Phormium tenax - best sown fresh, barely covered, @55-65F. Germination in 30-180 days.

The hybrids like the one you mention are generally vegetatively propagated - genetically identical to their parents. Not so with seed raised plants  the seedlings will all be genetically different - will produce plants with an assortment (of genes!) of foliage colors, heights

I am interested in growing a number of grasses from seed, after I remove the seed from the plants do they need to be stored a particular way until next year or can I plant them now.