Is there a National Collection of blue flowers? There should be. It’s hardly a taxonomic distinction, but I can think of few plant characteristics that spring out at one as much as true blueness.
Just now it’s agapanthus. We bought a dozen bulbs at Chelsea last year for our new garden from a Yorkshire grower, half of them blue, half white. The blue have been flowering for six weeks now and are
still going strong, the white not at all, though their leaves are fine. The textbooks all agree that agapanthus need sun – though it seems they flower for longer without it. Most of ours are in our sunniest bed (still half-shaded), but those in almost total shade, three bulbs in a 12-inch pot, generously watered, are flowering best of all. Perhaps next year they’ll be all leaves and I’ll discover they did need sun after all.
Anemones, scillas, crocuses, campanulas, rosemary, geraniums, lithodora, ceanothus, nigella, clematis and hydrangeas have all given us blues of sorts. Recent sorties to Kew have added more salvias, morning glory and a passion flower too tender, I fear, for London to my list. But the really arresting blue of, for example, Salvia patens, is the gardener’s equivalent of the lapis lazuli renaissance painters reserved for the Virgin’s robe. It has long been my holy grail.