June - Warmer days and longer nights. summer is the best season for perennial favourites such as Achillea, agapanthus, aquilegia, astilbe, astrantia, campanula, cimicifuga, delphinium, dianthus, echinops, eryngium, foxglove, geranium, geum, hosta, iris, Jacob's ladder, lupin, leucanthemum, lychnis monarda, nepeta, poppy, penstemon, phlox, potentilla, thalictrum, veronica & viola.