When is the best time to plant Perovskia? Can this be planted out now (September)?
Assuming this to be a pot-grown plant , now would be a good time ; the ground is still warm enough for it to develop a root system and semi-establish .
Yes. Stand its pot in a bucket of water till no further air bubbles appear then remove it from th epot, tease out its roots and make sure you plant it at the same depth as before and improve its soil with some well-rotted garden compost or planting compost. Water in well and keep it watered if you have a dry spell. Once the autumn rains set in it should be fine.
You can help it along by sprinkling some bonemeal in the new hole and soil to encourage root development and, if you have some, a little microrhizal fungae sprinkled directly on the roots to help them establish. Prune the stems back in spring, when heavy frosts are not forecast, and then feed it some pelleted chicken manure to encourage plenty of fresh new stems withe the characteristic silvery foliage and blue flowers.
Thanks Paul B3 and Obelixx - will follow instructions and get them planted tomorrow