Existing lawns can be improved 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 more dense. Overseeding can be done in spring or in early autumn:
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The first step is to mow the lawn closely. Choose a time when the lawn is dry.
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Rake the lawn using a spring tine rake to remove and break up layers of dead matted grass or thatch. The process is known as scarifying/verticutting and is easily done using a machine.
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If the ground is compact it needs to be losened. It can be spiked with a fork to a depth of at least 15 cm. This job can also be done by a machine on large areas. This will improve the root growth and the drainage of heavy soils.
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Select a suitable mixture of lawn seed. In principle the mixture should contain the same species as the origin of the old sward in order to avoid differences in appearance.
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Remix the seed and sow by hand or machine. The seed should be divided into 2 portions, one portion to be sown in one direction, the other portion to be sown crosswise of the first portion. The seed can be mixed with sand in a bucket in order to give a more even seed distribution. The seeding rate is appx. 2,5 kg per 100 m2. Ideally the seed should be sown after the ground has been well moistured by rain. This will give the seed adequate moisture to start with.
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Feed the lawn with a quality lawn fertilizer (high Nitrogen in spring, low Nitrogen in autumn)
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The lawn can be top dressed with a 3-5 mm layer of a mixture of sand, peat and loam - proportions will be dependent on soil type - 3-5 mm layer. This will result in denser grass growth and removal of minor hollows.
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Rake the area so that the seed is in contact with moisture and the topdressing is worked down into the grass. This will improve germination. Lightly roll if possible.
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If dry weather follows overseeding, irrigate with a fine spray keeping the seedbed constantly moist.
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When the grass is 5-8 cm the first mowing can be done with a high cut. Trim lightly and gradually lower blades to an ideal cutting height of 3-3,5 cm. Mow regularly but try not to remove more than 1/3 of the growth at any time.
