Get It Growing: Horticulturist says blue blooms are rare

By DAN GILL

LSU AgCenter

horticulturist

Blue, particularly true blue, is a color relatively rare among garden flowers. Blame the pollinators. Remember, flowers are not produced by plants for our enjoyment.

Many plants must attract pollinating organisms, such as insects or bird, to visit their flowers and carry pollen from flower to flower. The colors of the petals are strictly based on what will most effectively attract pollinators to visit the flowers and help with pollination. So how does this explain the rarity of blue flowers in nature? Apparently, blue is not that attractive to most insects and birds.

Gardeners and garden literature often use the word “blue” to describe the color of flowers that may be something different from blue. There is often a decidedly lavender or purplish tint to flowers we call blue. Admittedly, it can be disconcerting to see a flower that looks decidedly purple described as blue in a catalog. As a result, we often use the terms “true blue” or “sky blue” when describing really blue flowers.

You may see several wildflowers blooming along the roadside or in gardens in spring with blue flowers. Our native lyreleaf sage (Salvia lyrata) produces a low rosette of leaves, often colored with vivid purple, and an 8-inch-tall spike of lovely, light blue flowers.

During summer, a number of cultivated salvias produce true blue flowers in gardens — notably bog sage (Salvia uliginosa) and Argentine Skies salvia (Salvia guaranitica Argentine Skies).

Spiderwort (Tradescantia virginiana) is another native wildflower blooming in spring with triangular-shaped flowers in shades of blue to lavender-blue. Garden varieties are often hybrids with larger flowers and more robust growth, but the lovely wild forms you see in roadside ditches are also nice. They are well adapted to damp areas or average garden beds.

Finally, other blue wildflowers you may see blooming in the wild or in gardens this spring or early summer include stokesia (Stokesia laevis). This is a really great garden perennial for our area with lavender-blue, double-daisy flowers. Wild indigo (Baptisia australis) produces spikes of blue pea flowers. It is tough and durable in sunny areas and deserves much more use in Louisiana gardens. And blue-eyed grass (Sisyrinchium angustifolium) is one of my favorites.

Used in the cool-season vegetable garden as a salad green with a slightly bitter flavor, chicory (Cichorium intybus) is easy to grow in flower or vegetable gardens. What I love most about it, however, are not the edible leaves. I look for the masses of 1-inch, true-blue flowers produced in spring and early summer.

Several cool-season bedding plants produce blue flowers, including a number of pansy (Viola x wittrockiana) and viola (Viola cornuta) varieties that produce light to medium blue flowers with or without faces. It’s a little late to plant these now as they begin to fade out with summer heat. Plant these in October or November for months of flowers through winter and spring.

Columbine varieties (Aquilegia) are available that produce heavenly sky blue flowers. And delphiniums (Delphinium hybrids) produce tall spikes of flowers in shades of blue from pale sky blue to navy.

Delphiniums and columbines both may be available now in area nurseries. If you plant them this late in the season, choose large plants in gallon-size containers in or out of bloom. Small blooming plants may not produce the best results if they’re planted this late.

Annual lobelia is outstanding among the blue-flowered, spring-blooming, cool-season bedding plants. Low growing and forming a mound or mat that will drape attractively over the side of a container or raised bed, the plants literally cover themselves with flowers of various shades of blue from cobalt to sky blue. Planted now, flowering continues until it gets hot in June.

And I can’t neglect mentioning forget-me-nots (Myosotis sylvatica) for true blue flowers in mid- to late spring. Plant transplants of this cool-season bedding plant now or plant seeds in fall to late winter.

Wonderful perennials with blue flowers bloom in spring, including giant blue Louisiana iris (Iris giganticaerulea), ajuga Caitlin’s Giant (Ajuga repens Caitlin’s Giant), periwinkle (Vinca major) and blue star (Amsonia tabernaemontana).

During May, blue-flowered hydrangeas (Hydrangea macrophylla) are a delight. For blue hydrangeas, treat your soil with aluminum sulfate in March and October each year.

Agapanthus or lily-of-the-Nile (Agapanthus hybrids) produces large, round flower heads in a variety of shades of blue, from light sky blue to navy blue in early summer.

Blue daze (Evolvulus glomeratus) is an outstanding summer bedding plant. Plants grow to be 10- to 12-inches tall and a little wider. Nickel-sized, round flowers of sky blue are produced from spring planting to first frost.

And during the scorching heat of summer, nothing cools us down like the true blue flowers of plumbago (Plumbago auriculata). Its large clusters of light to medium blue flowers (Imperial Blue is a darker blue variety) and long blooming season make it among our very best blue flowers.

It takes some thought and effort to find and introduce beautiful blue flowers into your landscape plantings. But it is well worth the effort. Blues are easy to blend with other colors and go with virtually any color scheme. And nothing looks cooler on a hot summer day.

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