Source: The Castaic, CA weather data displayed above is derived from the NOAA (National Oceanic and Atmospheric). Air quality and pollution data is derived from the EPA (United States Environmental Protection Agency). Air quality and pollution levels measured in a particular area may not be representative of the entire county.
Plant fescues when fall temperature reach about 75 F. The next best time to plant fescue seeds is when rising temperatures in spring reach 60 F. Summer isn't a good time to plant fescue lawns, because fescue grass tends to go dormant during periods of high temperature.
Since tall fescue is a bunch type grass and does not spread, it is necessary to overseed occasionally to maintain turf thickness. The best time of the year to overseed is in the fall. This gives the seed time to germinate, grow and develop sufficient root depth before the summer heat arrives in the following year.