Please avoid introducing Phalaris in wild places where it is not already established, it's highly invasive and can easily crowd out native species. It's likely already growing near any stream, river, pond, or lake near you.
Wild grasses have a highly variable alkaloid profile expressing multiple phenotypes preferencing production of one or another alkaloid. Collecting from the wild will ensure a healthy mix of all of them. Not ideal for tryptamine specific seekers, great for full spectrum explorers.
As a source of tryptamines, you really want to seek out a cloned phenotype selected for tryptamine expression (named strains such as AQ1 or Big Medicine) or those with a consistent profile from seed (such as P. brachystachys or P. aquatica var. Australia). In order to ensure adequate tryptamine production within these varieties you will need to fertilize with high nitrogen fertilizer and harvest at roughly 7-14 day intervals.
If you truly wish to explore the wild grasses (or grow strains of unknown phenotype) there are a few things to take note of. Tryptamine production is highest in new growth and regrowth. Spring and summer, before the grasses flower, are when the grasses are producing tryptamines (also gramine). The literature reports a small tryptamine spike during flowering, I have not personally confirmed this. Post-flowering tryptamine production drops off entirely and the grasses shift to beta-carboline production.
My suggested protocol for wild grass would be to identify a patch as early as possible in the springtime via last years flower heads. Cut back and dispose of all last season's dead growth. Give it a week or two to put on sufficient new growth then come back and harvest that first spring growth. Come back every week or two weeks and harvest again (7 days will be higher in tryptamine content but less biomass, 14 days will be more biomass with a lower tryptamine content, or anytime within that window - maybe 10 days for a good balance). If possible freeze the harvested material while fresh, otherwise dry it for storage.
You'll likely want at least a kilogram dry (2 kilos fresh) before attempting an extraction. You will get a mixed alkaloid profile this is not a path to pure DMT. It would be wise to test any wild grass extract with a TLC kit or send it off for anlaysis prior to ingesting it.