When to Fertilize New Grass for Best Results?

When to Fertilize New Grass for Best Results

Grass typically doesn’t need a lot of work to grow, but the same can’t be said for growing a new lawn. If you’re growing new grass, you’ll need to put in enough effort so that the seeds can germinate easily. Ideally, your grass roots should reach deep into the ground so that your lawn is thick, green, and resilient. 

Fertilizer is an effective way to provide new grass with important nutrients. However, it’s important to use fertilizer at the right time in the grass growth cycle. Fertilizers also come in several types which have different levels of nutrients within. It’s important to choose the right one, as saturating your lawn with nutrients can burn your grass. 

If you want to know how to use fertilizer on your new lawn, you’re in the right place! You’ll find out what the best time to use fertilizer on new grass is in this article. We’ll also explain why it’s important to fertilize new grass in the first place, as well as some different types of fertilizers that are available to purchase. 

Why Is It Important to Fertilize New Grass?

Fertilizers are packed with potassium, nitrogen, and phosphorus. These are important nutrients that can make your soil healthier. Unhealthy soil doesn’t have enough of these nutrients, so it won’t stand up well to fungus, erosion, weeds, and pests. It’s also easier to grow grass on healthy soil. 

However, an excess of fertilizer or using the wrong type can have negative effects on your soil. If the earth is overflowing with fertilizer, the nutrients can pass through to the water table and cause runoff. When fertilizer chemicals runoff, they can start forming toxic algae in lakes and nearby ponds.

This can be harmful to anyone who comes in contact with the water. This is why fertilizers are heavily regulated, as you can only buy a specific amount at any one time. 

Types Of Fertilizer

You’ll need to choose the right fertilizer for your grass. Fertilizer comes in two types: regular slow-release fertilizer, or starter quick-release fertilizer. 

Weed and Feed fertilizers use herbicides to stop weeds from growing. Don’t use these if you’re planting new grass seed, as they will stop your grass seed from growing too. 

If you have certain types of weeds growing in your location, you may be able to find fertilizers that specialize in preventing them from germinating. For example, several brands stock products that block dandelions or crabgrass, allowing new grass to grow as a result. 

Fertilizers also come in different compositions. These are organic, chemical, urea, and ammonium sulfate. 

Organic fertilizers are made of natural minerals. These can be plant, animal, manure, blood meal, and fish by-products. These tend to be slow-release fertilizers, which are often needed in the fall.

Chemical fertilizers are made from animal, petroleum, or rock-derived substances. These are often refined so that the nutrients are heavily concentrated. This increases the absorption rate, which is good for use in spring. 

Urea fertilizers are rich in nitrogen and quick-release products. As urea is a byproduct of ammonia, it’s normally less expensive to purchase. Despite this, they have to be mixed in with soil so that important gases aren’t lost as they convert into nitrogen. Grasses that thrive in acidic soil do well with urea fertilizers. 

Ammonium Sulfate fertilizers are only used on heavily alkaline soil. Ammonium sulfate adds sulfur, which lowers the soil’s pH level. As you apply the fertilizer, the ammonium sulfate chemicals can be accessed immediately by the roots. If you use these, always dilute in water beforehand.

What Does Poor Soil Mean?

Poor soil can harbor weeds, insects, and fungus. These can cause disease, soil erosion, and patchy grass on your lawn. This isn’t just harmful to your grass, but it’s also bad for any plants growing in the surrounding area. 

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Three Important Nutrients

As stated previously, lawn fertilizer contains three main ingredients, though different products will have different ratios of each one. Nitrogen helps new grass to grow a lush green color, phosphorus helps support the new roots, and potassium helps prevent the disease from affecting the new grass. 

The ratios will look like three individual numbers with dashes in between them. These are called NPK ratios, as they display how much nitrogen (N), phosphorus (P), and potassium (K) are in each fertilizer. The numbers will be in the order below:

Nitrogen – Phosphorus – Potassium 

If you want to know what fertilizer is best for your lawn, you’ll need to buy and perform a soil test. Make sure that your kit measures pH levels and assesses the three nutrient levels within your soil. Grass thrives in soil with a pH level between 6.5 and 7.

This is slightly acidic. If the soil is too acidic or alkaline, your seedlings will struggle to take in any nutrients, even if your soil is rich and abundant. Soil that’s too acidic can also affect the soil, which can lead to fungus and a loss of beneficial bacteria. 

If your soil test shows that your soil is too acidic, you can try adding lime. Lime will help to neutralize the soil and increase the pH level. The most common lime found in stores is dolomitic lime, as it’s made up of magnesium.

Before you apply the lime, aerate the soil. This involves making little holes in the soil, so the grass roots can absorb air, water, and nutrients better. Aerating will also help the lime pass deeper into the soil. 

New grass needs a starter fertilizer. These will have greater amounts of phosphorus and nitrogen that are released into the soil at a faster rate.

The seeds will absorb the nutrients quickly and efficiently. Quick-release nitrogen also has an advantage, as it allows the seeds to take up more potassium. Some locations are known for restricting phosphorus usage to people who are growing new lawns. 

Aerating Compacted Soil

Before you go in with fertilizer, you may want to prepare your soil beforehand. Aerating is just one way of doing this. It effectively airs out the soil so that it can breathe better. 

To do this, you’ll need to take small plugs out of your lawn. These holes will let oxygen through to the roots within the soil. When you finish aerating, use a brush to move sand into the holes. This improves drainage and makes a seedbed in which you can put new seeds. 

If your soil is compacted to over 2.5 inches, use a rake to work it so that it loosens slightly. Modify the remaining soil, then apply new grass seed or new sod. 

After you look after your lawn for a few years, you may find earthworms within. This isn’t a bad thing. Earthworms aerate your soil naturally, which reduces the need for you to do it yourself. 

Once your seeds germinate and start showing, cease using starter fertilizer. These seedlings aren’t baby ones anymore. They’ve grown older, so they need regular fertilizer as food. 

The Right Ratio For Existing Lawns

Existing lawns do well with fertilizers containing a lot of nitrogen, but they don’t require that much phosphorus or potassium. Your fertilizer should have an NPK ratio with a greater first number, and smaller second and third numbers.

This may look like 30-0-0 or 27-3-3. Fertilizers with these ratios are best for maintaining the green color on existing lawns. 

The Right Ratio For New Lawns

New grass seed does well with starter fertilizers that have an NPK ratio near 21-22-4. Nitrogen, phosphorus, and potassium should be quick-release nutrients. This ensures that your new seeds will absorb these nutrients immediately after application so that your lawn starts growing at a faster rate. 

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Keep in mind that soil generally contains potash, which is a source of potassium. This is why a lot of fertilizers don’t contain high levels of potassium. 

When Is The Right Time To Fertilize New Grass?

Before you start planting your grass seed, you should ensure that your soil contains the right nutrients. 

Once you’ve prepared your soil for the grass seed, you need to fertilize your soil with a starter fertilizer before planting. You can do this at the same time or before you disperse the seeds. 

Make sure that you don’t reapply the starter fertilizer once you’ve applied it. If there is an excess of nutrients, they can damage and burn the existing grass. After you’ve planted your new grass, it’s best to wait 6-8 weeks, then use a classic organic fertilizer with greater nitrogen content. 

6-8 weeks may seem like a long time, but fertilizing too soon can be bad for your lawn. You may want to fertilize soon after you plant your grass, but this can run off into the water table and burn your grass. At a minimum, wait four to six weeks before going in again with fertilizer, but 6-8 weeks is the recommended amount of waiting time. 

Beginning of Spring

Seeds start germinating during this time, in February, March, and April. 

End of Spring

Weeds usually start forming in late spring, in April, May, and June. The weeds may be young here, but they are very efficient and lively.


It’s best to maintain your lawn during the hotter months. The Sun is an amazing food source for grass and plants. The summer months, June, July, and August provide enough sunlight for your lawn so that it gains important nutrients. This helps them grow and maintain rich green grass.

End of Summer

Winter conditions start appearing as summer finishes. August, September, and October are when new grass growth starts slowing down. Weeds also begin preparing for growth in this period. 

Method For Seeding New Lawns

1.Dethatch and aerate your lawn if it needs it. 

2. If your lawn doesn’t need to be dethatched, go over the earth with an iron rake to remove dead grass and loosen the soil. 

3, Make sure that the area you want to seed is free from dead grass. 

4. Take your starter fertilizer, then apply an even layer over the area. 

5. Lay a large amount of grass seed down. Make sure that the seeds are right for your planting area and growing conditions. 

6. Work the seed into the loose soil. The underside of a leaf rake works well for this. 

7. Put ¼ to ½ of an inch of compost over the grass seed. This gives nutrients to the new seeds and also helps to keep the soil moist. 

8. Regularly water the compost and seedlings, keeping them moist until they have started sprouting. 

9. Once the seedlings have started showing, water deeper into the soil, but less regularly. This will encourage root growth.

10. Keep monitoring the grass seedlings. Once they have reached 3 inches in height, use a sharp mower blade to mow the grass. You’ll only need to take off ½ to ¾ of an inch off. Put these clippings into a bag and remove them. 

11. When the grass grows 3 inches tall again, mow in the same way. Don’t take off more than one inch. 

12. When 6-8 weeks have passed since seeding, you may apply organic nitrogen-rich fertilizer. 


Fertilizers may be full of important nutrients, but they can also be packed with chemicals. Composting is another fertilizing method that doesn’t use any chemicals. Application is simple enough, you just apply a thin layer on your lawn every two years. 

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You can go longer between applications, but if you want to do so every 3 to 4 years, ensure that your compost is rich and dark. This encourages your soil to absorb these nutrients so that it becomes rich and abundant. Compost is a natural way of increasing your soil’s nutrient content. 

You can make compost at home by collecting decomposing materials, but you can also find it at composting centers in your area. These centers are places where nearby residents can hand in grass and leaf clippings.

If you can’t find one of these, try contacting your nearest plant nursery. If you have too much compost on your hands or have a smaller lawn, you can share your supply with neighbors and friends. 

Do You Need To Fertilize Again in Fall? 

You can support your grass before winter by using fertilizer in the fall. This product should have a decent amount of slow-release nitrogen and should be applied before the first frost occurs.

This is normally around November 1st for southern locations, but a lot earlier than this for northern states. 

Using nitrogen fertilizer before snowfalls can cause snow mold, which can kill the grass on your lawn. 

If you have an existing lawn, it’s best to fertilize it when spring comes around. The grass will look green again and you should have mowed the lawn a few times. Use your fertilizer six weeks after overseeding, making sure that your fertilizer has a high nitrogen content. 

If you haven’t been looking after your lawn, you can try using a slow-release fertilizer at the end of spring or early summer. Leave 45-60 days in between each application. 

Fertilizing New Grass Seed

Make sure that your selected planting area is free of weeds. After weeding the area, use a rake to gently loosen the top layer of soil. 

You can then fertilize the seeds. Apply it to the soil, or apply it simultaneously while you lay the grass seed down. If you have a larger area, a broadcast spreader can help you spread the grass seed. 

You’ll need to cover the seeds with a thin soil layer. Do this by using the same broadcast spreader to apply soil, or using a rake to move the soil in one direction. If you water your seed, do so lightly. Larger streams of water can move the seeds out from the soil. 

The Bottom Line

Lawn starter fertilizers are great for fertilizing new grass, as they are rich in phosphorus and contain quick-releasing nitrogen. 

Slow-release ones, known as regular fertilizers, are rich in nitrogen. These are better for planting sod or giving established lawns a new lease of life. If you want to apply a starter fertilizer, do this while right before planting the grass seed or as you do it.

Use a slow-release fertilizer again after six weeks, but no earlier than four. Using fertilizer too often can damage your lawn and in more serious cases, can be harmful to the environment. 

You can give your grass a helping hand in winter by applying fertilizer before the first frost. Use a phosphorus-rich fertilizer in the fall to motivate roots to grow deep in the soil. Come spring, your lawn will be prepared for organic nitrogen fertilizer, so that it reaches a bright green shade. 

This may seem like a lot of information, but in reality, grass only needs a little bit of maintenance to grow well. As long as you use the right fertilizers at the right time, your lawn should grow thick, green, and luscious. Just a small amount of care can make your lawn the envy of the whole neighborhood!