Blue is one of the rarest of floral colors; only black is more elusive. And that’s probably because of the complex chemistry involved in producing a blue pigment, because bees, butterflies and other pollinators actually find blue quite attractive and easily visit blue flowers. That means that, evolutionarily speaking, blue flowers should be a good choice for blooms and flowers ought to have evolved as readily in that direction as they did towards the pink, white and yellow flowers that are so common.

But it turns out blue is hard to produce. The blue in flowers comes from a pigment that normally gives red or purple hues: anthocyanin (from Greek meaning dark blue). Various forms of it as well as related chemicals give flowers their blue coloration. But most plants with reasonable quantities of this compound produce purple to red flowers instead. Why?

Well, that’s complicated. Suffice it to say that various molecules and metal ions have to be present and also the environment near the pigment cells has to be alkaline. Many plants with true-blue flowers (notably in the families Boraginaceae and Convolvulaceae) have pink buds that turn blue as their environment becomes more alkaline, but most anthocyanin-rich flowers have acid sap and therefore their flowers turn out purple or red. In flowers, blue is a co-pigementation: it needs the right conditions to express itself.

Blue Flowers Are Highly Desirable

Blue flowers are much appreciated in the florist industry, so much so that dyeing or spraying white flowers blue to make them more saleable is a common practice. Dyes are even injected into living plants to give a blue tint to their flowers. That’s the case of the blue orchids that are so often seen on the market these days. They are actually blue-tinted Phalaenopsis and the next time they bloom, the flowers will be white.

There are scientists all over the world working to introduce genes for blue coloration into popular cut flowers—roses, carnations, chrysanthemums, etc.—with, so far, only mitigated success.

The efforts to create a blue rose (Rosa) by transferring genes from blue-flowering plants into hybrid tea roses have resulted in a so-called blue rose, Applause, launched by Suntory in 2009 … but in my opinion, it’s not really blue. It’s closer to lavender. Of course, that is an exciting new color for roses, but the true blue rose has yet to be created.

The same played out for carnations (Dianthus caryophyllus). Scientists transferred genetic material from blue-flowered plants, plus deleted carnation genes that were hindering the coloration. The resulting “blue” carnations (all those that I know of belong to the series Mooncarnation) are actually different shades of purple and violet. Now, these are new colors for carnations, of course, but they certainly aren’t blue.

Very recently (July 26, 2017), scientists announced the creation of the first blue chrysanthemum (Chrysanthemum x morifolium). It was obtained by inserting genes from a bellflower (Campanula medium) and a blue pea (Clitoria ternatea) into a chrysanthemum. Again, these new mums are being touted as true blue, but I still see a lot of lavender in the flowers and would definitely not call them blue.

Note that these manipulations are all examples of genetic engineering. In other words, these plants are GMOs, a term that scares the s___ out of many people. That said, blue roses and blue carnations have been on the cut flower market for a decade now and I have yet to hear any outcry.

True Blue Blossoms

Obviously, there are true blue flowers, and in fact they evolved all on their own and have been around for millions of years. I don’t think anyone will deny that a ‘Heavenly Blue’ morning glory (Ipomoea tricolor ‘Heavenly Blue’) is blue. Moreover, this cultivar was not developed in a laboratory nor is it even a hybrid. Instead, it’s a selection of the wild I. tricolor, a species with naturally blue flowers.

And that’s just one example among many … well, among “quite a few.” There are probably no more than a few hundred true-blue flowers among the some 400,000 plants on this planet.

How to define “blue”?

In horticulture, there is a long tradition of claiming any flower even the slightest bit close to blue as being a blue flower. Above all, violet-blue flowers—definitely more violet than blue!—are universally called “blue” and violet is an abundant color in the floral world. I’ve always felt this was a case of wishful thinking: we’d like to have blue blooms, so we accept anything close to blue as being true blue.

This seems to be a worldwide phenomenon, by the way: in all the languages I know (4), purple flowers are regularly called blue. Linnaeus himself, the father of botany, named many violet-colored flowers coerulea, which means blue.

Also, I suspect the definition of blue varies from one individual to another. As I researched this article, I realized that I take a rather narrow view to “true blue”. I tend to apply that term to lighter blues (cyan, azure, sky blue, etc.), while to my eye, shades that could be considered blue (indigo, cobalt, etc.) are violet. I’m not sure everyone would agree!

Obviously, we could take the scientific definition of blue as a benchmark. Blue is caused by light rays ranging from 450 to 500 nanometers … but who has a device capable of measuring that?

True Blue Flowers

Here are some flowers that, in my eyes, are true blue. I’ll admit it’s a subjective choice, but—hey! —I am the one writing this article!

1. Allium caeruleum (blue globe onion) – bulb, zone 3
2. Amsonia spp. (bluestar) – perennial, zone 4 to 6, according to species
3. Anagallis arvensis (poor man’s weather-glass) – annual
   

   Borago officinalis. Photo: Sten Porse, Wikimedia Commons

4. Borago officinalis (borage) – annual herb
5. Brunnera macrophylla (Siberian bugloss) – perennial, zone 3
6. Centaurea cyanea (cornflower, bachelor’s button) – annual
7. Ceratostigma plumbaginoides (leadwort) – perennial, zone 6
8. Clitoria ternatea (blue pea) – tropical climber, annual
9. Commelina communis (dayflower) – annual weed
   

   Corydalis flexuosa. Photo: jardinierparesseux.com

10. Corydalis flexuosa (blue corydalis) – perennial, zone 6
11. Cynoglossum amabile (Chinese forget-me-not) – annual
12. Eryngium spp. (sea holly) – perennial, zone 4
13. Evolvulus x ‘Blue Daze’ (compact morning glory) – annual
14. Hydrangea macrocarpa (blue hydrangea), blue in acid soils – shrub, zone 6
15. Ipomoea tricolor ‘Heavenly Blue’ (morning glory)—annual climber
16. Linum perenne (perennial flax)—perennial, zone 3
17. Linum usitatissimum (common flax) – annual
    

    Meconopsis betonicifolia. Photo: Andrew Curtis, Wikimedia Commons

18. Meconopsis betonicifolia (blue poppy) – biennial or short-lived perennial, zone 3
19. Mertensia spp. (Virginia bluebells and others) – perennial, zone 4
20. Myosotis spp. (forget-me-not) – biennial, zone 3
21. Oxypetalum caeruleum (tweedia) – annual
22. Plumbago auriculata (blue plumbago) – tropical climber or houseplant

Flowers That Are Often Blue

The following plants come in a wider range of colors, including many violets and purples, but also some true blues. With these variable plants, if you want blue flowers, make sure you pick the right cultivar.

1. Delphinium spp. (delphinium, larkspur) – perennial or annual, zone 2
2. Gentiana spp. (gentian) – perennial, zone 2 to 6, according to species
3. Eustoma grandiflorum (lisianthus) – annual
4. Hyacinthus orientalis (hyacinth) – bulb, zone 4
5. Iris x germanica (bearded iris, garden iris) – perennial, zone 3
6. Lobelia erinus (edging lobelia) – annual
7. Lupinus spp. (lupine) – annual or perennial, zone 3
8. Muscari spp. (grape hyacinth) – bulb, zone 3
9. Salvia guaranitica (blue anise sage) – annual in cold climates
10. Salvia patens (gentian sage) – annual in cold climates
11. Viola x wittrockiana (pensée) – biennial or short-lived perennial, zone 4

So-Called Blue Flowers

What follows is just a short list of plants many gardeners consider to have blue flowers, but that, personally, I find too close to violet to belong in that group. So if you’re planning a blue border, you might want to skip these.

1. Aconitum spp. (aconite, monkshood) – perennial, zone 3
2. Agapanthus spp. (lily of the Nile) – summer bulb or perennial, zone 7
3. Ageratum houstonianum (flossflower) – annual
4. Anchusa spp. (bugloss) – biennial or perennial, zone 3
5. Aquilegia coerulea (blue columbine) – perennial, zone 3
6. Browallia spp. (browallia, amethyst flower) – annual
7. Campanula spp. (bellflower) – biennial or perennial, zone 3
8. Echinops spp. (globe thistle) – perennial, zone 3
9. Geranium spp. (hardy geranium) – perennial, zones 2 to 9, by species
10. Hyacinthoides non-scripta (bluebells) – bulb, zone 4
11. Iris sibirica (Siberian iris) – perennial, zone 3
12. Iris versicolor (larger blue flag iris) – perennial, zone 3
13. Lobelia siphilitica (great blue lobelia) – perennial, zone 3
14. Scilla siberica (Siberian squill) – bulb, zone 3