How to Overseed a Lawn with Grass Seed

Good soil contact is essential, so follow our over-sowing procedure to make your lawn better than ever in as short as possible.

Overseeding an existing lawn with grass seed requires much more attention than seeding a new lawn.

How Much Grass Seed?

When you have chosen your grass seed, check the recommended overseeding rate on the packaging. This is usually lower than the rate for starting a new lawn, but in some cases, adding more seed that contains ryegrass can speed up recovery. If you’re changing the grass type, then using a higher seeding rate will make a more significant impact.

Don’t assume more seed is best, though! Using too much seed in patch repairs where the soil is barely visible can lead to dense growth that stands out. As a rule, aim for 10 to 20 seeds per square inch.

Over-seeding Procedure

Prepare the Soil

If the lawn is relatively dry and rain is unlikely, start building a reserve of water in the soil by running the sprinkler for an hour or two a day for several days, depending on how dry it has been. You don’t need soggy ground, but seeds and seedlings need water to germinate and root. This should be done after renovating (raking, scarifying or aerating) but before seeding and fertilising.

Mow the Lawn

Cut the grass short before overseeding but avoid scalping the lawn.

Spread the Seed Evenly

Spread the seed by hand or using a seed spreader in a different direction for each lot, e.g., north to south, then south to north, east to west, etc. This will ensure even coverage. A smaller than recommended setting (say 1/3 to 

(1/2 open) on the spreader will prevent you from running out of seed too quickly, but it will also mean more trips up and down the lawn.

Seed-to-Soil Contact

If there is quite a lot of grass sticking out of the lawn after scarifying, then the seed you are adding will stick on it, preventing contact with the soil – not good. If you can, drag a garden hose, a piece of wire mesh fencing or a large brush over the lawn to knock the seed off the grass and into the soil.

Roll the Lawn

Next, roll the lawn. If you don’t have a roller but a lawn mower with a roller, this will do just fine. It might be best with the engine off, though! If you don’t have either and the lawn is not too big, start treading up and down the lawn. Good seed-soil contact will improve the result greatly.

Fertilise

Now fertilise the lawn using a seasonal fertiliser to benefit the old and new grass. Fertiliser can be added at any point in the above procedure, but for convenience, it is done at this stage. However, if you doubt that conditions may turn against you (dry or cold), fertilise once the seed has germinated.

Watering the seeds

If possible, give the seeds a light watering as often as possible every day for a couple of weeks if there is no rain. Enough to keep the seed from drying without washing it away. If watering is impossible, schedule your seeding for a wet period. In dry conditions, covering the area (after building a reservoir of moisture) for 10-14 days with large sheets of polythene available from builders and merchants is a very sensible. No watering during this period will be required. Nice!

Watering as Grass Grows

Once the seedlings are a week old, water less frequently but for twice as long. At about the 4-week mark, water twice weekly for about 15 minutes anywhere. After 8 weeks, water more deeply to ensure the lawn doesn't get overly dry. See our guide on Watering the Lawn.

Mowing

Unlike starting a new lawn, you should mow your lawn as usual. However, to reduce stress on the new grasses, mow at least weekly for the first 2 months, no lower than 1” and preferably at 1.5″ to 2″, with sharp blades on dry grass.

NOTE: Because grass seed is elongated, it does not consistently ‘flow’ through rotary or broadcast spreaders. Though a seed spreader is an excellent method, its settings are unreliable. We suggest starting with a one-third open setting and applying it in several lots to ensure consistent, even coverage.