The best time to sow grass seed is in the spring (between late-March to May) or early autumn (between September to mid-October), however this is very much subject to the weather at the time.
Grass seed requires temperatures of around 10 degrees Celsius, or above, for a period of two to three weeks to germinate and start to establish, as well as adequate moisture in the ground.
The period between June to August tends to be too hot, with not enough moisture in the ground to establish. However, if the weather is mild and the seed is regularly watered, to keep ground conditions moist, then grass seed will germinate but the newly germinated seed will require continued regular watering until it is fully established. Due to the need of regular watering, this would not be suitable for larger areas but could be carried out in a garden.
During the period between November to February, the temperatures tend to be below 10 degrees Celsius and if they are higher than this, it tends to only be for a few days. As the temperatures are too low for the seed to germinate, the seed will rot. The ground conditions also tend to be too wet to prepare for seeding as well as the risk of waterlogged or frozen ground.
If possible, we would recommend spring time for any seeding as it offers the best conditions for the seed to germinate and you also get the continued growth and establishment throughout the summer period. If seeding in autumn, it is important to review the weather forecast for the coming weeks to ensure it is suitable for seed germination. Once the seed has germinated, it should be OK to survive the winter period but there is a risk that extreme cold temperatures could affect the survival of the newly germinated grass.