Grasses are generally lumped into two categories, warm season and cool season, depending on when they go to seed. Warm season grass flowers and then seeds in the warm months, somewhere between late summer and early fall, depending on the variety. Once it is mature, there are several ways to harvest grass seed. However, if the plot is small and you have patience, harvesting by hand is one of the simplest and cheapest ways to collect warm season grass seed for later use.
Wait for the grass seed to mature. In general, warm season grass matures between 20 and 30 days after its flowers emerge. However, it matures unevenly, so hand check the seeds for maturity at least once every few days.
Test a sample size of 10 seeds for maturity. Warm season grasses with large seed heads can also be tested by plucking off a few seed heads and striking them against your palm. If the seed heads shatter, they are ready to be harvested immediately.
Grab the base of the inflorescence or flowers with one hand, then run your hand upward to release the seeds from the grass and into the bag you are holding underneath it. Repeat until all the grass is harvested.