We can take our cue from nature. Most perennial plants and many annuals can be sown at the time of natural dispersal of the parent in the wild.
In the case of perennials start them off now and under protection from the worst of the winter weather, your babies will have a real head start come spring. They’ll almost undoubtedly flower next summer. So if you can protect them, they’re pretty hardy anyway, don’t wait until spring to sow, sow up until the middle of September, or even the end depending on the weather.
Annuals can also be sown now in situ if you have a patch of well worked soil, that will stay mostly weed free until they emerge in spring, go for it. Otherwise keep until early spring.
Biennials are a bit different, to get them to a good rosette size they needed to be sown from early spring up to June time and then they’ll flower in the next year.
In short now is the time to sow perennials, happy sowing 🙂