This also came up before, but worth repeating in this busy planting season.
Everybody, everywhere tells anyone who’s listening that plastic pots, flats, and inserts should never be re-used without first disinfecting them in a bleach solution, lest pathogens be spread to the next crop you’re seeding. They all say it, I swear. Makes sense. But then, never having time for that, and hating the smell and soapy feel of bleach, I used to leave them outside to let sunlight disinfect them, but they’d blow everywhere and Bride didn’t like the look of plastic trays all over the yard, so that didn’t work.
Then the novel thought occurred to me, “How are flats and inserts going to spread disease to new plants if the old ones weren’t diseased?” Duh.
So now I’ve been re-using old plastic flats and such for years, until they wear out, with never a problem. The only ones I absolutely will never re-use without disinfection are those from other nurseries and garden centers. Mine, yes. Theirs, never.