow your turf.  Dormant is the term used when the grass is not actively growing. 

For warm and cool season grass owners, your grass will go dormant when the temperatures consistently drop and cause the soil temperature to also drop. Depending on your USDA growing zone, you can expect your warm season grasses to go dormant anywhere from end of October to December and come out around end of February to April. And for all the cool season grass owners, your grass will go dormant approximately in November and come out around March.

The reason you do not apply nitrogen when turf is not actively growing is because nitrogen is a fuel for growth.  You don’t want to initiate growth while the grass is naturally hibernating for winter.  The nitrogen will also not get absorbed by the plants during dormancy and wash off into the watersheds and be released as greenhouse gasses into the atmosphere.  The overuse of nitrogen could potentially harm the plant and cause nutrient excess in the environment.

As a recap, nitrogen is a vital growth stimulant and safe when used at the right levels at the right time.  Also be sure to perform lab-based soil tests so you know the right levels of nitrogen for your crop species  — but only when the crop is actively growing!