When to Sow Grass Seed (And When NOT to) For Best Results

Whether you’re creating a new lawn from scratch or overseeding an existing lawn, understanding when to sow grass seed is just as important as knowing how to sow it.

Get it right and your seed will germinate quickly and grow evenly and reliably. However, get it wrong and even the best quality lawn seed money can buy might not germinate at all.

This article will explain when is the best time to sow grass seed and why.

I’ll also tell you when you shouldn’t do it.


The Best Time to Sow Grass Seed

Ideally, you should sow lawn seed when growing conditions are ideal.

This means;

  • Warmth – when temperatures are consistently above 8-10 degrees Celcius but not high enough to bake the seed
  • Plenty of moisture – usually provided by rain but supplemented by a sprinkler if needed
  • Lots of sunlight – to encourage growth and photosynthesis

Autumn and spring are the two seasons that provide the best growing conditions although autumn is ideal.

Autumn: The Ideal Time to Plant Grass Seed

when to plant grass seed uk

There are a number of reasons why autumn is the ideal time to sow grass seed.

The Soil is Warm

Firstly, in order for the seed to germinate as quickly as possible, it needs warmth. When September rolls around, the sun will have warmed the soil over the course of the summer months. This warm soil makes the perfect seedbed.

The Rains Return

The second ingredient grass seed needs to germinate and grow is water. Autumn generally brings rain which dampens the warm soil.

There’s Still Plenty of Sun

And thirdly, new grass needs plenty of sunlight to photosynthesise and grow. Autumn generally provides plenty of sunlight at temperatures that won’t bake the seed or stress the newly growing seedlings.

Fewer Weeds

Weeds are a lot less prevalent in autumn too. The chances of them invading any bare patches of soil are much less.

Fewer Birds

Also, there are fewer birds to snack on the seeds as many species start to migrate for the winter.

Growth Habit Changes

At the end of the year, the growth habit of grass changes. As the temperatures start to decrease, leaf growth slows and the grass places more priority on root development in preparation for the harshness of winter. This means you have really strong, resilient grass.

And the best bit?
Once winter has passed, you’ll have a beautiful, well established lawns to enjoy in the spring.

Spring: Another Great Season

best time to seed grass

While it’s not as perfect as autumn, spring is another great time of year for sowing grass seed.

The sun gets higher in the sky and the temperature starts to rise while the rains provide the moisture needed for germinated.

However, the cold weather will have cooled the ground over the winter so germination generally takes a little longer, especially in areas of shade.

Grass places more emphasis on leaf growth during the spring. This means that once germination happens, growth is fairly quick, giving you a nice green lawn surface fairly quickly.

You’ll need to keep a keen eye out for weeds popping up as they’re rife during the spring. If you’re sowing a new lawn or overseeding after treatment like scarification, weeds can settle and germinate in areas of bare soil.

Using a weed killer on new grass could also kill it so you’ll have to pull them by hand.


When NOT to Plant New Grass Seed

It’s just as important to understand when NOT to plant lawn seed so you don’t find yourself wasting both time and money.

Don’t Sow in Summer

Because lawn seed needs temperatures in excess of 8-10 degrees Celcius, many gardeners make the mistake of sowing seed during the summer only to see that it doesn’t germinate.

This is because it’s too hot and dry and the sun is like to bake and kill the seed.

In order to provide enough moisture to keep the soil moist, you’d be watering all day. Even then, you’d lose so much moisture to evaporation.

Avoid Winter Too

There are a few people who advocate sowing seed during the winter. This is known as Dormant Seeding.

The idea behind it is that it saves time in the spring.

However, the problem with this way of sowing lawn seed is that the weather is so unpredictable. We rarely get significant snow and we often get mild conditions followed by frosty cold snaps.

Milder conditions can encourage germination but the following frost could kill the seedlings.

So it’s often a waste of both time and money.


In Conclusion

Knowing when to plant grass seed is just as important as knowing how to sow it.

So to re-cap;

  • Autumn (generally September) is ideal
  • If you can’t wait until September, do it in the spring (April/May is generally best) but keep an eye out for weeds

However, all this advice is predicated on the weather.

The best time to plant grass seed is when the weather is doing what you want it to. So if we get an Indian summer and it’s too hot in September, wait until October, or make sure you water lightly every morning and evening to keep the seed moist.

Timing is everything and unfortunately, the UK weather isn’t always easy to predict so it’s always best to consult a 14-day weather forecast and try to choose the most ideal window.

That said, your new lawn will be worth the time and patience.

About Tim Stephens

I'm a professional gardener with degrees in Horticulture & Landscape Gardening. I want to help you create the garden of your dreams. I want your garden to look like it’s maintained by a professional. As if I was there doing it all for you!

1 thought on “When to Sow Grass Seed (And When NOT to) For Best Results”

  1. Thank you for the article. Fall was not good this year for me to overseed my lawn and fix bare patches as weather did not cooperate, but should have done if had known all of this snow was coming to Nebraska. I have always preferred fall over spring, mainly because of weeds. Most of our snow could melt this week (March 1). Is it too late to overseed at that time thinking about the weeds to come and using weed and feed? I think that I have read that you should mow a time or two. Thanks,Shirley


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