Between 50 degrees to 65 degrees Fahrenheit
Unlike perennial ryegrass and Kentucky bluegrass, Zoysia is a warm-season grass, meaning it germinates best when the temperatures are in the 70s or 80s. Typically germination time for Zoysiagrass seed is 10 days or more, so if you're not seeing growth by the time you hit the two-week mark, it's time to start worrying.  The basic requirements for germination of turfgrass seed are adequate moisture, favorable temperatures, and oxygen. The first step in seed germination is absorption of water (sometimes referred to as imbibition).  The germination of your grass seed depends very much on the species in the grass seed mixture that you choose, but it is generally relatively low maintenance to establish. Light and Oxygen it is important that grass seed is not planted. It needs to be spread on open soil and lightly raked to allow sufficient light and oxygen to get to the seeds. These are the necessary conditions for effective grass seed germination. Click here for our page on preparing a seed bed for a grass seed lawn. Several factors will determine the germination rate of grass seed. Air temperature, soil to seed contact, , presence and consistency of moisture and, age and quality of the seed.  Though seed will germinate at a wide variety of temperatures, the optimum temperatures for germination are in the table below. The temperatures listed are air temperatures which would be almost identical to that in on the surface of the soil barring radiation effects.  Cool season grass such as Fescue, germinate best when the soil temperatures are between 50&deg and 65&deg degrees F. These soil temperatures usually occur when the daytime air temperatures are between 60&deg and 75&deg degrees. The fescue grasses, when planted properly, germinate within 10 to 14 days. Now, most germination failure (especially with warm season grass) is because the grass seed was planted too early. Grass seeds have an outer shell (the hull) that prevents germination until conditions are right. Proper soil temperature is a big factor in the success you’ll have. For cool season grass, the ideal soil temperature is a minimum of 45-55 degrees (F). The perfect air temperature for spreading cool season grass seed is 60-70 degrees (F). A helpful tip: When choosing your grass seed look for the germination rate on the label. This is the percentage of seeds that germinated in lab tests. The higher the better. Usually planted in the early fall, cool-season grass seeds prefer daytime temperatures ranging from 60 to 75 F. With this temperature range, the soil itself is usually between 50 and 65 F -- the right environment for germination. If you have warm nights near 70 F, your soil is typically around that same temperature, making it perfect for seeding in the spring. Be aware that a particularly cool spring and summer may result in dormant grass and germination failure. Germination Failure. Grass seeds may fail if the temperatures aren't right for the particular type of grass. For example, warm-season grasses planted during a spring cold snap will stay dormant. As they lay in the soil, surrounding weed seeds take over the space and make it harder for the grass to become established. If you have warm nights near 70 F, your soil is typically around that same temperature, making it perfect for seeding in the spring. Be aware that a particularly cool spring and summer may result in dormant grass and germination failure. Keep in mind that some warm-season grasses, including some cultivars of bermudagrass and St. Augustine grass, don't do well when planted from seed. The soil temperature range for most warm-season grasses is between 65 and 75 degrees Fahrenheit and sometimes higher. Optimal air temperatures for warm-season grasses are 80 to 95 degrees Fahrenheit. If you plan to start your new lawn from seed, it is critical to know the best temperatures for seed germination.
http://www.allaboutlawns.com/lawn-maintenance-care/planting-and-repair/grass-seed-germination-is-yours-on-schedule.php http://plantscience.psu.edu/research/centers/turf/extension/factsheets/cool-season https://www.grassseeds.com/advice/grass-seed-germination/ http://lawncare.about.com/od/typesofgrass/qt/Grass-Seed-Germination-Rates.htm https://turf.purdue.edu/tips/2005/temp819.htm http://fescue.com/info/whentoplant.html http://mikesbackyardnursery.com/2014/05/grass-seed-germination-time/ http://homeguides.sfgate.com/warm-must-plant-lawn-grass-seed-67816.html http://homeguides.sfgate.com/warm-must-plant-lawn-grass-seed-67816.html http://homeguides.sfgate.com/temperatures-grass-seed-germination-61409.html
grass temperature germination