Overseeding can be used to thicken a lawn or to change the mix of grasses present to more suitable ones for the conditions. In order for the seed to germinate and survive, preparation and aftercare must be carried out properly.
Grass seed germinates in warm conditions, (above 6 degrees, soil temperature) when it is kept consistently moist. If it gets wet, then dries out, germination will fail. A good tilth, or crumbly soil, will enable the seed to hold the moisture and also get a foothold with its roots. We prepare the soil by scarifying and setting the blades just below the soil surface or by using a spring tine rake and some elbow grease! Use a good amenity seed.
Beware of grass seeds that claim to be shade resistant or better performing during drought. This does not mean that it will grow in full shade or with no water! A normal overseeding rate we use is from 25g per sqm to 36g per sqm. Better germination will be achieved the more seed that is sown. We sow enough to keep everyone happy: some for the birds, some for “damping off” and the rest to germinate.
If the area to be overseeded is small you may want to cover it with chicken wire or similar, however, providing the preparation has been good and top soil layer is covering most of the seed your rate of germination should be sufficient.
Once germination has been achieved the soil needs to be kept moist so that roots can develop. Water little and often and as the seedlings develop, encourage to them forage for water deeper into the soil profile by watering less frequently without letting the lawn dry out.
Don’t allow the new seedlings to get too long and straggly. Instead cut the lawn to encourage thicker growth.