Nutrients, What Does Nitrogen Do for My Lawn?

Nitrogen, the most abundant element in the air comprising of 78%, which is 3.7 times more than the percentage of oxygen. Crazy to think about the amount of Nitrogen around us and yet we still have to fertilize our lawns with it. Why doesn’t it get pulled from the atmosphere during rain events? In short, it does but only after thunderstorms because it has to get changed from a gas into a nitrate which the plant is able to uptake. That’s why grass is always greener after a lightning storm. It’s not the rain, it’s the electrical charge in the air changing nitrogen form to an available type for turf. Maybe there is a concept for an invention here!

Growth

Nitrogen is a macronutrient that is the main growth regulator for turfgrass and is the one of main elements used in the forms of Nitrate and Ammonium. It has a function in chlorophyll production (photosynthesis and greening effect), and the formation nucleic acids, proteins, enzymes and amino acids (shoot growth and leaf development). In abundance it can have a negative effect on grass (growing too much) and in scarcity it has a negative effect (growing too little, not recovering from damage and lower photosynthetic ability).

Obtaining the right amount for our grass is crucial and should be one of the first steps to developing a successful DIY program. Nitrogen should be applied at times of the year where growth is favorable for the grass and not at times when lower temps are predicted going into winter months. In Scotland we would say, “Spring High N, Summer Low N, Autumn No N just minors”. Warm season grasses have different requirements as seasonal growth is greater, but the same principals apply where you don’t want to apply large amounts of nitrogen before colder weather.

How Much Nitrogen Does My Grass Need?

Obviously, this depends on a soil test but a standard program for cool season turf would look like the following:

Grass Type (Cool Season)	Annual Nitrogen Requirement, lbs. per Acre
Kentucky Bluegrass	3 – 5
Black Beauty Tall Fescue	2 – 3
Perennial Ryegrass	3 – 5
Creeping Bentgrass	2 – 4

Grass Type (Warm Season)	Monthly Nitrogen Requirements lbs. per Acre (Active Growing Months)
Bermudagrass	0.5 – 1.5
Centipedegrass	0.1 – 0.3
Paspalumn	0.5 – 1
St. Augustine	0.5 – 1
Zoysiagrass	0.5 – 1
Bahiagrass	0.1 – 0.5

When Should I Fertilize

Cool Season

Plan on 4 application per year, spread out across the growing season. Sure, you can do less but if you are reading this, I assume you want to do it right but not overdo it. This is for synthetic fertilizer applications, not organic. Organic fertilizer mostly relies on microbial breakdown, synthetic doesn’t. Please read post on Organic Fertilizers.

First App in spring after first flush of growth has reduced. Time this with your preemergent application for crabgrass in April/May. Try to apply about 1 to 1.5 lbs. of N at this time and expect this to feed your lawn for about 4 weeks. Make sure Nitrogen release is in a faster formulation like Ammonium Sulphate and Urea. On every bag of fertilizer there is a guaranteed analysis that details minimum quantities of NPK and the formulation of each. Check this to see what kind of release the fertilizer has.

Second App after 4 to 6 weeks when you start to see slowed growth apply another 1 -1.5 lbs. of the same type of release fertilizer.

Third App before the height of summer and Nitrogen excess is not what we want. Plan on apply 0.5 – 1 lb. of a slow-release product that will give you 8 to 12 weeks of release like a Sulfur Coated Urea, Polymer Coated Urea, Methylene Urea that will give you about 0.05 – 0.1lb release per week.

Then your fourth app should be after you aerify, I aerify after Labor Day here in Chicago when temps are heading down, and I am not worried about lack of rainfall.

Apply another 1 – 1.5 lbs. of N at this time to last you going into the fall months. This can be part quick and part slow-release fertilizer. Quick for recovery from summer stresses and aerification and slow to give it a constant feed going into fall and by the time you get to winter months most of the Nitrogen has been used.

Warm Season Grasses

An organic program is somewhat easier to design in this climate due to the average warmer temperatures throughout the year but for now we will stick with a synthetic fertilizer program.

I don’t know about you, but I would rather minimize the frequency I am fertilizing my warm season lawn. If I can get away with 4 applications that last 3 months each, then that’s the way I want to do it. Depending on your location you need to calculate active growing periods for your lawn and grass type at the time of year. Overseeded lawns will require different applications due to the development of new grass. Ultimately, evaluate growing times for each species and apply the specified amount of Nitrogen when the species is actively growing.

Slow-release fertilizers can last long with the longest being of the Polymer Coated Urea’s which can release up to 270 days. This source will generally provide a consistent feed over extended periods and is available further coated with preemergent. If you split your program into 4 applications, then for bermudagrass you will want to apply enough N to release at a rate of 0.5 – 1.5 lbs. of N per month.

Excessive Nitrogen

Excessive Nitrogen can cause a major headache for the avid lawn DIYer and has a negative effect on the environment through leaching. Without knowing it you have created a myriad of problems that can turn your lawn ugly pretty quick. High nitrogen leads to excessive growth, the 1/3rd mowing rule goes out the window leading to you needing to mow more frequently or scalp your lawn down. Scalping your lawn by removing more than 1/3rd at a time actually increases shoot growth leading to another increase in mowing frequency. If not kept up accordingly, the lawn will surely deteriorate, become patchy and you will feel deflated.

Additionally, excess Nitrogen reduces rooting, carbohydrate formation, disease resistance, recuperative capacity and vigor.