Will Grass Seed Germinate on Top of the Soil

By Brian Mounts | Feb 15, 2020
Will Grass Seed Germinate On Top Of Soil

Spreading grass seed onto your lawn isn’t as straightforward as it might seem. Have you ever spent a couple hours one spring day sowing grass seed, only to realize a month or two later that almost none of your hard-earned seeds had actually germinated? Maybe you were left with a sad, patchy facsimile of the lawn you had dreamed about, or maybe it grew but not quite in the way you had intended.

Or maybe you’re a first time homeowner, and you’re not sure what the best way to plant grass seed is. In any case, this article will help.

The short answer is: yes, grass seed will germinate on top of soil, but you may need to do a little extra work for good results — just leaving it sitting on top of the soil probably won’t get you the kind of lawn you want.

How Does Grass Seed Germination Work?

Besides the soil, which we’ll get to in a minute, there are four main components which are crucial to the germination of grass seed:

  • moisture,
  • light,
  • oxygen, and
  • temperature.

Grass seed needs all three to properly grow; without even one of these components, it simply won’t germinate.

If you go to the store and pick up a bag of grass seed, there’s something you should notice about the seeds themselves: they’re all quite dry. Before you actually plant and water them, grass seeds contain very little moisture.

That’s why watering them is so crucial.

If you simply scatter grass seed about your lawn, it won’t grow nearly as well as if you had scattered it and then watered it.

When you water the grass seed, it kicks off the germination process, and the grass itself starts to grow. After that, however, moisture remains an important condition for your grass to grow tall and strong. Without damp soil, you’ll likely have stunted, rather tufty looking grass as opposed to a full, lush lawn.

The second factor important to grass seed germination is light.

Once the seeds start germinating and grass begins to shoot up, it’ll need light to grow properly. Like pretty much all plants, grass contains chlorophyll. It metabolizes food using sunlight as energy. Without a decent supply of sun, grass simply won’t grow or it won’t grow as quickly.

Third, grass needs oxygen to grow properly.

At first, the only ingredient a seed really needs to begin the germination process is water. But a short while after you water grass seed for the first time, it starts needing oxygen to continue sustaining itself and its rapid growth.

This is why it’s not good to over-water your lawn; the soaked soil will be too heavy and it’ll prevent the grass seed from accessing a necessary amount of oxygen. If the soils stays wet for a long period of time, the grass may even just die.

It’s also not a good idea to cover your grass seed in several inches of soil, for this very reason.

You want a light covering of soil so that your seeds are at the correct temperature and can access the nutrients they need, but you don’t want to bury them so deeply that they’re deprived of oxygen.

Finally, the last ingredient that’s important to seed germination is temperature.

Grass seed is generally rather sensitive to temperature, so choosing the right time of year to plant it is important. Also, remember that the soil in your area is probably a few degrees cooler than the air itself.

That said, different breeds of grass have different planting periods. Cool-season grasses are best to plant during the early spring or fall, while you’ll want to save warm-season grasses for late spring and early summer. Some breeds may even need fairly specific temperature ranges, so make sure you look at the label carefully when you buy a bag of new seed. Also, temperature is another reason why covering your grass with a slight bit of soil or straw is important; it’ll keep the grass warm enough to properly germinate.

Will Grass Seed Germinate On Top Of Soil?

Simply put, yes, grass seed will germinate if left on top of soil. The seeds will need sunlight, oxygen, moisture and the correct temperature to grow, as long as there’s also soil that it can absorb the appropriate nutrients and moisture from. However, this is hardly an ideal state for grass seeds.

If they’re just laying on top of the soil the temperatures they’re exposed to won’t be very consistent and they can be easily picked off by birds. Furthermore, it’s harder for seeds to absorb moisture and nutrients like nitrogen if they only have some surface area in contact with the soil, as opposed to being fully surrounded by it.

That’s why covering your seeds with a thin top layer of soil (through raking) and or covering it with hay are both attractive options in comparison.

Should I Cover My Grass Seed With Hay?

You may have heard that you need to cover your grass seed with hay or straw for it to germinate properly. While this isn’t strictly necessary, it can help your grass grow, so if the option is available then you can go ahead (though paying attention to moisture and covering your grass with soil is probably more important).

Straw or hay serve a couple of functions when you lay them down over freshly-sown grass.

  1. First, they protect the seeds from birds and other animals who would otherwise be able to simply pick the grass seeds up off the ground.
  2. Secondly, they keep the grass warm, ensuring that it’s at the correct temperature to germinate.

These issues can also be solved by simply raking your grass seeds into the soil (which you should probably be doing anyways), but adding an extra layer of hay certainly won’t hurt.

See my full grass growing guide here for more helpful tips – no opt-in needed.

Do You Have to Rake In Grass Seed For It To Germinate?

The answer here isn’t quite black and white: if you don’t rake your grass seed into the soil, it’ll still grow a little bit, and depending on your climate, area and breed of grass, it may even grow decently.

However, raking grass seed is usually the best choice, because the seeds need the soil to absorb the moisture and the nutrients necessary to grow. Simply leaving them lying on top of the soil is a bad choice for a couple of reasons.

  1. First, they won’t be as moisturized or well-fed as they otherwise would be if they had been surrounded by soil.
  2. Second, if they’re simply lying on top of the soil, then it’s relatively easy for birds and other predators to eat them.
  3. Finally, if they’re lying on top of the soil their temperature won’t be consistent, and it won’t be as warm as it would be were they surrounded on all sides.

Because of these reasons, lightly raking your grass seed when you plant it so that it’s covered in a thin coating of soil is a good idea.

That said, don’t get too enthusiastic about covering your grass seed with soil! If you cover the seeds more than a fraction of an inch (think ¼ or ½), it’ll be hard for your grass to get the oxygen and light to grow. Simply raking the seed so that it is lightly covered should be enough.

How Much Should I Water Grass Seed If It’s On Top Of Soil?

Be careful! This is one area where more does not always necessarily mean better.

Grass needs a good, consistent supply of moisture to grow, so the soil you plant your grass seeds in should always be wet. However, overwatering your grass seeds will actually kill them, because grass needs both moisture and oxygen.

If you overwater your seeds, the soil goes from being damp and moist to being heavy and wet. In such a scenario, the seeds can’t get the oxygen they need not only to survive, but to grow.

Right after you seed, you can water your lawn lightly a few times a day, but don’t go overboard on it. The goal is to keep the soil surrounding the seeds damp, but not soaked. While watering, you should stop before you notice puddles starting to form on the surface of the soil.

If you’re not sure about whether or not you’ve watered your seeds enough, the answer is simple. Just walk over and check the soil! If it feels dusty and crumbles apart in your hands, then it could probably use a little more water. But if it’s dark colored and has a moist texture, then you can stop.

Conclusion

So, to put it in basic terms: yes, grass seed will indeed germinate when it’s left on top of soil. However, these aren’t ideal conditions, and they likely won’t lead to a lush, healthy looking yard.

If you truly care about curating a picturesque front yard, then it’s actually best to cover your grass seed with soil through raking it into the ground, and possibly with a little bit of hay or straw on top.

Doing so will protect your grass seed from the elements and from predators, while keeping it warm and moist enough for the seeds to germinate without suffocating them. Just remember not to over-water your seeds or cover them with too much soil. Doing so will hurt your grass seed just as much as leaving it bare on top of soil will.

As long as you keep these things in mind, and you take good care of your grass as it’s growing, you should be on your way to a magazine cover-worthy lawn soon enough. Happy planting!