You have to feed your lawn. Well, maybe you don't have to … BUT if you want good growth and healthy plants, you want to provide adequate nutrition for all those tender little friends out there. Proper nutrition is as important for our lawn as it is for us, and just like our own diet (or lack thereof) we can get our lawn into trouble by underfeeding or overfeeding it. Underfeeding weakens the turf; and a weak, thin turf allows weeds to become established. Overfeeding gives lush, soft growth that is an open invitation for diseases and insects to wreak havoc. Providing the right amount of food for the grass plants is not all that difficult if you follow a few simple rules.


Let's begin with nitrogen, the engine of plant growth. In the normal course of its growing cycle, grass uses more nitrogen than any other substance. From a practical standpoint, this means that gardeners apply more nitrogen and spend more money on it than on any other fertilizer. By understanding how it works and what it does, you can save money and get better grass performance.

Nitrogen is a vital part of most growth processes in grass plants. Chlorophyll depends largely on nitrogen for its existence and operation in producing carbohydrates to support the grass plant. Amino acids and proteins for plant growth depend on adequate amounts of nitrogen as well, as do the enzymes that transport the vitamins, which also depend on nitrogen within the plant. In short, if a grass part or function does not need nitrogen directly as part of its building-block or functioning system, it does require nitrogen indirectly as part of the process by which it was constructed. Nitrogen is a basic building block in this grass playground.

Symptoms of Nitrogen Deficiency or Overfeeding

If the grass does not have the right amount of nitrogen for growth or maintenance, there are serious disruptions in the plant life cycle. The first symptom that you'd see in an underfed lawn is a yellowing of the grass plants—and subsequent yellowing of the lawn. The lawn loses its deep green sheen and starts to look sickly and pale, or chlorotic, due to a lack of chlorophyll. The second symptom is that the lawn growth rate will slow down. The grass will not grow as quickly, even though the time of year indicates it should be sending all kinds of growth skyward. If you save your clippings or rake a predetermined area of grass after every mowing, you'll quickly see any decrease or increase in the amount of clippings produced. A decrease in clippings may reflect the lack of available nitrogen.


This rule states: “You only have to feed your plants if you want flowers, fruit, or growth.” Remember that lawns are composed of thousands of individual grass plants. If you want them to grow, you have to feed them.

Another less visible change in the grass as a result of insufficient nitrogen is reduced root growth. Grass that lacks chlorophyll is producing fewer carbohydrates. This reduction in carbohydrates (energy) limits the ability of the roots to grow and regenerate. So, if the tops look sickly and light green to yellowish, you can bet that the roots are equally unhappy.

Does this mean that a gardener should just load the nitrogen right to the lawn and the problems will be over? Nope. It doesn't work that way. If you overload nitrogen onto the lawn, several things might happen. To begin with, if you really overload it, nitrogen will burn the existing grass plants and they'll die. If you don't go that far but you give the plant more than it needs to eat, it will get fat. You can probably imagine people as fat, but can you imagine a fat grass plant? Try this thought. If you overfeed your lawn with nitrogen, each individual grass plant will grow so quickly it will develop a thin outer cell layer (the cuticle for you scientific types). This layer of cells is responsible for keeping bacteria and other pathogens out of the plant; when it is thin and weak from overfeeding, it does a poor job of guarding the gates—keeping diseases out of the grass plant. Thin cuticles equal plants that are ripe for diseases and pest infestations. Also, excess nitrogen stimulates the grass plant to produce more aboveground shoots than the roots can support. The grass looks good, but disease, insects, and poor root growth wait just around the corner. This is particularly a problem in the spring when gardeners overfeed their lawns. Initially, the lawn looks good, but the weak grass has problems with disease and insects during early and midsummer.

The solution, as in many things, is to find the correct balance for feeding nitrogen. Not too little and not too much.

Sources of Nitrogen

The advertisements for lawn fertilizers are truly confusing. The manufacturers try to convince you that one form of nitrogen is better for your plants than another or that an organic source is more readily available to your plants than a chemical source. You've heard or read these kinds of ads. Here's the basic information about the kinds of nitrogen found in the packages and what this means to you as a homeowner.

Inorganic sources of nitrogen are rarely found in fertilizers meant for the home trade. Compounds such as ammonium nitrate, ammonium sulfate, and potassium nitrate can easily burn the grass if applied even slightly over the recommended rates. These chemicals also absorb moisture from the air; if left in an open bag, they would form clumps and become unusable. If you see a bag of fertilizer with an inorganic source of nitrogen listed on the label, do not buy it. It may be cheaper than other fertilizer products; but if you make a mistake and burn your grass, the cost is much greater than the cost of a good bag of fertilizer.

You will see other kinds of nitrogen advertised. Each company is trying to sell you a product based on one of two criteria: the excellence of its product or the cost. Unfortunately, you can't have it both ways in the nitrogen business. These are the basic products you'll find as the source of nitrogen in most bagged fertilizers. I'll start with the most expensive and work to the cheapest.

1. IBDU (Isobutyledenediurea). This is a mouthful of a name, but it does have some useful characteristics. To begin with, IBDU is relatively insoluble with cold water. This means that when you apply it to your garden, it will not decompose immediately and give the plants a flush of food. IBDU decomposes slowly and is available to the grass plants over a long period. As a result of the manufacturing process, each molecule of this product is the same size and contains 32 percent nitrogen. This uniformity creates a product that is easy to work with and brings no surprises for the homeowner. Fertilizer manufacturers combine these molecules into different-size particles (more molecules for larger particles) so the particles will break down at different times in order to feed the lawn over a long period of time.


  • Leaves turn a yellow or yellow-green color.

  • Older leaves die quickly and new shoots are pale green.

  • Plants are stunted in growth and do not grow quickly.

  • Diseases such as dollar spot, rusts, and red thread are more prevalent.

  • Turf is thinner, not as luxuriant. There is increased weed competition.

  • Some grass may go reddish or reddish purple in color, particularly in cool weather.

IBDU is the most expensive product because of its uniformity and method of manufacture. It also has some disadvantages depending on the weather. IBDU releases its product quite slowly. If it is the only source of fertilizer you use, there will be a time lag between application and availability to the plants, perhaps as long as two to three weeks. If you see IBDU in the analysis on the label, you'll often see urea added as well to increase the speed of its availability to the plants. Also, if you live in a cool area, you'll find that the breakdown rate of this product is slow; cool temperatures slow down the breakdown process. However, cool spells do not bother IBDU as much as other slow-release forms, so it is often the fertilizer of choice in cool spring areas. Also, if there is no water to dissolve the nitrogen particles, then the fertilizer will not be available to the plants. Dry springs with no irrigation can leave the fertilizer sitting on the lawn waiting for the proper conditions to dissolve.

2. Sulfur-Coated Urea (SCU). This product is one of the most commonly found ingredients in lawn fertilizer bags. It is about one-third cheaper to produce than IBDU and does the same job. The urea or nitrogen source is sprayed with molten sulfur and formed into little “prills,” or tiny beads. When the sulfur hardens, the encapsulated urea is safely enclosed in an almost waterproof coating. To prevent these particles from sticking together, manufacturers will add a silica such as diatomaceous earth to the product, which allows each individual bead to resist clumping in the bag. As you might imagine, the thickness of the sulfur coat determines how fast or slow the urea is made available to the grass plants as food. Different manufacturers will advertise their products as having different lengths of time over which they will feed your lawn and will try to convince you that their product is the best on the market. Each bag will have a wide mix of different-size beads to enable the fertilizer to make itself available to the lawn plants over a predetermined period.

The release of SCU is determined by temperature (the higher the temperature, the faster it releases), available water (the wetter, the faster) and the health of the lawn. The overall health of the lawn determines how many micro-organisms are present. The more micro-organisms that are available to assist the sulfur to decompose, the faster the SCU will be made available to the grass plants. In other words, the healthier your lawn, the better the SCU will work. Of course, remember that the fastest way to increase the number of micro-organisms in any soil is to add compost.

3. Urea. Urea is the fastest acting nitrogen source found in home lawn fertilizer bags. It is also the cheapest to produce, making it tremendously popular with manufacturers. Urea is almost completely available as you apply it to your lawn, so the turf will have an almost overnight response to the fertilizer.

This has several important consequences. First, if you overapply urea, you will burn your lawn with the excess nitrogen. The grass will die and you'll have to replace it with a renovation program. Second, irrigation or rainfall will quickly dissolve urea and leach it down through the soil, carrying it away from the grass root zone. Urea's normal active working life in the garden is measured in days or a week or two depending on moisture conditions.

Urea is not available to plants when the soil temperatures are cold. If you apply it too early in the spring before the grass has started to grow actively, it will likely be dissolved and leached out before the grass roots can make use of it. So, if the majority of the nitrogen in the bag is urea, apply it carefully after the grass has started to grow actively.


Phosphorus is necessary to the growth systems that move and store energy within the plant; if the amounts of phosphorus are limited, so are the growth rates. It is also a primary component of the plant cell membrane, both in the leaf and in the root. Its role in root growth is well known throughout the gardening world. Just as it is important to flowering plants and trees, phosphorus is important to grass plants for root establishment. Seed development also depends on phosphorus since DNA contains phosphorus. So if the grass species you are growing spreads by seed, having adequate phosphorus available is a good tactic for maintaining a thick lawn.


  • Do not add a bit extra to help the grass grow faster. This only creates problems with nitrogen overfeeding.

  • Follow the directions for spreading fertilizer. Be prepared to give the lawn more frequent, but smaller, feedings during the growing season.

There is some research to show that adding phosphorus to the soil reduces disease attacks on turfgrass, although the research is not consistent on this point. It very well may be that soils lacking in phosphorus invite diseases to attack grass plants, and that bringing the phosphorus levels up to optimum levels reduces the diseases that can attack the grass plant. In any case, having enough phosphorus in the soil is a good idea.

Symptoms of Phosphorus Deficiency

The first symptom of phosphorus deficiency is that the grass blades turn a dark, green color. This is not the color of healthy grass. It is much darker—a sickly green shade rather than a healthy green shade. Another way of describing it would be to say that there are purple tones in the green. Do not confuse this with cold injury that occurs in the fall when the soil temperatures start to plummet. Luckily for both of us, phosphorus deficiency is a rare event in the home lawn. There is normally more than enough phosphorus present for all lawn needs.

Secondary symptoms are much less noticeable and do not respond quickly to fertilizer application. Phosphorus deficiency lowers the grass's resistance to diseases and negatively affects its resistance to heat stress, drought, and its overwintering ability in cold climates. Unlike a nitrogen deficiency when improvements can be seen overnight, phosphorus deficiencies are not so quickly remedied or clearly identified.

Symptoms of Phosphorus Overdose

On the positive side of the coin, the interesting fact is that grass plants do not react to overdoses of phosphorus in the same way they react to overdoses of nitrogen (by dying). In fact, they hardly react at all to extremely high levels so the major problem is economic. I remember getting a soil test back for a lawn area and seeing extremely high levels of phosphorus in the result. It was a pleasure to find out I could save money for several years by not applying any phosphorus. You will simply waste your money if you apply too much phosphorus to your lawn, but you will have a hard time finding any negative health symptoms on the grass plants.

A second consequence (after your excess spending) of excess levels is that annual bluegrass will become established on your lawn. It loves high levels of phosphorus. If you want to grow this weed species, feed high phosphorus levels.

A third concern is pollution. Excess levels of phosphorus are associated with high algae levels in natural water areas. Although most of this comes from big users and producers of phosphorus such as golf courses and livestock farms, urban lawn owners cannot escape some responsibility. If the fertilizer spreader puts any prills (tiny beads) onto the street, they will be washed down into storm drains and local watercourses. If the lawn is next to water areas, as in cottages and camps, then spreading and careless handling can lead to runoff or fertilizer landing into or next to the water area. Reducing pollution is everyone's responsibility.


Potassium is not found in any of the important cell constituents of grass plants. It is not found in cell walls, proteins, or chlorophyll. Although this may, on the surface, suggest that it is not as important as the other major plant nutrients, nothing could be further from the truth. Think of potassium as the gasoline that drives the grass growth engine. You don't find gasoline inside the walls of the engine, but without it, you can't drive very far. Plant scientists name a substance that performs this kind of activity a cofactor. Potassium has to be present for just about everything in the grass plant to work properly and is consumed in these processes but it is not used as a building block by the grass plant. Another way that potassium is used as an energy source is in opening and closing the stomata, or sweat glands. Found mostly on the underside of the leaves, stomata must open and close to allow the plant to sweat—and that takes energy. Potassium is involved in this process. Without it, the plant is not as efficient at opening and closing the stomata.

This leads us into the deficiency symptoms for potassium, and quite frankly, this is a problem. Unlike nitrogen with its very visible symptoms and phosphorus with its subtle but still distinct symptoms, potassium does not have a clearly or easily seen deficiency symptom. The grass doesn't grow as well as healthy grass. It is stressed because it cannot use its stomata efficiently; it is more prone to diseases and insects but it appears to be green healthy grass.

Older fertilizer blends tended to have lower potassium levels because turf scientists could not identify exactly what role it played. Now, even if they cannot pinpoint the exact functions of potassium, they understand its overall importance and fertilizer content reflects this importance. Older nutrient formulas might have been something like 35-10-10 or 25-5-5. Now the bags will have a higher third number. The percentage of potassium is usually higher than that of phosphorus, so the bags will read 35-15-30 or 25-5-15.

Minor Trace Nutrients

Sometimes, if grass is pale green and not growing very well, you'll be told to add micronutrients to the lawn. The quick answer to this is “yes and no”—it all depends on the micronutrient being recommended. If the grass is pale green, you should first add nitrogen to the lawn. If this does not cure the problem within 24 hours, then your lawn probably has a micronutrient problem. Let's examine the most common problems and their cures.


Reading a fertilizer label is covered in more detail on page 26, but the most important thing to understand is the way the three major fertilizer elements are listed. The three numbers prominently displayed on every label represent the percentage of that element in the mix. So a 35-10-15 analysis would represent 35 percent nitrogen, 10 percent phosphorus, and 15 percent potassium. After you total the percentages of fertilizer, any leftover amounts are composed of fillers.


The absence of this micronutrient is most likely to cause yellowing of the grass. Iron is one of the main components of chlorophyll (the substance that makes the grass “green”), so if it is absent, there will be reduction in chlorophyll and a yellowing of the grass leaf. Iron is rarely deficient in soils that have a pH lower than 7.0. It can happen but it is quite rare. When the soil pH is above 7.0, the iron changes its form to one that is not as readily available to the plant. This is when we see the problem. You have two possible options if you suspect iron deficiency. You can send a soil sample to the extension services and wait a month for the results. Or, you can go to a good garden center, buy a bottle of fertilizer or micronutrient product that contains iron, and apply it to a small section of the lawn. Iron-deficient grass is very responsive to iron; you'll see a change within 24 hours if this is the problem.

Iron is usually sprayed onto the grass leaves to be directly absorbed by the plant. If you apply it to the soil as a powder, because of the soil pH that caused the problem in the first place, the iron will quickly change into the unavailable form. So if you have a choice at the garden center shelves, pick the spray. If your grass turns dark green overnight, you know that iron was the problem, and you also know that your soil is too basic (pH higher than 7.0). A long-term solution is to lower the soil pH, or make your soil more acidic.


If the nitrogen and iron treatments have not worked to darken the lawn, your grass may be lacking magnesium. This micronutrient might be to blame when the soil is acidic or if there is a high proportion of sand in the soil. Acidic soils have a chemistry that prevents the magnesium ion from attaching itself to the cations; this is a fancy way of saying that the plants can't absorb the magnesium. Adding magnesium makes it more available to the plant. But the long-term solution is to increase the pH of the soil, so there is room for the magnesium to get into the soil chemical mix. Sandy soil has the wrong electrical charges to attract and hold magnesium so it becomes deficient. Adding magnesium is a short-term, but effective, method of solving sandy soil deficiencies.

Luckily, we don't have to go far to obtain some magnesium: get out the Epsom salts. If you want to run a small test, mix a teaspoon of Epsom salts into a pint of warm water. Shake the mixture to dissolve the salts and then spray it on a small section of turf. It won't take much to turn the grass green if there's not enough magnesium, so only lightly spray the grass leaves. If the spray starts to run off the leaves, you are applying too much. Spray a little less so there is no runoff. If the grass greens up overnight or within 24 hours, magnesium deficiency is the culprit. Apply Epsom salts at the rate of 1 pound per 1,000 square feet of lawn. The easiest way is to mix this amount of salts into 3 or 4 gallons of warm water and apply the mix through a hand sprayer. Don't overapply the magnesium. A single pound per 1,000 square feet is enough to cure the problem.


Golf course turf managers routinely spray iron onto the fairways in the fall when the temperatures start dropping. Nitrogen (particularly urea forms) becomes inactive when soil temperatures drop, and the grass cannot absorb it. A spray of iron helps hold the green color and the player's peace of mind.


I've seen TV advertisements touting the existence of sulfur in fertilizer as a wonder drug for the lawn. Well, maybe … Sulfur deficiencies will indeed cause a chlorosis or yellowing of the grass, but for the majority of lawns in North America, sulfur is not the culprit. I have seen reports that suggest that much of the continent receives between 10 and 15 pounds of sulfur per acre per year from rain. Only in areas where the rain comes directly from the sea (such as the West Coast) will sulfur deficiencies be a real problem. Having said that, sometimes, depending on the soil, sulfur will be the immediate cure for lawn yellowing.

Other Micronutrients

There are a variety of other micronutrients that rarely create problems because of their universal availability in soils. Some, such as boron, can create problems if there is an excess. For example, applying boron to the soil is the recommendation for controlling creeping charlie. If the gardener gets too enthusiastic about applying boron, the grass also might stop growing. This is why staying within recommended guidelines is so important. Chlorine, particularly from swimming pools, is always a concern for homeowners. At this point, I've never seen a report of chlorine damage from swimming pool water. The levels of chlorine are usually too low to hurt turf. If you can swim in it, the grass will not be bothered.

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