Of the 16 essential nutrients grass requires to grow healthy and vibrant, nitrogen is one of the biggest – and certainly the most talked about and obsessed over. Nitrogen is the N in NPK.
Table of Contents
- What is Nitrogen and Why is it Important for Lawns?
- Where Does Nitrogen In Soil Come From?
- Can Your Lawn Have Too Much Nitrogen?
- What Are Signs Of High Nitrogen Levels In Grass?
- How Do You Fix High Nitrogen Levels In Grass?
- How Can I Grow A Healthy Lawn With Less Nitrogen Fertilizer?
- Forget the “perfect lawn”; a healthy lawn is quality turfgrass even if it’s not as dark green.
- Identify Your Grass Species and Variety.
- Leave Grass Clippings on the Lawn to Recycle Nitrogen.
- Overseed with Nitrogen-Fixing Legumes Like White Clover and Microclover.
- Use Natural Sources with a High Proportion of Insoluble Nitrogen.
- If You Use Inorganic Sources, Measure Your Lawn and Apply Only 1 Pound Per 1,000 sq ft of Nitrogen in One Application.
- What are Some Signs of Nitrogen Deficiency in Grass?
- How Do You Fix Nitrogen Deficiency in Your Lawn?
- What Are The Best Sources of Nitrogen For Your Lawn?
What is Nitrogen and Why is it Important for Lawns?
Nitrogen helps a plant grow new leaves. For lawns, along with being necessary for the grass to live, nitrogen allows grass to grow thick and green.
More than that, nitrogen is an essential part of:
- Amino acids, which every protein and enzyme a plant produces needs,
- Chlorophyll, which gives grass their green color and helps plants absorb sunlight for photosynthesis,
- Embedded in DNA, and
- Alkaloids, a protective secondary compound.
It’s also necessary for soil microbes to live. Beneficial microbes have many benefits to offer your lawn, including:
- Break down organic matter into nutrients usable by plants,
- Recycle and regulate carbon, nitrogen, and phosphorus,
- Fix atmospheric nitrogen into nitrates (the usable form of nitrogen),
- Improve soil structure and stability, and
- Help control diseases.
The usable form of nitrogen, nitrates, is water soluble. Rainfall and irrigation carry nitrates away from the soil, especially in sandy soils. Between leaching and how many species require nitrogen to live, you will probably need to replace nitrogen every year.
Where Does Nitrogen In Soil Come From?
All nitrogen, whether it’s in natural sources or manufactured, originates in the atmosphere. Nitrogen (N2) comprises 78% of the atmosphere. But plants can’t absorb N2. It needs to be converted to nitrate (NO3).
Atmospheric nitrogen becomes fixed in the soil through nitrogen-fixing bacteria, through lightning and rain, and through the fertilizer manufacturing process. Fertilizers commonly use ammonium nitrate (NH4N03) or other water soluble nitrates. Nitrogen-fixing plants (like clover) form special relationships with nitrogen-fixing bacteria to fix nitrate in root nodes. The stored nitrate releases into the soil upon decomposition.
Organic sources of nitrates come from mineralization, when plant or animal matter decomposes to ammonia (NH3) and reacts with water to form ammonium (NH4). Bacteria convert the ammonium to nitrites (NO2), which other bacteria convert into usable nitrate (NO3).
Can Your Lawn Have Too Much Nitrogen?
Yes, your lawn can have too much nitrogen – and you will see the results quickly. Nitrogen toxicity happens when more nitrogen than your grass needs floods the soil, causing the tips of the grass blades to “burn” or turn brown. Excess soluble salts (like in quick-release nitrogen formulas) will burn the roots. As the toxicity progresses, the grassblade turns pale yellow (chlorosis) because the excess nitrogen prevents the uptake of other nutrients, then dies.
But even without nitrogen burn, using more nitrogen than your grass need causes you a lot more work for a poorer quality turfgrass:
- Increased mowing. The excess nitrogen causes the grass to grow faster than it would otherwise. The faster your grass grows, the more you need to mow!
- Increased thatch. The faster your grass grows, the more thatch builds up, especially with species that are spread by stolons. Stolons take longer than other plant parts to break down. The more plant matter that needs to decompose, the longer it takes for it to decompose, the more thatch will build up.
- More leaves without the root structure to support the growth. Leaf growth outpaces root growth, meaning that your grass doesn’t have a stable foundation from which to grow. Shallow roots mean needing to water more often, the grass being more prone to heat, cold, and disease stress, and the grass accesses fewer nutrients on its own.
- Burns out soil microbes in a boom and bust cycle. Soil microbes feed on nitrogen and when you add high amounts of nitrogen to the soil (especially in quick release formulas), the soil microbes gorge and reproduce rapidly. The nitrogen is used up quickly and the soil microbes die, leaving only a scant portion of its original population behind.
- Reduces a lawn’s tolerance to high and low temperatures.
- Attract insect pests and disease. Unsustainable growth leads to poorer health, which attracts insects and disease.
- Leeches away and pollutes groundwater. Nitrogen is very water soluble. That’s why we need to apply it every year – if the plants don’t take it up, then rain (and irrigation) carry it away. Along with phosphorus, nitrogen runoff causes algae blooms in local waterways, which end up smelling terribly and killing off aquatic life.
What Are Signs Of High Nitrogen Levels In Grass?
- Signs appear within days of fertilizer application
- Grass grows quicker than usual
- Grass with brown, “burnt” tips
- Stripes or patches of brown, green, and yellow grass (if fertilizer was applied unevenly)
- Straw-coloured patches (usually caused by animal urine)
- Grass has turned brown and crunchy, and the roots are black or mushy (end stage; death)
How Do You Fix High Nitrogen Levels In Grass?
If you’ve added too much soluble nitrogen, and your grass is still alive, then water the affected patch with 1 inch of water (the water reaches one inch deep into the soil) as soon as you notice the problem. Continue to water 1 inch a day for the next week.
Shallow waterings are key! The excess salts will sink deeper into the soil without leaching into groundwater or running off into storm drains and waterways.
If your lawn has died, then you’ll need to start a new lawn from scratch.
How Can I Grow A Healthy Lawn With Less Nitrogen Fertilizer?
Forget the “perfect lawn”; a healthy lawn is quality turfgrass even if it’s not as dark green.
Forget the dark green turf that grace television and magazine ads. Those turfgrasses require a ton of money, maintenance, and care. A light or medium green lawn looks just as good with way less money and work. Our unhealthy obsession with dark green turf leads us to overusing nitrogen. You can cut back on how much nitrogen you give your lawn and still have a quality lawn.
Identify Your Grass Species and Variety.
Different species and varieties of grass require different amounts of nitrogen. Hardy grasses like Buffalograss and Blue Grama need only one pound per 1,000 sq feet per year. Popular cool-season grasses like Fescues and Perennial Ryegrass only need 2 to 3 pounds per 1,000 sq feet per year. If you have one of these grasses, but are applying enough fertilizer for Kentucky Bluegrass (4 to 5 pounds), then you’re feeding way more than is healthy for these species.
Leave Grass Clippings on the Lawn to Recycle Nitrogen.
Between 46% to 59% of fertilizer nitrogen ends up at the top of the grass – which means half of the fertilizer you apply ends up in the grass clippings you throw away! Leaving them to break down naturally on your lawn can reduce your fertilizer needs by 25% to 40%. One study even found that recycling grass clippings can contribute as much as 2 pounds of nitrogen per 1,000 sq feet!
Leaving grass clippings on the lawn doesn’t cause thatch. That’s just a myth. Fresh grass clippings decompose much quicker than dry clippings and so don’t contribute to thatch buildup.
Overseed with Nitrogen-Fixing Legumes Like White Clover and Microclover.
Legumes are nitrogen-fixers (they form a special relationship with bacteria that allows them to convert atmospheric nitrogen to a nitrate that the plant can absorb). As these nodules decompose, they release the nitrogen into the soil. If you find clover growing in your lawn, instead of reaching for herbicide or a weed puller, leave it to help your lawn. You could also overseed with clover or even start a microclover lawn.
Use Natural Sources with a High Proportion of Insoluble Nitrogen.
Soluble sources of nitrogen are just that – soluble. When it rains or when you water your lawn, the water carries the nitrogen away. The upside to soluble sources is that it’s immediately available to plants, which can be pretty handy if you have a severe nitrogen deficiency.
Insoluble is the opposite – it stays put. Unlike soluble nitrogen, insoluble nitrogen is not readily available for plants. It needs to be converted by bacteria into a usable form, but it’s less likely to burn your lawn and it stays in your soil and not in the local river. It also feeds your lawn for much longer.
Soluble sources of nitrogen to avoid include:
- Ammonium nitrate
- Ammonium sulfate
- Calcium nitrate
- Potassium nitrate
Natural/organic sources of nitrogen like compost and alfalfa meal break down into usable forms little by little. They feed your lawn over an extended period. The lower concentrations of nitrogen are ideal because you can’t accidentally cause nitrogen burn and their slow release means your lawn doesn’t grow like crazy, causing you extra work. Your lawn gets all the nitrogen it needs over months instead of weeks, and you only have to make 1 or 2 applications per year.
If You Use Inorganic Sources, Measure Your Lawn and Apply Only 1 Pound Per 1,000 sq ft of Nitrogen in One Application.
The numbers in NPK are the concentration for each nutrient. So a 10 for N means the fertilizer bag has 10% nitrogen. To get to the proper amount of fertilizer to apply, refer to a fertilizer chart. 10% nitrogen means you need to apply 10 pounds of fertilizer for 1,000 sq feet to apply 1 pound of nitrogen.
Never apply more than 1 pound of nitrogen per 1,000 sq ft in one application. To be safe, you can even try applying half the amount for one application, see how your grass reacts, and then apply the other half if it seems necessary. More than that, you will burn your lawn.
If your grass needs more than 1 pound of nitrogen, make multiple applications. This way, you don’t risk fertilizer burn, your lawn doesn’t grow out of control, and your nitrogen is more likely to end up in your grass and not in nearby waterways.
If you’re using compost, apply ¼ inch topdressing instead of doing these calculations, as that’s enough to feed your soil without covering up your grass. Depending on your grass species and soil type, you may only need to apply once a year in the late summer (warm-season) or fall (cool-season).
What are Some Signs of Nitrogen Deficiency in Grass?
Signs that your lawn has nitrogen deficiency include:
- Yellowing of grass (chlorosis), starting with older growth (lower grass blades turn yellow first as the grass recycles the nitrogen for new growth)
- Grass has reduced vigor (isn’t growing as fast)=
Iron deficiency can also cause chlorosis, where the newest growth (at the top) turns yellow or there’s a mottled yellow coloring. Pests or disease can also cause yellow grass.
The best way to confirm that your lawn is nitrogen deficient is to get a soil test! A soil test will give you a complete overview of what nutrients are present in your grass and at what levels. Knowing this will also help you find the right fertilizer to use, as too much phosphorus or too much potassium can cause severe problems that can take years to resolve (and can end up as water pollution too).
A soil test will also help you correctly diagnose whether your lawn has a nitrogen deficiency or an iron deficiency. Adding nitrogen to an iron-deficient lawn could end up forcing growth that ultimately kills your grass.
How Do You Fix Nitrogen Deficiency in Your Lawn?
- Get a soil test. If you haven’t had a recent soil test, getting one now can help you figure out if it really is nitrogen deficiency, rule out other nutritional or pH causes, and if there’s other nutrient deficiencies or excesses that you need to worry about.
- Measure your lawn to get square feet. This may seem like a tedious task (can’t you just eyeball it?), but taking this step now will save you a lot of trouble later on. You need to know exactly how many square feet your lawn is in order to apply enough nitrogen without causing fertilizer burn.
- Calculate the amount of fertilizer you need to apply. Never apply more than 1 pound of nitrogen per 1,000 square feet in one application. If your grass needs more, then make multiple applications over weeks. If you use inorganic/synthetic fertilizer, then take the concentration of nitrogen (the first number in the NPK ratio) and use a fertilizer chart to determine how many bags of fertilizer you need to apply. Divide your lawn’s square footage by 1,000 and multiply it by the pounds of fertilizer you need to apply to get the total amount of fertilizer to apply. If you use compost, then apply a ¼ inch topdressing.
- If you’re using a soluble nitrogen source, apply half to begin with and observe your lawn over the next couple weeks. If necessary, you can apply the other half. You can always add more nitrogen, but once you apply it, you can’t take it back.
- Only apply fertilizer when your grass is growing and not dormant or stressed. Applying nitrogen then will only stress out your grass more, and may end up killing it.
- If a previous fertilizer application was applied unevenly, you may find that stripes of your lawn have nitrogen deficiency while other stripes have fertilizer burn. In that case, be very careful not to apply any fertilizer to the fertilizer burn areas.
What Are The Best Sources of Nitrogen For Your Lawn?
The best sources of nitrogen for your lawn are organic/natural that feed your grass for a long time and have a high percentage of insoluble nitrogen. Grass doesn’t actually need as much NPK as lawn fertilizer bags may lead you to believe. The idea that plants need high NPK comes from agriculture, where intensively growing crops strip these nutrients out of the soil. Since we’re not farming grass, and we don’t want to mow more than we need to, lower amounts of nitrogen work just as well.
Compost & Manure Compost
Whether your compost comes from plants or animal manure, they contain quite a bit of nitrogen. The amount of nitrogen will depend on the source. Greens compost will contain between 1.5 to 3.5% nitrogen, while fresh rabbit manure has between 3 to 4.8%. Compost will also have phosphorus and potassium, and many other nutrients, so test your soil to make sure you’re not overfeeding your lawn.
Since compost contains low levels of nutrients that break down over long periods, they will not usually cause excess nutrient problems.
Alfalfa meal usually has around 3-1-2 (incidentally, this is the recommended ratio of NPK for lawns!), and also contains magnesium, iron, 16 amino acids necessary for healthy plant growth, and a naturally occurring hormone that stimulates healthy root and stem development. Cheaper alfalfa meal brands may have seeds mixed in, so try to buy higher quality products. To apply, either add cubes or pellets into the compost, or broadcast fine-milled alfalfa meal onto your lawn.
Feather meal is high in nitrogen (between 12 – 15%) which releases over 4 to 6 months. It has no phosphorus or potassium, so if you just need more nitrogen for your lawn, feather meal is a great choice.
As stated above, fresh grass clippings are an incredible and free source of nitrogen. In fact, each time you mow, the grass clippings contain between 46% to 59% of the nitrogen from a fertilizer application. By leaving them on the lawn to decompose (or adding them to your compost), you’re recycling that nitrogen back into your soil.
Nitrogen Lawn FAQs
How Often Does Grass Need Nitrogen?
How often grass needs nitrogen depends on the nitrogen source. Nitrogen is regularly depleted in the soil, so you will probably need to apply fertilizer at least once a year. Organic sources like compost and feather meal release nitrogen in small amounts over a long time, so you may only need to apply once per year. Soluble synthetic sources like ammonium nitrates leach out of the soil very quickly (polluting groundwater and nearby waterways) and so need to be applied as much as 5 or 6 times a year. It’s much better to use fertilizers with a high amount of insoluble nitrogen when possible as it remains in your soil for longer.
Does Nitrogen Help Green The Grass?
Nitrogen is the main nutrient that causes grass to be green, as it’s an essential component of chlorophyll. Problems other than nitrogen-deficiency can cause grass to lose its green color, like iron deficiency and dormancy (surviving hot or cold weather by turning brown), so it’s important to rule out these factors before applying nitrogen as it could end up hurting your grass.
Does Nitrogen Promote Root Growth In Grass?
No, nitrogen does not promote root growth in grass. Phosphorus stimulates root growth. Less frequent, deep waterings encourage grass to grow roots deeper to access more water. Too much nitrogen can force excessive growth of grass leaves, but root growth doesn’t follow, making for unhealthy grass.
Why Is My Lawn Low In Nitrogen?
There are many reasons your lawn is low in nitrogen:
- The soil is too wet, too dry, sandy, compacted, or poorly aerated.
- Grass and the beneficial microbes in the soil all require nitrogen, so they naturally deplete nitrogen over a season.
- Many synthetic sources of nitrogen are water-soluble, meaning that heavy rain or heavy irrigation can take the nitrogen right out of the soil before the grass uses it.
If you are interested in the other big fertilizer nutrients in NPK check out:
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.