How Much Grass Seed Do I Need?

Whether you’re reseeding an existing lawn or starting from scratch, there’s lots of advice on the process to follow. But when I was creating my lawn, my first question was, “How much grass seed do I need?”

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Getting the coverage right is one of the most important parts of the job. Too little, and you’ll be left with bare patches that fill with weeds before the grass has had a chance to spread. Too much can be just as bad. The seeds won’t have space to germinate, and roots packed too close together can rot.

So just how do you hit that sweet spot? That’s what we’re going to find out! Come with us on a journey to discover exactly how much grass seed you need to get your perfect lawn.

New lawn, reseeding or overseeding?

Some of the terminology around lawns can be surprisingly confusing. Everyone knows what a new lawn is – but what about the difference between reseeding and overseeding? You’ll need different quantities of grass seed for those different tasks, so it’s important to know what you’re doing.

Reseeding is what you do to cover up bare patches in your lawn. If moss, weeds or even your pet urinating on it has left spaces where there should be grass, you need to reseed.

The area will of course be a lot smaller than it would be for a new lawn, but the process is essentially the same. That’s because you’ll still be sowing new grass seed in a space where no grass exists at present.

Overseeding, on the other hand, involves sowing grass seed over an existing lawn. It’s a good way of encouraging thicker, healthier growth.

You’ll need more grass seed per square metre if you’re reseeding or starting from scratch than if you’re overseeding. Most commercial grass seed mixtures will state recommended densities for the two different processes on the packaging.

Choose the right grass seed

Choose the right grass seed
The Salutation Gardens

There are hundreds of different species of grass out there, and they have very different characteristics. That can even extend to needing to be sown at different densities. So start by choosing a grass that will suit your requirements.

If your lawn is shady, look for a grass mixture that will cope with lower levels of light. Bear in mind that even shady lawn mixes can struggle if the area is very dark. If trees or shrubs overhang the space, cutting them back or thinning them out can greatly improve your lawn’s health.

Next, think about how you’re going to use your lawn. Will children be playing on it? Are you going to use it as an outdoor entertainment space? If so, look for grass that can withstand higher levels of traffic.

Ryegrass is a good, robust variety, so look for mixtures with higher proportions of this. Dwarf ryegrasses are particularly good, as they won’t grow too long.

Ryegrass is, however, quite coarse. If you’re looking for a manicured green surface, a bowling green mixture may be more appropriate. These often use mixes of bentgrasses and fescues.

They will give you a smoother and more attractive surface. But note that they do require a lot of aftercare and are vulnerable to pests.

Working out your lawn size

Working out your lawn size
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Now you know what kind of grass seed you’re buying, you need to work out how much you’ll use. That means knowing the surface area of your lawn.

If your lawn is square or rectangular, this is very easy. Just measure the length and width, and multiply the two together to get the area. So a lawn 4 metres long and 3 metres wide will have an area of 3×4=12 square metres.

If your lawn is L-shaped, you can use the same approach. Just split it into two rectangles and add together the results of your calculations.

If your lawn is irregular, you’ll need to get out a piece of graph paper, or draw a grid with even squares. Measure your lawn at its widest, narrowest, longest and shortest places. Then sketch the shape of the lawn to scale on your grid. The easiest way to do this is to make one square one square metre.

Then add up all the squares that are fully covered by the lawn on your drawing. Next add in all squares where the lawn is at least half-filling the squares. The total will give you a decent approximation of the surface area.

Now add in at least 5 per cent extra for comfort. If you had lots of squares on your drawing that were just under half-full, increase that margin to 10 per cent.

You now have the surface area you’ll need to cover with your grass seed.

Seed density

Seed density
The Salutation Gardens

The next thing you need to know is how densely to sow your seed. In most cases, it will say this on the packaging. The measurement will usually be given in weight of seed per square metre of lawn.

Make sure that you’re reading the recommended density for your project! Remember, the quantities of seed you’ll need for a new lawn are quite different from those required for overseeding.

As a rule of thumb, new lawns will need between 25 and 30 grams of seed per square metre. But make sure you check the packaging of your chosen lawn mix. Some require denser planting of 35 grams per square metre.

You’ll need the same density as for new lawns if you’re just filling in bare patches. If that’s what you’re doing, you’ll usually want to look for the smallest available pack.

A good option can be to purchase a product specially designed for patches. These often contain a growing medium mixed with the seed. That means you won’t need to get hold of topsoil separately, nor to mix it with sharp sand. Miracle-Gro’s Patch Magic is a good example.

If you’re overseeding, you’ll need fewer seeds. Expect to use between 15 and 25 grams per square metre. As always, check the packaging to see what’s recommended for the variety you’re using.

If a range is given, consider how thin or thick your existing grass is. If it’s already well established, use less seed.

And in all cases, don’t be tempted to use more seed than is recommended. It won’t give you a better result. Seeds that are cramped may not germinate at all. And if they do, roots growing too close together can easily rot, especially in damp soil.

Purchasing the right amount of grass seed

Now you know both the seed density and the area of your lawn, you can calculate how much seed you need.

Make sure you’re using the same units for your measurements! If you’ve measured your lawn in square feet but use the quantities of seed for square metres, you’ll use far too much.

Multiply the grams per square metre for your project by the number of square metres of area you calculated earlier. Remember to include at least 5 per cent extra in that square metre total, to make sure you have enough seed.

That will give you your total seed requirement. For larger projects, you may need to divide that number by the weight of seed in each bag. That will tell you how many bags you need.

Sowing the right amount

Sowing the right amount
The Salutation Gardens

When it comes to sowing the grass seed, try to be as accurate as possible. Under or over-application can give disappointing results.

If you’ve got a seed spreader, it will make the job easy. You can set it to your required seed density. You’ll then just need to make sure you walk at the pace required by the spreader. Time yourself before you start using the spreader, so you get used to how fast that is.

If you haven’t got a spreader, take four one-metre-long garden canes, and tie them together into a square. This will mark out one square metre. Now measure the correct weight of seed for one square metre.

Place your cane square at one end of the lawn, and sprinkle the seed you’ve measured out inside it. Try to sow as evenly as possible. Holding your hand about 18 inches from the surface of the soil will give you good control.

Now move your square to the next patch of lawn and repeat the process. It’s fairly time consuming, but don’t be tempted to speed things up by guessing. If you end up with a patchy lawn, it will take you far longer to do it all again.

If you’re using a patch repair kit, remember that the densities will be quite different. That’s because the seed is already mixed in with a growing medium like coir. Follow the instructions on the packaging to get the best results.

You’re ready to buy your grass seed!

We hope you’ve enjoyed our guide to getting the right amount of grass seed for your project. Whether you’re repairing a few patches or laying a whole new lawn, the principles are the same.

Take your time to calculate your lawn’s surface area and to measure out the right amount of seed. Using a seed spreader makes the job quicker, especially for larger lawns. But don’t be tempted to take shortcuts by estimating quantities. You’ll only need to spend time later putting right mistakes.

Good luck with your next project. We’re sure your lawn will soon be looking great!

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