What Happens When You Fertilize Your Lawn

August 15, 2020

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What Happens When You Fertilize Your Lawn

Fertilizing is critical to your lawn’s health. If you want a thick, green, vibrant lawn, there is really no replacement for proper fertilization. But a quick glance around the fertilizer aisle at your local garden store is enough to make most homeowners break into a cold sweat. The wide variety of fertilizers, along with conflicting advice about when, how, and how much to fertilize your lawn can be confusing, to say the least. But don’t let that scare you off, because skipping fertilizing will lead to a less healthy lawn. So it’s time to learn a little about fertilizer and what happens when you fertilize your lawn.

Why Your Lawn Needs Fertilizer

We all know that adding fertilizer can help your lawn green up. But why does your lawn need fertilizer at all?

The short answer is that grass needs certain nutrients to grow, and those nutrients are not always present in large enough amounts in your lawn’s soil. In some cases, the soil may simply be depleted as growing turf uses up the nutrients. However, nutrients can also be lost by leaching. Most nutrients that plants use are water-soluble, so they can be leached from the soil as rainwater or irrigation drains. Over time, this can deplete the nutrients your grass needs, but fertilizing can replace those nutrients and let your grass grow strong and healthy. If you don’t fertilize and the soil in your lawn does not provide enough nutrients, weak turf growth opens up room for weeds and pests that can damage your lawn.

What Happens When You Fertilize Your Lawn [infographic]

What Fertilizer Does For Your Lawn

Turf needs certain nutrients to grow, and fertilizer helps provide those nutrients as the soil is depleted. While dozens of minerals and nutrients play a role in your turf’s health, three nutrients make up the bulk of what your grass needs.

Nitrogen is the nutrient your grass needs the most of, and it is the one that is most likely to be depleted. Your plants use nitrogen for almost all of its internal processing, including building proteins and creating the chlorophyll necessary for photosynthesis. Untreated soil rarely provides as much nitrogen as your grass needs to thrive. Over time, nitrogen is used up and lost through leaching, so adding fertilizer with nitrogen can help maintain the nitrogen levels your turf needs.

Phosphorus is used in nearly all of your turf’s energy processes, and it is one of the most important nutrients to your turf’s overall health. However, it is required in much smaller amounts than nitrogen, so it is less likely to require large quantities from fertilizer. Phosphorus is involved in amino acid production, photosynthesis, glycolysis, and respiration. These are all crucial steps in the energy production that keeps your grass alive. While some phosphorus is necessary, it is critical to avoid over-fertilizing, since extra phosphorus that drains into waterways is considered a pollutant.

Potassium is critical to the long-term health and stability of your turf. It is required for photosynthesis and cell division, the processes through which your grass can grow. Potassium helps grass withstand drought, foot traffic, and other types of stress, and can help it stay alive over the winter months.

There are many other minerals and nutrients your grass needs and uses, but most are only required in tiny amounts that rarely need to be supplemented with fertilizer.

Understanding Fertilizer

With a little bit of knowledge about the nutrients your grass uses, it is easier to understand the types of fertilizer you will find at your local garden store. Almost all fertilizer packaging includes a series of three numbers, like 20-4-8. The numbers indicate the percentages of nitrogen, phosphorus, and potassium in the fertilizer, in that order. So a bag of fertilizer marked 20-4-8 is 20% nitrogen, 4% phosphorus, and 8% potassium. The other 68% is inert material that helps spread the nutrients.

The most important nutrient to add to your lawn is nitrogen. In almost every case, nitrogen will be the most abundant nutrient in general-use fertilizer. However, how much nitrogen you need will depend on the specifics of your lawn and its soil.

One way to determine how much nitrogen and other nutrients your lawn needs is to test the soil. Many garden stores sell test kits with instructions. Another option is to take soil to your local agricultural extension, where they can send it out for testing and provide you with results that often include recommendations for fertilizing.

How to Fertilize Your Lawn

Once you have an idea of how much nitrogen your lawn needs, you can purchase fertilizer and start to fertilize your lawn. Fertilizer comes in two types of applications: liquid and granular.

Liquid fertilizer is dissolved in water and can be sprayed onto your lawn with a liquid fertilizer applicator or an attachment to your garden hose. Liquid fertilizer has a few advantages over granulated fertilizer. First, it is usually cheaper. It can also be easy to apply over a large area. And the results are quicker than with granulated fertilizer. You may see your lawn greening up in just a few weeks. However, there are some downsides, too. Liquid fertilizer may be cheaper, but it needs to be applied more frequently. Also, because the fertilizer is more concentrated, there is a higher chance of burning your turf with too much fertilizer. Since they are water-based, there is also a higher risk of leaching if you apply too much at once. Leaching is a waste of fertilizer and a possible pollutant if the fertilizer gets into storm drains and local waterways.

Granular fertilizer is slower to take effect since it is time-released. However, the time-release also means that it is harder to damage your lawn with too much fertilizer. So while it can be a bit more expensive, granular fertilizer is often recommended for homeowners. It is easier to control, and there is a much larger margin of error. Granular fertilizer is applied with a rotary spreader or broadcast spreader. You can purchase a small hand-held spreader for under $20, while larger push spreaders can cost up to $150 or more.

Danger of Over-Fertilizing

Fertilizer can help your lawn grow full and healthy. But too much fertilizer can actually harm your lawn. Too much nitrogen can cause the blades of grass to grow faster than the roots, leading to an overall weaker plant. If you apply liquid fertilizer, too much nitrogen can damage your turf if it stays on the surface. It is always good to water your lawn after applying fertilizer to wash any residue off the grass blades and help the fertilizer soak into the soil.

Another danger of over-fertilizing is that fertilizer can wash off your lawn and drain into local waterways. Phosphorus is especially harmful since it can lead to massive algae blooms that choke off lakes and streams and make water unsafe for swimming and drinking.

If you are using a Turfgrass Group certified turf variety, you should only need minimal fertilizer. Most of our varieties need just one pound of fertilizer per 1000 square feet, split between two applications in spring and fall. So if you want to save on water and fertilizer while maintaining a beautiful lawn, try our certified varieties today. You can find a local grower here.

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