Plant your cotton seeds in the spring after the threat of frost has passed. Cotton does not mature well in cool temperatures, so wait to plant your cotton seeds until temperatures in your area stay above 60 degrees F.
Insert a thermometer 4 inches into the soil and monitor the soil's temperature daily until the soil averages 60 degrees F for 10 days in a row.
Sink the thermometer to a depth of 6 inches and check the soil's temperature at 8 a.m. every day. When the temperature holds between 58 and 60 degrees F for 3 days in a row, it's time to plant.
Begin your planting as early as possible because cotton requires a long growing season. Once you have the right soil temperature, quickly plant your seeds so your plants have plenty of time to mature before the harvest.