When is the Best (and Worst) Time to Plant Grass Seed in the UK?

by Daniel Hunter

When to sow grass seed? That is the question!

The answer is the same whether you’re sowing a new lawn from scratch or overseeding an existing one.

Sow your seed at the right time and it’ll germinate and grow well. Do it at the wrong time and even the best lawn seed money can buy won’t germinate.

But don’t worry, uncle Daniel is here with all you need to know.

The Best Time to Sow Grass Seed in the UK

To get the best results you need to sow grass seed when;

  • It’s warm, but not too warm – grass seed needs soil temperatures of at least 8° Celcius to germinate. Some species need it to be warmer still. That said, it shouldn’t be too hot, otherwise, the seed will bake.
  • There’s plenty of moisture – provided by rain is ideal but supplemented by a sprinkler if needed.
  • There’s lots of sunlight – to aid photosynthesis and growth.

And which seasons provide these conditions?

Spring and Autumn.

Early Autumn is the Best Time to Sow Grass Seed

autumn leaf on lawn

This is for a few reasons;

1. The Soil is Nice and Warm

Grass seed needs soil temperatures to be at least 8° Celcius to germinate well. In early autumn the soil is still warm from the summers sun. This makes a cosy warm seedbed.

2. The Rain Helps Germination

If the weather is on your side, the rain will help soak the ground and provide vital moisture to the warm soil. Grass seed can’t germinate without it!

3. There’s Plenty of Sunlight

For grass seed to germinate and grow, it needs plenty of sunlight and early autumn provides it. Better yet, the air temperature is cool enough to not bake the seed or new seedlings.

4. It’s Not too Hot

As the seasons change from summer into early autumn, the temperature often drops. It’s warm but not so hot that it dries out the soil or bakes the seed.

5. There Are Far Fewer Weed Seeds Around

At the end of the growing season, there is far fewer weed seed floating around. That means there’s less risk of them germinating in bare soil.

6. There Aren’t As Many Birds

Don’t get me wrong, I love having birds in the garden. But when they eat my grass seed? That’s when we have a problem! During the autumn, lots of birds migrate for the winter and that means there aren’t as many to scoff my seed.

7. Grass Growth Habit Changes

This is one of the best reasons for sowing grass seed in Autumn. As the weather cools down, you’ll notice that leaf growth slows. This happens as the grass draws nutrients from the leaf into the roots. Priority changes from leaf growth to strong root development.

The benefit is that when spring arrives, your lawn will have strong roots to support leaf growth. As a result, your lawn will look much nicer, much earlier in the season.

Spring Is Also a Good Time For Planting Grass Seed

spring grass

Spring is also a good time to plant grass seed for many of the same reasons autumn is. For example, there’s plenty of sulight and rain.

But there are some disadvantages…

First, germination often takes longer in spring than it would in autumn. This is because soil temperatures are quite cold coming out of the winter. The soil needs time to warm up.

Rye grasses can germinate in cooler temperatures of around 8° celcius. Fescues and/or bent grasses need warmer conditions so expect them to take even longer.

Second, when spring arrives, grass changes its focus from root development to leaf growth. You’ll need to make sure there are plenty of nutrients in the soil to support this growth. If you’re sowing a new lawn, use a pre-seeding fertiliser when you prepare the ground. If you’re overseeding an existing lawn, use a spring lawn feed.

Third, plants set their seeds in spring and that means weeds do too. Your weed control game needs to be sharp if you want to prevent your lawn falling victim.

And fourth, the frickin’ birds are back! And nothing tastes as good as grass seed after winter migration. You’ll need to do what you can to prevent birds from eating your grass seed.

When NOT to Lay Grass Seed

So autumn and spring are good both good times of the year to sow grass seed.

So that leaves summer and winter.

Summer Isn’t Great

The summer is too hot and dry.

If you spread grass seed during the summer months, chances are you’ll bake the seed and kill it.

You’ll not be able to keep the ground moist enough either. You could water three times a day but you’ll lose most of it to evaporation.

Don’t Do it in Winter Either

don't sow grass seed in winter

Believe it or not, there are some that say winter is a brilliant time of year to sow lawn seed. They call it ‘Dormant Seeding’.

The idea is that as the soil warms up entering spring, the grass seed will start to germinate. In theory, your lawn will have grown earlier than it would have otherwise.

But here’s sowing grass seed in winter is a dumb idea…

Our climate and weather patterns are too unpredictable. We often get a mild winter and sure enough, the grass seed germinates. And for a while, it looks like ‘Dormant Seeding’ worked.

Until we get a hard frost.

After which the grass turns yellow and dies. This happens because the grass’ new roots aren’t strong enough to cope with that kind of stress.

So don’t lay grass seed in winter. Wait until the spring when the risk of frost has gone.

Even better, wait until autumn.

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