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How to Plant Grass Seed on an Existing Lawn?

If your lawn is looking a little tired or drought-damaged, you might want to sow some new grass seed into it. This guide will show you how to plant grass seed on your existing lawn in 8 simple steps. In this article, I’ll also cover the best times to grow grass seed, how often to water, and what to do if your grass seed just won’t grow.

Get your lawn looking green and lush again with my straightforward advice.

When Is It Best to Plant Grass Seed on an Existing Lawn?

Planting grass seed on an existing lawn – known as ‘overseeding’ – can be done at any time between March and October. There are a couple of crucial factors to bear in mind though: the moisture levels and the soil temperature. These are the two most important things to think about before you sow the seed.

Firstly, moisture levels. You will need regular rainfall or watering to encourage seed germination. Giving your grass seed enough moisture is very important until the new seedlings are at least 5cm (2 inches) high.

Secondly, the soil temperature needs to be at least 8֯C – equivalent to an air temperature of about 10֯C.

The Best Month to Plant Grass Seed

September is generally seen as the best month to sow new grass seed. The soil is still warm from the summer, and there will be more rainfall. Weeds are dying off, which means less competition from them in your lawn while you are trying to establish new grass.

In September it is still warm enough for your grass seedlings to get established and for their roots to develop. By the following spring, the grass will be strong and ready to withstand dry spells much better.

Watering Lawns in Times of Drought

If your area is experiencing a drought and there are hosepipe bans in place, you will not be able to water new grass seed you’ve sown. Think about postponing the work until you know you will be able to water the lawn adequately.

Ideally, you will have plenty of regular rainfall to give your new grass seed all the moisture it needs. A little light watering every now and again probably won’t be enough to get your new grass growing, so drought conditions are the worst time to sow seed.

How Do You Choose the Right Grass Seed for Your Lawn?

You can buy various different types of grass seed mixtures. Which one you choose will depend on how you use your lawn, and what the conditions are like in your garden.

Is your lawn in the shade or full sun? Do you need the grass to be hardwearing for a family and pets, or are you looking for something more ornamental and lush? What sort of soil do you have, and which grass suits it best?

There are lots of different options, so it’s worth having a good look around before you buy.

How to Sow an Existing Lawn with Grass Seed – Easy 8-step Guide

The ideal time to sow seed is straight after a good deluge of rainfall, as there will be plenty of moisture in the soil to kick start the growth of your seeds.

What you’ll need:

  • Lawnmower
  • Grass seed mix
  • Multi-purpose compost
  • Sand
  • Bucket

Spade or trowel

  1. Prepare your lawn by mowing it short – this will help to stop your existing grass competing with your new seedlings so much. Collect and remove cut grass.
  2. If you have problems with moss in autumn and winter – causing a ‘spongy’ lawn – you may want to scarify the grass before sowing new seed. Scarification lifts material from below the soil line and encourages new root growth. You can hire lawn scarifiers at reasonable prices.
  3. Once your lawn is prepared, follow packet instructions on how much seed to use. To make a useful ‘carrier’ for your grass seed, mix equal parts compost and sand in a bucket. Add your grass seed and stir to get an even distribution of all three materials.
  4. Make sure your grass seed mixture is moist, not dry.
  5. Spread the mixture evenly over the areas you want to seed.
  6. Avoid walking on these newly-seeded areas until your new grass seeds have firmly taken root.
  7. Water with a fine spray, to avoid dislodging and flattening the seedlings. If there is no rain, water every day for the first two weeks, but remember grass seed needs moisture to grow.
  8. Once you have seedlings that are about 8cm (3 inches) tall and well-rooted in the ground, cut the grass again. This will encourage your new grass to thicken up, stop old grass from swamping new seedlings and help to keep weeds down too.

How Long Does It Take for Grass Seed to Grow?

Once your grass seed is sown, and you are watering regularly, you should see new seeds emerging in about 10 days, or even earlier. How quickly your new grass grows all depends on the weather, the amount of moisture in the soil, your soil type and the types of grasses you are growing.

Nothing’s Growing – Should I Use Fertiliser?

If your seedlings seem to be struggling, you might consider using a lawn fertiliser. Before you reach for a quick fix though, check you have covered all the basics. Is the grass seed getting enough water? Is the weather scorching hot and drying everything out? Are there weeds smothering the growth of your new grass?

If you’ve got all of the above covered and you still see no new signs of life in the lawn, you might think about fertiliser. Choose a product that will improve the condition of the soil, and therefore your whole lawn. You can buy organic lawn food designed to be used in spring/summer or autumn/winter. This will help to feed and improve your soil, which in turn will help seedlings as well as your old worn-out grass to grow.

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Amit Kumar