Can I start landscape plugs from divisions in summer?

Hi y′all, I′m planning a native meadow installation for the fall and want to start from plugs using a grass, violet and sedge matrix design like so. I′m thinking it would be most economical to just divide out plants already growing in my yard and pop them into deep landscape plug flats to develop roots until planting time (can be as late as mid-October). What I'm worried about is that it may be too late now to get the level of root development I want or even that it may be too hot for the plants to survive even in a greenhouse (hitting 90 most days and reasonable to expect at least one heatwave up to the low 100s in this lovely fossil- heated climate). That said…. the plants I′m after are literally weeds. Am I overthinking it? Help!