Seeking the True Blue Flower



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

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These orchids have been dyed blue. Photo: Tangopaso, Wikimedia Commons

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.

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The Applause rose has “blue genes”, but looks dark lavender to me! Photo: Blue Rose Man, Wikimedia Commons

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.

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To me, these “blue carnations” from the Mooncarnation series are violet. Photo: Pagemoral, Wikimedia Commons

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.

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Newly introduced, this “blue chrysanthemum” is not yet commercially available. It’s closer to blue than blue roses and blue carnations, but still, it doesn’t look quite blue to me.  Photo: Naonobu Noda/NARO

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

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Ipomoea tricolor ‘Heavenly Blue’: now that’s a blue flower! Photo: Russel E, Wikimedia Commons

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”?

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Bluebells (here, Campanula cochleariifolia), are not really blue, but violet. Photo: Jerzy Opiola, Wikimedia Commons

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!

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Allium caeruleum. Photo: col&tasha, Flickr

  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

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    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

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    Corydalis flexuosa. Photo:

  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

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    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.

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Delphinium ‘Blue Fountains’: this mix from seed contains blue flowers, but also purple and white blooms. Photo: J.W. Jung Seed Co.

  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.

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Ageratum houstonianum ‘Blue Hawaii’: a pretty shade of violet, but not blue. Photo: Swallowtail Garden Seeds

  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 320170829A

Non-Stop Bloom with No Effort!


The first annual flowers only bloomed all summer if deadheaded.

Annual flowers have been popular since the mid-nineteenth century when gardeners discovered that these plants had the ability to bloom all summer… if they removed their faded flowers regularly, a technique called deadheading. If they let the annual “go to seed”, its flowering ended quickly, but if they cut the fading flowers off, it would continue to bloom until September.

That’s because, when a wild plant begins to produce seeds, this usually stimulates the production of a hormone that tells the plant to stop blooming and to instead devote its energy to seed production. However, if you remove the flowers before this signal is sent, the hormones that stimulate flowering continue to circulate. That’s why for generations gardeners have grown accustomed to deadheading their annuals in order to ensure bloom all summer.

But today’s annuals are not the same as those cultivated in 1850. To start with, many new annuals have been added to the home gardener’s palette since then, including a few that are naturally long- or even everblooming, such as wax begonias (Begonia x semperflorens).

But above all, most of the old-fashioned annuals have changed considerably over the years: in color, size, shape… and habit. By always harvesting the seeds of the most floriferous plants, generation after generation, gardeners have slowly developed varieties that rebloom whether they are deadheaded or not. Thus the majority of modern annuals – zinnias, cosmos, pelargoniums, etc. – flower abundantly all summer and few need any deadheading.

Still Evolving

And the situation continues to improve yearly.


‘Matrix’ is a heat-tolerant pansy that can bloom all summer.

For example, have you tried one of the modern strains of pansy (Viola x wittrockiana) lately, such as those in the series Panola, Matrix, Dynamite or Universal Plus? Where older lines stopped blooming when it became too hot only to to resume in the autumn, with the return of cooler weather, modern lines continue to flourish, often right up until frost, not slowing down in the least.

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Petunia Supertunia® Pretty Much Picasso® is pretty much everblooming! Source: Proven Winners

Another plant that has recently switched to the non-stop-bloom-without-deadheading category is the petunia (Petunia × atkinsiana). And that’s excellent news, because removing faded flowers from petunias, with their disgustingly sticky stems, was never much fun. Self-cleaning petunias that bloom continuously without deadheading have been on the market for about five years now and are beginning to push the old varieties out the door.

You’ll discover that seed companies are gradually replacing older varieties well known to gardeners with look-alikes that bear the old name plus “Improved” or “Select.” Or sometimes, they don’t even change the name, but simply sell the improved variety under the original name. Yesterday’s Supertunia® line, for example, needed a serious clean-up in mid-summer, but the Supertunias you find on the market today just go on and on.

Before buying a petunia, always ask the seller for a variety that doesn’t need deadheading.

And until only a few years ago, I still used to advise gardeners to cut back sweet alyssums (Lobularia maritima) and edging lobelias (Lobelia erinus) back by half in the middle of summer, just as their flowering started to weaken. This reboots their “time to flower” hormones, stimulating them to bloom anew and ensuring flowers for rest of the summer. But since 2009, I no longer give the same advice.


Sweet alyssum ‘Blushing Princess’ blooms from April to December without any pruning.

That was the year when the first hybrid sweet alyssums (Lobularia x hybrida) reached the market. These plants (found in such series as Knight, Princess and Stream) bloom faithfully all summer and beyond, almost until Christmas, without any deadheading or pruning. That’s because these new sweet alyssums are sterile and, since they produce no seeds, don’t receive the usual hormonal signal telling them to stop flowering, Instead they devote their energy to flower production. Thus they bloom on and on until frost kills them.


Hybrid edging lobelia ‘Techno Heat Electric Blue’

At about the same time, the first hybrid edging lobelias (Lobelia hybrida), also sterile, came on the market, including the series ‘Lucia’, ‘Laguna’, ‘Techno Heat’ and ‘Waterfall’. And again, since they don’t receive the hormonal signal to stop blooming, they also flower all summer.


Opium poppies won’t rebloom whether you deadhead them or not.

There are still some exceptions to the rule that modern annual bloom all summer even without deadheading. Annual poppies, like the Shirley poppy (Papaver rhoeas) and the opium poppy (P. somniferum) flower only once, at the beginning of summer, whether you deadhead them or not. And larkspurs (Consolida spp.) do the same. But these are exceptions to the rule. Today, it is clear that the vast majority of annual garden bloom will all summer, even if you don’t remove their fading flowers.

Hard to Convince Workhorse Gardeners


The workhorse gardeners like to remove spent flowers, even when it gives not results.

Obviously I’ll never convince the hardest-working gardeners to stop deadheading their annuals: they are so convinced that gardening is hard work, they simply never believe me when I suggest it doesn’t have to be so.

However, if you have just a few laidback gardener genes flowing in your veins, try the following technique this summer just to see. Plant your annuals, then sit back and watch them grow and bloom, getting up only to water them in times of drought. You’ll be amazed to see most of them bloom all through the summer without any effort on your part!