Blue flowers rare? My friends might tell you it sometimes seems that's almost all there is. I am constantly growing trial plants to assay for blueness and pressing the results on all my gardening friends. True, there aren't as many as yellow and pink offer, but there are lots of true spectrum blues available, some brilliant and many stunning. Oddly, not many are fragrant, and most of those are bulbs.
I have read that most blue flowers are from the northern hemisphere; why that would be is a mystery to me. A bigger mystery is the reputation for rarity. Perhaps because so many pure blues are annuals that resent transplanting or perennials which don't readily bloom in pots, thus frustrating most garden centers; or perhaps it is because of nurserymen offering up lavender as though it were blue. We all fall for it. Catalog descriptions written by true believers or cynics with high-color printing lead us into purchases we sometimes rue. Here are things from my list of favorite 'true blues':
The very first are the forced reticulata iris from the fridge, in January if you remember in the fall soon enough (October & November). They smell wonderful & are marked with cheery gold & brown stipples and transplant out well later on. Next come the narcotically fragrant hyacinths; I always pot some to bring out the first week of March to break up the winter. 'Blue Jacket' are nice and this year I will try some 'Menelik' from Old House Gardens: so inky blue as to be nearly black, the catalog says; have to try them. Hyacinths also transplant well in the spring, blooming for years to come. Fast now come the blues out in the garden: reticulata iris, Muscari in several shades of blue, (try the powder blue 'Valerie Finnis'), hyacinths, and the little bulbs. Chionodoxa sardensis, a larger Glory of the Snow than the standard, bearing more and much brighter, deeper blue flowers on taller stems. Scilla siberica 'Spring Beauty' is best adored by lying on the sunny spring lawn with your nose up to them to inspect their pretty bells, blue pollen & shiny foliage and to enjoy their sweetness. If left to their own devices & the lawn mower is kept leashed, they will sow far out into the lawn. Violas and violets put on their show next. Viola 'Joker Light Blue' is indeed truly blue and is hardy here as a perennial, forming larger clumps over time and sowing very similar progeny. I would not be with out this tidy gem which blooms most of the year. Viola adunca, the Early Blue Violet, though teeny in the woods and modest, is lush and very bloomy in the garden, usually reblooming in the fall.
A nice combination the plants themselves thought of is Water Forget Me Nots (Myosotis palustris) with the double yellow primrose 'Sunshine Susie'. The regular forget me nots form a low pale blue cloud at the foot of my mother's cherry tree, perfect below the white blossoms and with double daffodils peeping out above the blue. Though the Water Forget-Me-Nots are rather rambling if they have the wet soil they prefer, I grow them in dryish shade and they stay put.
Mertensia paniculata, with its sky blue bells from pink buds and long stems of lilac-like foliage, will bloom till high summer if you put it in the shade; if the soil is rich it will pretend it is a bush, producing lots of stems for cutting. Dwarf bearded iris come on now in lovely pale blues and aquas; I put clumps as corner anchors in the raised vegetable beds to keep the lettuce company. They are soon followed by the very fragrant Orris root, absolute palest tissue paper-sky blue. Aril hybrid 'Mohr Pretender' is one of the best turquoise iris though perhaps a shy bloomer this far north. Dark blue I. cristata is a good scented ground cover in shady beds: I use it under tall primulas.
Lithodora I re-buy every few years as it isn't quite hardy here but has the kind of blue that makes you greedy. I pair it with a pale apricot perennial alyssum & wallflowers in copper.The Spring Gentian (G. verna) has big stunning cobalt goblet blooms & is easy to please in composty woodsy shade, and the early penstemon P. procerus has darling little deep blue flower cluster atop grassy spreading mats of deep green and is rather drought tolerant, especially if it's had winter snow cover. Tiny Alpine Forget-Me-Not, M. alpina, blooms here in the grass about then and you nearly need a hand lens to see the flowers--often the plants are only one to two inches tall.
Corydalis! Corydalis! My best luck so far is C. flexuosa 'China Blue', sweet scented and truly turquoise blue, snoozing by mid June and re-sprouting foliage in early fall. I also like C. Linstowniensis, purply blue and a heavy bloomer which takes the heat better, perhaps as it is tuberous. It is reblooming now in the end of September in our hottest year on record.
Meconopsis bloom the end of May-beginning of June, providing unbelievable electric blue poppies taller than me and furry donkey-ear leaves. Cool north side, please & no winter wet. Mine like being next to a French drain. The first time they bloomed we kept going out to gaze at them, like second helpings of ice cream.Siberian Iris are quick on their heels and range from palest to deepest blue and have a good range of heights. There are true blues as well as the blue-violets. I have been raising them from seed and it's fun to see the variations you get.Veronica has of course wonderful blues, too many to name here but I'll list three: V. 'Georgia Blue', cobalt bells atop ruddy foliage clumps to 10" or so; the taller bright royal blue 'Crater Lake Blue' with large flowers in bunches, good cut, and the mat forming silver-dusty V. tauricola, dotted in late spring with clear blue flowers.
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For instant gratification, nothing beats such annuals as cornflowers, larkspur, Phacelia campanularia (all of which hate transplanting; sow direct out or in pots) and the trailing Lobelias, plus my favorite, Morning Glories. Phacelia campanularia has velvety gentian-blue cups with big yellow anthers; it will bloom all summer and can make a lovely hanging basket.
The best Morning Glory is of course 'Clarke's Heavenly Blue'. A swag up across the porch, or over an east-facing window so you can look out through them as they open is not to be missed. Another good bet is 'Flying Saucers', true sharp blue striping with white in the manner of Rosa Mundi: irregular size stripes, no two blooms the same. The only other true-blue annual vine I know of is Lathyrus sativus azurea, a short climber with deep aqua blue flowers, often touched with rose in the heart. Not fragrant, but the color!
For sheer blue power, try Anagallis caerulea, deep intense blue inch or so wide blooms with a magenta-red eye if you look close. Their linear dianthus-like grey-green foliage makes a nice foil for the richness of the flowers and who would ever guess they are a cousin of primroses?And I always need Nemesia. 'Blue Gem' has sky blue flowers, 'KLM' has royal blue flowers with white tops, looking fake but good. (Its red sister 'National Ensign' looks even faker, but is a true red, & very showy.) Nemesias bunch out heavily and are very bloomy; a stem can fill a vase, and should, as they make good cuts.
Nigellas show their relationship to Delphiniums in their colors and in the little horns on the seed heads. N. sativa, 'Black Cumin', is good in the herb garden; its pale blue flowers are followed by spicy-fragrant (carrot? violet?) seeds which are lovely in baking & curries, or as an herbal pepper substitute. N. hispanica has larger, deeper flowers shading to purple and weird purple TV-reception looking stamens rising up in the center. Another spice by the way.
Baby-Blue Eyes is a good self sower and should be a requirement for the non-mowing lawn. Their frilly white-speckled foliage is nice in itself. Spring only but worth it. Older garden books show several other patterns, including stripes, which I haven't yet found. Another must for the non-lawn is Maiden Blue-Eyed Mary, Collinsia parviflora, tiniest intricate blooms on airy plants that flower early among grasses in my sandy soil but stay till mid-summer in the gardens. A local native, they have sown themselves for millennia I suppose on this glacial ridge and are accommodating themselves too, to the vegetable & herb beds I've built. Their blue haze makes me wonder why anyone would plant a lawn instead.
Convolvulus tricolor has bright blue ruffly flowers with white & yellow hand-painted looking throats. They reach about 8" and need rich soil to look their best and to be planted north of where you are standing; they face the sun and a bed south of the porch will just give you their backs. The mixed varieties include blues so pale as to nearly disappear. They add a nostalgic doily effect as a garden edging.Heliophila longifolia offers lovely mid blue flowers on long airy stems. They want to stand upright but end up sprawling; nice in planters or the window box but just won't behave in a hanging basket. Nice in arrangements, though.
Amethystia caerulea has a resinous scent and the whole plant gradually turns from green to steely cobalt blue. The tiny flowers are not showy but the scent & color keep on the dried foliage which is spiny like baby's breath. This deserves to be more widely grown; it is a good addition to planters or window boxes where it will be at nose-level or can be brushed for the scent which it keeps when dried. Sedum caerulea is quick to bloom and a fast grower. It covers itself with tiny starry blue flowers with teeny white edges. The effect is very delicate and the flowers smell of honey. Salvia patens, a tender perennial, has shocking, brilliant spandex blue flowers. Large flowers, too, and very pleasantly scented downy foliage, balsamic-lemony. Late summer bloom as an annual but tuberous rooted so can be wintered over.
Penstemons are amongst my favorite blues: tall, slender P. wilcoxii in the sky blue to lavender range, p. virens a diminutive look-alike, and p. nitidus, whose brilliant rich blue flowers resemble hyacinths. P. barbatus is available in several color mixes (mostly pinks & reds but with several good blues and violets tossed in) and will bloom its first year if started early, and then really put on a show in following years. Also good cuts. P. heterophyllus 'True Blue' is sky blue, but is fearsomely slow as an annual and a surprise if it returns to bloom here in a second year. Mid summer blues obviously include Delphiniums; I go for the lush Pacific Giants and British & New Zealand types, opting for as much flower as possible. A bed of mixed blues, footed with Penstemon barbatus in blues, purples & some hot pinks, is a rich treat. Some of the NZ blues, Royal Aspirations mix for example, include blues touched with purple and intense gentian blues, all with sturdy fat stems to stand up to wind and good for cutting.
Late summer and fall blues mean mostly Gentians and the willowy Salvia azurea which at about 4-5' resembles a sky blue phlox and flowers in late September to October. It is cold hardy & drought resistant but will lose its flowers with hard frost: I get 3 out of 4 years here; this year is a lucky one. Lobelia siphilitica's spikes of blues are more in the purple range really, like the Campanulas, but so reliable, tough and bloomy at such a late date that I count them here anyway. Gentiana septemfida & g. sino-ornata finish out the year, the latter ignoring frost until they finish flowering or the snow comes. Each is showier than the last, glimmering along their foliage like sapphires in the fall garden.