I'm sure the timing isn't that precise. I'm sowing perennials now as seed ripens. Perennials take longer than annuals to get going (mostly) so I always start them in pots and grow them on a bit before planting out. In my garden they could easily be overcome by weeds or dislodged with the weeds.
I'll leave it to those who will scroll up and down trying to work out which number is which plant. I've gone cross-eyed already
Philadelphus another possibility
if Buxton Blue was pink it would be called Buxton Pink,
Very few plants are really true blue, but Buxton Blue is on the blue side of mauve.
I'd look at something like Vicia sepium, Bush Vetch. Pea family pretty blue flowers, clambers through shrubs. Might be worth letting some grow to confirm. But not a hypericum or periwinkle for sure, the arrangement of the leaves in the stem is all wrong.
can you do a bit of digging and see if they're all joined together underneath the ground?
I saw one of those in a GC today. Thought it needed watering then saw the name. Left it where it was, I don't want pre-wilted plants.
looks like some sort of pea to me.
Are there any in a more advanced state than that, what plants are in the area?
looks like Mugwort, Artemisia vulgaris.
I don't think they grow again from the tops. Don't let him/her loose again.
Bamboo is best reduced by completely removing some stems and leaving the rest.
If the plant is too tall, it's the wrong plant for the situation.