Skip to Content

Can You Fertilize and Overseed at the Same Time? (Answered)

If you are not happy with the state of your lawn, the grass is not evenly grown and most of them are becoming dry and lifeless day by day then it’s high time you think about overseeding.

So overseeding, is it just putting grass seeds on your lawn, what about the fertilizer, should you practice any precautions. Let’s have a deeper look at the topic.

Can you fertilize and overseed at the same time? 

It is highly recommended not to use fertilizer and overseeding at the same time. If fertilizing and overseeding are done simultaneously, the herbicide element present in fertilizer will stop the germination process. It is best to wait for 40-5o days after overseeding and then apply fertilizer.

Overseeding, adding grass seed to unturned soil. It is more likely to be done to introduce different types of grass and also get a fuller and thicker look out of your lawn. 

Now fertilization plays a significant role in helping the grass grow and get all the necessary nutrients to sustain good health.  However, fertilization also can cause massive drawbacks and abrupt overall growth if applied at the wrong time. 

Most of the fertilizer contains herbicide elements, if applied simultaneously while overseeding it will prevent the seed from germinating. So all your hard work and money would be wasted if overseeding and fertilization are done at the same time. 

There should be a minimum interval of 30 to 40 days between overseeding and fertilization.

Can you fertilize after overseeding? 

Yes, you can apply fertilizer after overseeding but you will have to wait until the seeds are fully germinated and all the necessary mechanisms are ready to receive the nutrients from the soil. A waiting period of 40 to 50 days or a month after overseeding is the suitable time for fertilization.

Before applying fertilizer, the waiting period is crucial for grass germination and survival. If you apply fertilizer at the same time while overseeding or not keeping the minimum interval of 40 days, the seeds won’t germinate due to the herbicide element found in fertilizer. 

The herbicide will treat the new grass seed as an unnecessary weed and eliminate them, so your newly planted grass seed will have no chance of survival in presence of newly applied fertilizer in the soil.

Jobe’s Organics 9026 Fertilizer, 4 lb

Can you fertilize before overseeding? 

Yes, you can apply fertilizer before overseeding but there should be a significant number of days between overseeding and fertilization. 

Let’s say you have applied fertilizer 1 or 2 weeks before overseeding, now the old grass will get all the necessary nutrients to grow and it will be difficult for the newly planted grass seed to germinate and survive in the shadows of old grass. 

It’s not only that there is one more issue, the herbicide present in the fertilizer might stay in the soil for 15 to 20days, so newly planted seeds won’t germinate in such an environment. So the best thing to do is apply fertilizer 20 to 30 days before overseeding. 

As you are gonna keep the soil unturned and trying to get a fuller look out of your lawn, you need to keep an eye on the major factors like fertilization. Overseeding and fertilization at the same time should be completely avoided along with fertilizing just a week before overseeding. 

Can I overseed and fertilize at the same time in the fall or spring? 

No, you shouldn’t fertilize and overseed at the same time in fall or spring. If you are thinking about overseeding then Spring is the most suitable time to do it. However, the simultaneous overseeding and fertilization will bring you nothing but disappointment. 

You were looking for a fuller look out of your lawn but putting fertilizer and overseeding at the same time means all your hard work is sure to go in vain. 

Most fertilizer has herbicide element, it’s known for getting rid of unnecessary weeds but if you apply fertilizer while overseeding it will eliminate any chance of germination and your lawn won’t be growing any new grass. 

What do you put down first, grass seed or fertilizer? 

Between grass seed and fertilizer, It’s better to put the grass seed first. Putting grass seed first and waiting for it to germinate increases the chances of survival of grass. 

If fertilizer is applied first then the herbicide will prevent the newly planted grass seed from germinating and also old grass would go bigger so you will have to go through more hurdles to achieve your goal. 

Putting fertilizer first can also be practiced but you will have to wait for 30 days to get rid of the herbicide concentration from the soil and then put grass seed.

Osmocote Smart-Release Plant Food Plus Outdoor & Indoor, 8 lbs

How soon can you seed after fertilizing?

After fertilizing you should at least maintain the waiting period of 20 to 30 days. The herbicide present in fertilizer will wear out in the meantime but if you don’t maintain a significant interval between the fertilization and overseeding then two things can happen. 

First of all, newly planted seeds won’t germinate, the second thing is your old unevenly grown grass would show growth and you will have to work on your lawn to make it suitable for new seeds, it’s gonna add up your chores quite a bit.

How to overseed and fertilize lawn in fall & spring?

The following steps will help You to overseed and fertilize lawn in fall & spring –  

Cut the old grass:

Mowing the lawn or cutting the existing grass to a shorter length is gonna help a lot while overseeding. You can get rid of lifeless & dry grass as well as get an overall idea about the places where you need to put extra attention.

Identify and solve the existing problem:

you are obviously thinking about overseeding because you are not happy with the present state of your lawn. 

There could be lots of things wrong with your lawn, poor soil quality, bad drainage system, insufficient nutrients concentration, irrigation scarcity, lack of sunlight, unsuitable grass variety, and much more. 

You need to identify and solve the problem otherwise overseeding won’t give you the desired result you are looking for.

Maintain the waiting period

the waiting period between applying fertilizer and overseeding holds quite significant value. The herbicide present in fertilizer won’t let the new seeds germinate if overseeding and fertilizing are done at the same time. 

You need to wait at least 15 to 20 days after fertilizing or you can overseed and wait for 30 to 40 days to fertilize.

How often to fertilize after overseeding? 

Too much of anything is bad, plants need fertilizer to grow and receive the essential nutrients to survive but if you overdo it there are sure to be consequences. So you need to know about the safety limit for applying fertilizer. 

Applying fertilizer once a month is enough for your lawn. If you are thinking of applying fertilizer every week or in intervals of every two weeks then the increased volume of nitrogen and other salts can be lethal for your lawn to grow grass or anything else.

How long to wait to fertilize after overseeding? 

The waiting period for fertilization you need to maintain after overseeding is 40 to 50 days. Generally, grass seed needs two to three weeks to germinate and even longer to be fully prepared to receive the salts and other minerals. 

If you don’t wait and apply fertilizer within one week, the grass seed might not germinate and all your efforts will go in vain. Although there is special starter fertilizer available for newly planted seeds, you would have to wait a week or two before applying it.

Do you have to aerate before overseeding? 

Aerating the soil before overseeding will help the seeds to penetrate easily through the soil. If you are applying fertilizer before overseeding then make sure you aerate the soil. It will open up little pores which will benefit both the soil and the seeds. 

Miracle-Gro Shake 'N Feed Tomato, Fruit & Vegetable Plant Food, Plant Fertilizer, 4.5 lbs.

What fertilizer to use with overseeding? 

Natural compost can be the best fertilizer for your lawn. However, it tends to wear out fast, you can aerate the soil to make it last longer. You can also apply lawn starter fertilizer which is specifically designed to be gentle on the soil and grass.

Does overseeding hurts weeds? 

Actually, it’s not the overseeding but the steps before overseeding like applying fertilizer with herbicide and mowing the lawn that gets rid of the weeds. Only applying grass seed on the lawn won’t hurt the weeds

Final Thoughts:

As a rule of thumb, fertilization and overseeding should not be done at the same time. Seeds will not germinate if fertilization and overseeding are done at the same time.  One should wait at least 6-7 weeks after overseeding before applying fertilizer or apply it one month before overseeding.