Making and harvesting grass seed is a relatively simple process, but timing is crucial. Once the seeds are ready for harvesting waiting even one or two days can result in the loss of a large percentage of your crop. For the home gardener trying to grow and collect grass seed for personal use, this is not too much of a problem as long as the gardener checks the conditions of the seed heads on a daily basis.
Stop mowing your grass and continue watering it frequently, keeping the ground moist but not saturated.
Inspect your lawn regularly, looking for flowers to form at the tips of your uncut grass.
Continue monitoring the growth of your grass seed following flowering. Approximately 3 to 4 weeks after flowering your seeds should be ready for harvesting. The length of time required for your grass seed to mature depends on the type of grass you are growing and on weather conditions. Dry, hot weather shortens the ripening time, while cooler weather lengthens it.
Cut a stalk with seeds attached and slap the stalk against your open palm sharply. If 50% or more of the seeds fall off the stalk into your palm, then your seeds are ready for harvest.
Use hedge trimmers to cut the stalks of ripened seeds from the grass. Collect the cut stalks immediately and place them in a black plastic trash bag.
Lay the trash bag in a sunny area with the top of the bag open so that moisture can escape. Close the bag at night and open it again when the sun comes up. Allow the seeds to dry for 3 days.
Close the top of the bag with your hand and shake the bag vigorously to remove the seeds from the grass stalks.
Lay sheets of newspaper on a flat surface protected from the wind and carefully dump your grass stalks and loose seeds onto the newspaper. Turn the bag inside out to get all of the loose seeds. Use your thumb and forefinger to gently rub off any seeds that are still clinging to the stalks and discard as many of the stalks and chaff as possible.
Gently blow on the seeds and remaining chaff to separate the chaff from the seeds. Place the seeds in a clean glass container and seal. Keep the container of seeds in the refrigerator until it is time to plant your seeds.