Lawn overseeding is exactly what it sounds like. It's sowing grass seed and overseeding on top of your existing lawn.
It is performed in the Mediterranean in the Autumn, to provide a new lawn of Cool Season grass lawn over the winter time when Warm Season grasses invariably change colour.
1) If your lawn is made up of cool season grasses, and have endured the stress of the summer heat, then autumn is a good time to overseed to bring back life to your lawn or fill in the brown patches.
3) Overseeding is also useful when planting grass plugs in the cooler months. The overseeding will produce a green lawn that will last all through the cooler and generally wetter months. We use overseeding in the winter months. The type of overseeding grass chosen is designed to die when the weather warms in the Spring/Summer, letting the warm season grass plugs take over.
4) Overseeding in the summer is also useful because this "nursery grass" will give a green lawn while the plugs knit together, thus reducing the possibility of new weed seeds taking hold.
You can also decide when you want the winter cool season (or nursery grass) grass to die by reducing the watering in line with the reduced requirements of the warm season grass, or at the point that you feel the grass plugs have knitted together.
The only drawback with this overseeding is that this technique although giving a green lawn throughout the winter, the lawn will require a little lawn mowing.
Before contemplating overseeding an existing old lawn, there are some preliminaries that should be attended to.
1) Test your soil, to identify any lawn soil pH problems, before you start.
2) Mow your lawn short.
3) Be generous with the seed.
4) After sowing, treat your lawn as if it were a new lawn, keep traffic to a minimum and change the watering regime for a few weeks until the new grass appears.