They are hardy so no need to keep them in a greenhouse over winter. As long as the roots have filled the pots you can put them in the ground now. Just ensure you work plenty of leaf mould/compost to mix into the soil in the planting hole.

Delphs are very prone to slug damage so I'd put a few pellets around each plant until the leaves die down, then again in spring before the new shoots break.

Thanks Bendipa