Fertilizing plants, lawns, trees and flowers. Gardener in gloves holds white fertilizer balls on background of green grass

Fertilizer For New Grass Seed: When to Apply and What to Use

By Britt Olizarowicz

If you have just planted a new lawn, you may be curious about the benefits of fertilization. Taking the time to fertilize new grass will ensure that you have a healthy and established lawn long term. In our guide to fertilizer for new grass seed, we provide:

  • The benefits of fertilizer for new grass seed
  • How to apply fertilizer to new grass seed
  • And options for both DIY and professional seeding and fertilization

What is Lawn Fertilizer?

Lawn fertilizer is a nutrient solution for your grass that will help it grow greener and stronger. Lawn fertilizer can be applied via a spreader or with a spray solution, and there are many different types of lawn fertilizer.

The main nutrient makeup of fertilizer is Nitrogen, Phosphorus, and Potassium. Nitrogen helps grass grow faster, Phosphorus improves root growth, and Potassium helps in the time of drought.

The best nutrient makeup for your lawn will depend on the type of grass that you have, its age, and its current condition.

Why New Grass Seed Should be Fertilized

New grass is vulnerable. As the new seeds have just germinated, they are subject to issues with weakness, brownout, and lawn pests. You should be fertilizing new grass seed twice before it is put in the ground and four to six weeks after it is established.

The key to fertilization is to do a soil test first and ensure that you use the proper fertilizer ratio. Blindly fertilizing the lawn creates issues that could end up burning out the new lawn or causing it too much stress.

If you fertilize a new lawn properly, it can help with root growth and coloration, two things a new lawn can struggle with. The stronger you can make the new grass, the lower the chance of the grass having long-term health and nutrient issues.

Will Fertilizer Kill New Grass

Fertilizer can kill new grass, but it shouldn’t. If you put down a new lawn and decide the next week that you want to add quick-release nitrogen to speed things up, you may do some damage. Ensuring that you don’t kill your new grass means paying attention to the timing, type, and application rate of fertilizer.

When New Grass Seed Should be Fertilized

There are two times to fertilize new grass. The first is with a lawn starter fertilizer before the start of planting. The second is with a regular lawn fertilizer four to six weeks after the lawn is established.

One of the most important steps in this process is to do the soil test on the grass first. This soil test before planting grass seed lets you see where you stand and what changes need to be made to get the area to where it needs to be.

How Soon Can Fertilizer be Applied to New Grass Seed?

The first application of fertilization after planting new grass seed should be about 4 to 6 weeks after the seeds germinate. Once you have already cut the lawn because the grass reached the proper height and you can see that it is growing strong and is overall quite healthy.

How Often New Grass Seed Should be Fertilized

It’s best to use the lawn starter fertilizer before putting your grass seed down and then another fertilizer about six weeks after the lawn germinates. Once you use that second fertilizer, it’s best to leave the turf alone for some time and let it work things out.

Overfertilizing a new lawn could end up causing stress and creating brown spots and other issues. The best way to avoid this is to do the initial fertilization and then wait a solid eight to twelve weeks before you fertilize again.

Before fertilizing again, do another soil test so that the proper fertilizer is chosen. Also, pay close attention to other issues in the turf and climate/weather before you decide to fertilize. If this eight-week mark puts you in the fall season, that can be one of the best times to fertilize before the winter.

What is the Best Fertilizer for New Grass Seed

The best fertilizer for starting the new lawn is a high phosphorus quick-release fertilizer. However, once the seed is established and you are ready for your first fertilization post-germination, a slow release with a higher nitrogen count is the best option.

Understanding the different types of fertilizer for new grass seed can ensure that you have a green lawn without bare spots.

Types of Fertilizer For New Grass Seed Application

Homeowners have two options for fertilizer for new grass seed applications: slow-release and quick-release fertilizers. If you are not careful about the timing of the application of these fertilizers, the existing lawn and any new grass could be in trouble.

Slow-Release vs. Quick-Release Fertilizer

A slow-release fertilizer will stay in the soil for many weeks. Over time the fertilizer will work to keep the lawn healthy and green as the Nitrogen, Phosphorous, and Potassium are released into the root system. With the slow-release fertilizer, there is a much lower chance of burnout and overfertilization as just a small amount is released at a time. Slow-release fertilizer also promotes strong root development. This is considered a regular fertilizer.

The quick-release fertilizer is a starter fertilizer. This is placed in an area where the new grass seed will be planted. The NPK ratio of the starter fertilizer is typically a bit higher in Phosphorous. Quick-release fertilizers bring a strong hit of nutrients, sometimes too strong for the wrong grass type.

Homeowners that plant a new lawn need to be very careful about herbicides inside a fertilizer. Both cool season grass and warm season grass that is newly planted will struggle with weed killer as it will work against the new seed. Keep your soil moist, hand pull weeds, and properly prep the area if you want to prevent things like crabgrass and other invasive weeds.

  • Regular / Slow-Release Fertilizers
    • Pros
      • Lower chance of burning the new lawn
      • It can help improve the overall strength of the turf
      • Options for all types of grass, including bluegrass, zoysia, tall fescue, ryegrass, and more
      • Will green up the lawn in a few weeks
      • Works with both new sod and grass seedlings
    • Cons
      • It can take longer to work than a quick release
  • Starter / Quick-Release
    • Pros
      • The right option for starting a new lawn
      • It can sometimes be combined with a crabgrass preventer before starting the new lawn
      • Quick results
    • Cons
      • It should not be applied to a newly established lawn
      • Incorrect fertilizer application can lead to landscaping issues and grass dying

How to Apply Fertilizer to New Grass

Now that you have a better idea of what fertilizer can do for your new lawn and whether or not this is positive, it’s time to take a look at the best way to apply fertilizer to a new lawn. For this process, we are going to start at the beginning as there are two opportunities for fertilization that need to be addressed.

Step 1: Test Soil and Prepare Area for Planting

When you have decided on the area of your lawn where you want to plant new turf, you must first test the soil and prepare the area for planting. This soil test is simple to do and can be done at a local garden center. Take a look at where your soil stands and what amendments it may need. Most turf can use a little dolomite lime to help get it where it needs to be.

Step 2: Apply Starter Fertilizer

Once you have tested the soil, raked it out, and removed any existing weeds or old turf, you can then apply a starter fertilizer. Remember, the starter fertilizer is a quick-release option that is applied with a broadcast spreader before planting the seed. Once this is in place, you can start seeding your new lawn.

Step 3: Plant Grass

Once you have applied the starter fertilizer, it’s time to plant your grass seed. Use our guide for how to plant grass seed to help you understand this process, how to make sure you apply enough seed per sq. ft., and much more.

Step 4: Maintain and Mow

After a few weeks, you should be starting to see your grass grow and become stronger. At this point, you will want to watch water application rates and be sure that you are carefully watering the lawn with what it needs. In addition, wait until the grass reaches optimal mowing height and ensure that you give it its first cut.

Step 5: Apply Slow Release Fertilizer

We recommend doing another soil test before the final fertilizer application. If you can, check the weather to ensure that you will not apply the fertilizer right before a large storm. The runoff of the fertilizer into other areas of the lawn or out into the street is not a good thing.

Slow-release fertilizer like Scotts TurfBuilder is a great option as long as no herbicides are included in the product.

Step 6: Monitor and Reapply

The last step in this process is to monitor your new grass and reapply fertilizer if necessary. Many times overseeding, aeration, and reapplication of fertilizer are needed in the fall, especially the first year you plant your new lawn. Continue to take soil tests and ensure that there are no other amendments to the soil that could help your grass grow.

DIY vs. Professional Lawn Care

Now that you have a basic idea of what goes into the fertilization process for new grass seed, you may be wondering if this is something you would like to do or if it’s best to hire a professional. There are positives and negatives to both sides here.

Lawn fertilization takes a bit of planning. You must know how many square feet of turf you have, and you must have a way to purchase the products you need and apply them. This can take some time and a bit of understanding of NPK ratios.

A professional lawn care service like TruGreen will come to your home, give a free estimate and determine exactly what needs to be done. The process of working with TruGreen is incredibly easy, and with more than 15 years in the industry, they know exactly what your issues are with having to complete this process on your own.

Best Overall

  • Large variety of plan options tailored to homeowners wants and needs
  • All services are backed and performed by TruExpert℠ Certified Specialists
  • Services provided in 49 states

Final Thoughts

We hope you can now understand this process of fertilization for new grass. The key takeaway here is that fertilizer will not kill your new grass; you must be smart about approaching this process. Do not put a quick-release fertilizer down just after planting, and don’t overdo it with the wrong ratio by not being smart about NPK formulas. If you do a little research and follow the proper steps, you will see very few issues with this process.

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