Grass seed harvesting does not have to be a complicated task. The most important factor is waiting until the seedhead has matured before detaching it from the plant. Cut too early and the seed will not be viable and will not germinate. Take time to let the grass grow and the seedheads to fully mature, and you will be rewarded with plump mature seeds.
Stop mowing the lawn if you are trying to harvest a patch of lawn grass seed.
Allow the seedheads to develop completely until they are plump and drying out; typically it takes 20 to 30 days for seedheads to ripen after flowering.
Cut the stems of the seedheads 2 to 3 inches below the bottom of the seeds. Hold the seedhead carefully to keep the seeds from falling out.
Place the whole cutting into a paper bag. Loose seeds will fall to the bottom of the bag. The seeds that stay in the seedhead will continue drying until they are ready to fall out.
Store the closed bag of collected seeds and seedheads in a cool and dark place away from the danger of pests. Shake the bag vigorously after six to eight weeks. Pour out the seeds into a container. Remove the extra plant material and store the grass seed in an airtight container. The seeds should be ready to use the next growing season.