What next for my tiny plug perenniels?

Pot them on when you can see the first roots through the holes in the bottom of the pots, then grow them 'hard'. In other words, outside is better than in your greenhouse. If there's a nasty winter (!) you might have to provide protection and take them into the greenhouse with fleece over them, as they would freeze in pots.

I assume they're all hardy ones??

Thankyou. I am officially at war now with the slugs...who also want to eat these tasty baby perenniels. Yes they are hardy. Delphinium,galliardia,achinachea,lupins,aubretia, verbena.

Oooh, yes - slugs (and snails) love those - especially the Dephiniums and Lupins! You'll have your work cut out. Good luck!

you may get them big enough to plant out in the early autumn. they are more likely to survive a harsh winter in the ground than in their pots. {I know from bitter experience !!}

Thanks for that. How big is big enough? They have grown an incredible amount since last week. They are two to four inches inchs tall now and glowing with health. I have created a new bed which I could almost use as a nursery bed, and thin later ? Any experience of planting small perenniels out during the summer, what do I need to know ?

wait till they are about 6 inches then plant them in the new bed in their final positions. They will soon fill the gaps or you could put annuals in to fil the gaps.
with any new plants make sure the soil is well dug, enriched with compost/growmore etc. firm plants in and water well. keep an eye on the watering for at least a month if not much rain [or longer if really dry]. For taller varieties pop their support stakes in at the same time so they grow and are supported.

hope this helps.

Thanks all...