Growing lomandras from seed can be rewarding but does require patience.
The general approach is to collect seed over the summer, sow seed in autumn and wait for eventual germination which can start after two or three months and continue over two or three years, sometimes with waves of germination.
First, collect ripe seed. Collect seed when some of the capsules have already opened. Generally this is from November to January. Later collections are possible including seed collection from the ground around the plant.
Keep the seed till autumn of the same year or next year. Begin the treatment of seed with cold stratification (seed on moist paper in the fridge) for one or more months. Then soak the seeds in water for at least 24 hours. Soaking can be done for up to about ten days changing the water every day. Then soak the seeds for 3 days in a solution of gibberellic acid (1,000 mg/L). The seeds are then ready for sowing. Expect some germination at 4 weeks with more at 8 weeks. Keep the seed tray for successive germination some of which may occur as a burst in 12 months.
Tube up seedlings when at least 20 mm. I have begun using a medium of 2 parts BioGrow to one part propagating sand. Plants tubed up before the end of year should be ready for planting in the following winter.