When to Fertilize New Grass for Best Results? Tips on Helping Your New Grass Thrive 

When seeding a brand new lawn, several questions crop up among homeowners like what’s the best time to water grass seed and when to fertilize new grass seed for best results. 

Quick Answer

I’ve always fertilized my lawn with commercial products such as lawn starter fertilizer before planting new grass seeds roughly 4 to 6 weeks after the grass seeds sprout.

However, this timeframe only works if you follow other processes such as performing a soil test and removing debris before fertilizing new grass.

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When Should I Fertilize New Grass Seed?

You should ideally apply starter fertilizer (small or large portion depending on the area) to the soil for a lush lawn before you seed or lay your turf.

You can also mix the seeds with the starter fertilizer and broadcast them over your brown turf or damaged turf areas with a rotary or drop-type spreader. 

Applying starter fertilizer after you’ve already spread grass seed can cause the nitrogen to burn the grass if not watered sufficiently. 

Since manufacturer instructions vary, refer to the lawn fertilizer label for instructions on how to use the starter fertilizer to achieve a healthy lawn environment. 

Here’s some tips from professional landscaper Dan LeSieur explaining the process of applying fertilizer on new grass seed:

Lawn Care : How Soon Can You Fertilize New Grass?

How Often to Apply Starter Fertilizer? 

Before laying down grass seed – You ideally only need 1 application of starter fertilizer before laying down grass seed.

After your grass starts to grow, you can swap the starter fertilizer with regular fertilizer and apply a second dose roughly four to six weeks later or when the grass is 1 to 1 ½ inches tall. 

In the fall – The next application of regular fertilizer for your new lawn is in the fall before the onset of frost or snow. At this time, you can use a fertilizer that’s rich in phosphorous as will promote deep root growth, and help your lawn sustain over the winter

End of winter – As part of your end of winter and early spring lawn care treatment, you can perform nitrogen fertilization to encourage fresh new growth, and reduce the risk of disease.

Things to Do Before Fertilizing New Grass 

Perhaps the most important task before fertilizing new grass is to perform a soil test to ensure that your soil isn’t lacking any critical nutrients such as nitrogen, and determine which type of fertilizer is right for your turf. Here are a few other reasons why a soil test is important.

Further, if your current turf where you plan to plant new grass seeds has weeds in it, you’ll have to improve the conditions of the area by applying a herbicide before getting started. 

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1. Perform a Soil Test 

Even though there are several expert gardeners who claim that performing a soil test is not strictly required, I beg to differ. A soil test is an important soil maintenance step that allows you to determine the pH and nutrients level of your soil. 

There are several ways to test your soil pH including with red cabbage leaves, and soil test kits and strips. 

2. Till and Remove Debris 

Dirt and debris can have an impact on new turfgrass health, so remove any sticks, dead plants, rocks, etc. from the area. Additionally, make sure the area slopes down because pools of water can cause water clogging in your lawn and cause compacted soil.

3. Amend the Soil

You can amend the soil to further aerate the soil and improve drainage by adding a 2-inch layer of organic material, such as well-rotted manure or compost. Learn a few tips on composting at home.

Amending the soil is an important step for good grass health, and using compost is a win-win situation for your yard, as it’s a natural way of improving your soil. However, you don’t want to add too much compost as a soil amendment because you risk certain problems with specific plants. 

4. Adjust the Soil pH 

A soil test will tell you if your soil is acidic or alkaline, after which you can take the necessary steps to adjust the pH accordingly. 

There are several ways to adjust pH for a healthy lawn including adding lime or sulfur as required.

  • You can apply lime if the soil pH is too low using a spreader such as a drop spreader or broadcast spreader. 

Speaking of which, you can use a spreader to spread cool-season grass or the best-adapted grass seeds and certain regular fertilizers across your entire lawn, so it’s a handy tool to have in your gardening arsenal.

5. Apply a Starter Fertilizer 

I’m going to go over starter fertilizers in more detail below and cover things such as what are starter fertilizers, the best starter fertilizers, and how starter fertilizers are beneficial for new grass growth. For now, remember to apply a starter fertilizer product after your soil is in good health. 

When to Fertilize New Grass

What is a Starter Fertilizer?

Starter fertilizers aren’t the same as regular lawn fertilizers because they have a high concentration of phosphorous as their main ingredient, and germinating grass seeds need phosphorous to build healthy, strong roots while becoming established. 

The NPK (essential nutrients) ratio of most regular fertilizers doesn’t include phosphorous due to changing regulations, making regular fertilizer bags considerably different than starter fertilizers. 

How to Choose a Good Starter Fertilizer for New Grass?

Starter fertilizers for all grass seeds and grass seedlings can be ordered in different compositions of the primary nutrients nitrogen (N), phosphorous (P-phosphate), and potassium (K-potash), which are represented by the three numbers listed on the current product label of fertilizer bags

Read my detailed article on what N-P-K means and how it affects your lawn. To explain briefly, the N-P-K ratio on a starter fertilizer, slow-release fertilizer, or even a regular fertilizer is represented by numbers, which indicate the percentage of each nutrient contained in that fertilizer bag. 

  • Nitrogen fuels plant growth and keeps your grass growing during the right season. High nitrogen fertilizer will typically have a ratio like  11 – 5 –  6
  • Phosphorous serves as the foundation and framework food for grass seeds and most other plants. Phosphorous helps is essential for all forms of growth including solid root development. 
  • Potassium offers good disease resistance, winter hardiness in turfgrass, and high tolerance to drought. 

Of all the three components, phosphorous is the most important nutrient for new grass seeds, and typical starter fertilizer with adequate nutrients including nitrogen should look like 10-10-10, 20-10-10, and 16-8-8. 

Best Fertilizer For New Grass

There are myriad different variations available in commercial starter fertilizer, so I’ve compiled a list of the most popular brands. 

Fertilizer BrandN-P-K Ratio
Scotts Turf Builder24-25-4
Greenview Starter Fertilizer10-18-10
Jonathan Green Green-Up12-18-8
Lesco Professional Starter Fertilizer18-24-12
The Andersons New Lawn Starter20-27-5
Ferti-Lome New Lawn Starter Fertilizer9-13-7
Sustane Late Summer Turf Starter4-6-4

Seedling grasses produce new tissues rapidly, therefore have higher energy and nutrition requirements, hence need greater amounts of nitrogen and phosphorous essential nutrients. 

Even though I mentioned earlier that it’s a good idea to get a soil test done to determine the deficiency of primary nutrients in your soil, phosphorous levels don’t change much over shorter periods, so you can collect soil samples as close to the date of establishment of new grass as possible. 

To make things easier, here are my top 4 starter fertilizer picks:

GreenView 2131254 Starter Fertilizer
Scotts Turf Builder Starter Food for New Grass
Jonathan Green Green Up Seeding & Sodding Lawn Fertilizer
Lesco Professional Starter Fertilizer
GreenView Starter Fertilizer 48 lb, Covers 15,000 sq. ft.
Scotts Turf Builder Starter Fertilizer for New Grass, Use When...
Jonathan Green (11540) Green-Up Lawn Food for Seeding & Sodding -...
50LB Starter Fertilizer
GreenView 2131254 Starter Fertilizer
GreenView Starter Fertilizer 48 lb, Covers 15,000 sq. ft.
Scotts Turf Builder Starter Food for New Grass
Scotts Turf Builder Starter Fertilizer for New Grass, Use When...
Jonathan Green Green Up Seeding & Sodding Lawn Fertilizer
Jonathan Green (11540) Green-Up Lawn Food for Seeding & Sodding -...
Lesco Professional Starter Fertilizer
50LB Starter Fertilizer

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Starter Fertilizer for New Grass

When to Not Use Starter Fertilizer? 

Although starter fertilizer is the go-to choice to accelerate grass seed natural growth rate, there are some situations where a one to inch layer of good quality compost amended with the soil will suffice. 

Good quality compost like bio-solids and manure-based composts provides the right dose of nitrogen and phosphorous for optimum grass seed establishment, so you don’t have to apply a starter fertilizer. Adding to this, you should refrain from using starter fertilizer in areas where you can’t control runoffs. 

Can I Use Regular Fertilizer for New Grass Seeds? 

Using regular fertilizer for new turf establishment is strongly not recommended. Regular fertilizers do not contain the amount of phosphorous needed for strong development, but generally have an NPK ratio of 1-2-1, making them suitable for mature plants. 

You also shouldn’t use starter fertilizer with mature plants, because they lack the required nutrients, which will have a big impact on turfgrass health. 

How to Apply Fertilizer to Your Newly Planted Lawn? 

Before applying fertilizer to your turf, it’s important to check the weather to ensure there’s no rain in the forecast.

A rainstorm can easily wash the fertilizer and new grass seeds away, so apply fertilizer only if there’s no chance of rain for the next two days. A slight drizzle a couple of days before fertilization is ok, but the turf should be dry before you fertilize. 

1. Calculate how much fertilizer you need 

It’s very common for homeowners to over-apply fertilizer thinking that the additional nutrients will accelerate grass growth. But applying too much fertilizer will cause the nitrogen and soil levels in your turf to increase rapidly, which can result in dead grass and damaged turf. 

You should aim to apply a starter fertilizer at the rate of 0.5 lbs to 1 pound of nitrogen per 1000 square feet.

Applying fertilizer in excess of 1.5 lbs per 1000 square feet can burn the young turf, and result in a deteriorated lawn. 

2. Water the area thoroughly 

Regardless of the grass type whether cool-season grasses or warm-season grasses, it’s time to water the area before applying lawn fertilizers to create the right moisture conditions and kickstart the germination process for a green lawn. 

Since we’re on the topic of watering, I’ll go over the three stages of watering starting from before casting grass seeds to water after spreading grass seeds to maintain the right moisture conditions. 

  1. Before spreading grass seeds – Water the area a couple of days before application where you’re going to be planting new grass seeds to a depth of 6 – 8 inches. Next, measure the depth of penetration by inserting a long stick or screwdriver into the ground about 6 – 8 inches deep and ensure that it goes down without much resistance. 
  2. After you spread grass seeds – Water the area immediately for approximately 5 – 10 minutes to gently moisten the first several inches of the soil surface. 
  3. Moving forward – You’ll want to maintain the moisture in the healthy soil days after application because if the seeds dry out, they’ll die. How often you water newly planted grass seeds boils down to the amount of rainfall your area receives after seeding. If your area doesn’t get any rainfall, water new grass seeds at least twice a day until the top couple of inches are moist. 

The best time to water grass seeds across your entire lawn is during the coolest parts of the day, which are morning and evening. During these times, the water is easily absorbed by the soil rather than evaporating during hotter temperatures. 

How to Apply Fertilizer to Newly Planted Lawn

3. Spreading fertilizer 

You can spread fertilizer by hand, but doing so will probably not result in a uniform application, and the fertilizer won’t make good soil contact in certain areas. 

When spreading fertilizer whether before planting a new lawn or overseeding bare spots in existing lawns, you should use a drop spreader or rotary spreader

Once you have a drop-type spreader or rotary spreader, and it’s ready to use, switch the dial to the right level, which is according to the amount of fertilizer that needs to be applied. 

Most spreaders don’t come calibrated right out of the box, so you’ll have to calibrate the settings if they aren’t right. 

Tip: When it comes to filling the rotary or drop-type spreader, do not do it over the grass, because any spillage is an excess application of fertilizer. 

Start spreading from the edges of your lawn first, and there’s no need to go slow or fast, just walking normally is fine. Make sure you don’t miss any areas and turn the spreader off at the end of each strip. 

4. Mowing your new lawn 

The good thing about planting new grass seeds is that frequent mowing is not required, but you will have to probably wait for up to 2 months before the first mow. 

In general, you should wait at least four weeks after your seeds germinate to run a mower on your newly planted turf. 

If you mow too soon, the blades and wheels of your reel mower, rotary mower, or power mower will pull the grass sprouts out of the soil surface. Another good way of determining mowing times is by keeping tabs on grass height, where grass that’s grown to 3 – 4 inches in height, which is when you can increase the frequency of mowing. 

However, it’s worth mentioning that the grass should be dry for at least 48 hours before first mowing because it can increase the chances of rut damage in a mowed turf.  

How to Prevent the Chance of Disease in New Lawns? 

It’s important to learn how to identify diseases in cool-season lawns and warm-season lawns because trying to control weeds and keeping your lawn healthy can be challenging if your lawn is plagued with an agent of diseases, grassy weeds, broadleaf weeds, and any type of noxious weed seed. 

There are several factors that can cause the risk of disease and weeds in your newly planted lawn, most notably susceptible lawn grasses, weather conditions, lack of adequate nutrients, and disease pathogens. 

Signs of the onset of lawn disease include: 

  • Circles of dead, sunken grass
  • Darkening, wilting, and dying grass blades can have an impact on turfgrass health 
  • Warm to hot weather conditions can cause brown patch lawn disease
  • Alkaline or acidic soil 
Brown Patch Lawn Disease

Final Thoughts

Applying lawn fertilizer to a newly planted lawn must be done properly and at the right time. The best way to spread fertilizer is with a rotary or drop-type spreader.

You should water the area where you plan on spreading grass seed a couple of days before application and make sure there are zero levels of pest infestation in the area or signs of poor soil. 

It is best to use organic lawn care practices and simple lawn solutions without the use of agricultural chemicals when creating a new lawn. Adding to this, stick to a regular maintenance schedule that includes watering and mowing for your new grass to thrive. 

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