Like many gardeners, I have a “thing” for blue flowers. Lobelia (below), Blue Mist Spiraea, cornflower (Bachelor’s Buttons), and Borage all find a spot in my garden. I’d love to include Himalayan Blue Poppies, hydrangeas, and morning glories but they don’t do as well in my soil and climate. (The poppies need constantly damp soil, hydrangeas need acidic soil to turn them blue plus they’re not hardy enough. The morning glories do well in my greenhouse, but outdoors they usually freeze before them get around to blooming.)
Surveys tell us that blue is by far the most popular “favorite color,” which may explain why blue flowers get so much attention. I think a better explanation is our penchant for anything rare, and blue is a rare color when it comes to blooms. In fact, only 10% of flowering plants produce blossoms in shades of blue. Why is that?
It turns out that plants have to perform all sorts of biochemical manipulations to produce the color blue. There are no blue pigments. (This is also true with birds such as the various blue jays and bluebirds, whose blue color comes from the way the feathers are structured.)
Instead, plants make red pigments, which are then chemically altered to look blue. It takes a lot of work from the plant’s point of view, and is of dubious benefit. Bees and other pollinators can see blue, but they see other colors as well. From a natural selection perspective, there’s no real advantage to being blue.
Plant breeders see this as a challenge, and go to great lengths in their attempt to produce blue versions of familiar flowers. Now that it’s possible to manipulate a plant’s biochemistry, they can introduce delphinidin, the chemical that makes delphiniums blue, into other species. Unfortunately, often the results are disappointing. For example, in spite of years of effort, we have roses that are violet-purple, but not blue.
This leads us to one of my pet peeves—the horticultural habit of calling flowers “blue” when in reality they’re some shade of purple. (Now that we understand the link between red pigments and blue color, we can see why these flowers are purple.) I’m tired of getting all excited about ordering seeds, or buying a perennial out of bloom, expecting true blue flowers, only to find out much later that I’ve lavished my time and money on yet another violet or lavender flower. Why the misleading descriptions? Why can’t gardeners just use the color names we’re all familiar with?
Assuming that by blue, we mean blue, what are some blue flowers that do well in Colorado gardens? I’ve mentioned several already: Lobelia, cornflowers, and borage are annuals, while Blue Mist Spiraea is a sub-shrub (it has woody stems but blooms on new growth, so you should cut it back each year). Nigella (aka Love in a Mist) is another annual with blue flowers.
No list of blue flowers would be complete without Delphiniums. They’re sufficiently hardy, but prefer a bit more humidity than is normal for Colorado—how they do depends largely on the specific microclimate where they’re planted. If your garden is too dry, try some sage instead. Perennial Salvia azurea and S. patens are both hardy and drought-tolerant.
Pulmonaria (Lungwort) is a good choice for shade. Its diminutive pale blue flowers decorate plain or spotted leaves on low-growing perennial plants.The Colorado wildflower Mertensia (Chiming Bells) has blue flowers that turn pink when pollinated. A bit taller than Pulmonaria, Mertensia also appreciates shade and moist soil.
A much taller (2 to 3 feet) perennial with clusters of very pale blue flowers, Amsonia is a little-known flower that is growing in popularity. Finally, Siberian Squill is a “minor” bulb with pale blue star-shaped flowers. It blooms very early, often in late winter.
Blue flowers are easy to incorporate into a landscape. You can either combine them with pink, lavender, and white flowers, silver foliage, and other cool, complementary hues for a calm effect, or use them to set off the high-energy, vibrant contrasting colors of yellow and orange. Either way, every garden needs blue!
Flower photos, from top: Himalayan Blue Poppy, Lobelia, Nigella, Salvia azurea, Delphiniums, Mertensia.