You can improve the appearance of existing lawns dramatically by overseeding. New grass retains its green colour longer in periods of drought because of better rooting than the old sward. Weed invasion is also minimized as the sward gets denser. This will reduce the use of chemicals and is environmentally friendly.
The old sward will slowly die out over the years. By sowing new lawn seed into the existing lawn a technique used by professional groundkeepers and known as overseeding it is possible to rejuvenate the lawn. Overseeding can be done in spring or in early autumn. Early autumn is preferable as the soil temperature is high and moisture normally sufficient. At the same time there is less competition from the old sward towards the new young plants.
- Mow the lawn closely. Choose a time when the lawn is dry. Remove any rubbish from the surface of the lawn before mowing.
- Rake the lawn using a spring tine rake to remove and break up layers of dead matted grass or thatch. This process can be made easier using a machine.
- If the ground is compact it needs to be loosened to improve the root growth and the drainage. It can be spiked with a fork to a depth of at least 15 cm. This job can also be done by machine on larger areas.
- Select a suitable mixture of lawn seed. Ideally the mixture should contain the same species as the original old sward in order to avoid differences in appearance.
- Mix the seed and sow by hand or machine. To ensure an even lawn the seed should be sown in two directions at right angles. Mix the seed with sand to give a more even seed distribution. The seeding rate is approx. 4.0 kg per 100 m2. Make sure the ground is moistened thoroughly before sowing.
- Feed the lawn with a quality lawn fertilizer (high Nitrogen in spring low Nitrogen in autumn).
- To get a dense grass growth and to remove minor hollows it is recommended to top dress the lawn with a mixture of sand peat and loam.
- To improve germination the area should be raked. This ensures that the seed comes into contact with moisture and that the topdressing is worked into the grass. Lightly roll if possible.
- Irrigate if necessary with a fine spray keeping the seedbed constantly moist. After establishment irrigation should be restricted. Water between 30-40 mm at time to secure a deeper root system.
- Mow with a high cut when the grass is 40-50 mm. Trim lightly and gradually lower blades to an ideal cutting height of 25-30 mm. Mow regularly but try not to remove more than 1/3 of the growth at any time.