Diamonds Blue delphiniums sparkle in the cool-season garden

Richard Bogren, Gill, Daniel J.

For Release On Or After 10/25/13

By Dan Gill
LSU AgCenter Horticulturist

An exceptional, blue-flowered, cool-season bedding plant called Diamonds Blue delphinium (Delphinium chinensis Diamonds Blue) is a Louisiana Super Plants selection for fall 2013.

The Louisiana Super Plants program is an LSU AgCenter educational and marketing effort that highlights tough and beautiful plants that perform well in Louisiana landscapes. Louisiana Super Plants selections have a history of outstanding performance in Louisiana or have gone through several years of university evaluations and observations. Louisiana Super Plants are “university tested and industry approved.”

The Louisiana Super Plants program has three parts. The first identifies outstanding plants, which is done by LSU AgCenter horticulturists with input from representatives of the Louisiana green industry. The second gets the word out to Louisiana gardeners.

And that brings up the third part – the Louisiana Super Plants program works closely with wholesale growers in Louisiana to ensure they produce plenty of the selected plants. Retail plant sellers are kept informed of the selections and are encouraged to carry them. For more information, go online to Click on “Where to Find Super Plants” to find participating retail nurseries near you.

Blue and beautiful

True blue flowers are relatively rare in nature and, as a result, not so common in our gardens. When gardeners use the word “blue” to describe the color of flowers, we sometimes fudge a bit. There is frequently a decidedly lavender or purplish tint to flowers we call blue. As a result, we often use the terms “true blue” or “sky blue” or “really blue” when describing flowers that are actually blue.

If you love blue flowers, Diamonds Blue delphinium is really, truly blue – an intense, vivid, almost electric blue that sings out loud and clear in the flower garden. Blue flowers are so useful in the garden. They combine well with and complement virtually any other color, from cool pinks, lavenders, purples and burgundy, to vibrant yellows, golds, oranges and reds.

If you have seen pictures of blooming delphiniums in gardening books or magazines or on TV, you likely think of these as tall-growing plants reaching 5 feet tall with large, upright spikes of flowers. Diamonds Blue is a completely different plant altogether. This is because it is a different species from those tall, stately hybrid types.

Diamonds Blue is a variety of Delphinium chinensis, a species that is bushier and lower-growing. These plants are only about 14 to 16 inches tall and about 12 to 14 inches wide. This compact growth habit makes them ideal for containers and cool-season flower beds when they’re planted to the front or middle of the bed.

The uniquely beautiful flowers and compact growth habit are not the only reasons Diamonds Blue was named a Louisiana Super Plants selection. In variety trials at the LSU AgCenter Hammond Research Station, Diamonds Blue showed more vigor and stamina over a longer period than other delphiniums. This variety produces more flowers over a longer blooming season as well. And it has no major insect or disease problems.

The foliage of Diamonds Blue delphinium provides a beautiful background to the flowers. Rich green and finely divided, the texture is delicate. But don’t let that fool you. These plants are tough and resilient and hardy through the freezes of winter.

Cool-season bedding plants are generally best planted in fall and grown through mid- to late spring when the weather begins to heat up – about October/November through April/May. Ideally planted in the fall, Diamonds Blue delphiniums can be planted as late as February and produce outstanding results. But the fall planting is best.

Plant these now, and you’ll enjoy flowers in the garden from fall or early winter to spring. This gives you more bang for your buck. In addition, the spring display is superior with fall planting because these bedding plants keep growing through the cool winter season. By spring, the plants are large and robust with well-developed root systems – which lead to a spectacular floral display. This is basically true for all of our cool-season bedding plants.

When you plant, do a good job of bed preparation, which makes a tremendous difference in the plants’ performance. Remove any weeds in the bed and turn the soil to a depth of at least 8 inches. Spread a 2- to 4-inch layer of organic matter (compost, peat moss or aged manure), evenly sprinkle a light application of a general-purpose or organic fertilizer over the bed and thoroughly mix it all into the soil. Rake the bed smooth, and you’re ready to plant.

Plant transplants about 12 inches apart at the same depth they were growing in the container. After planting, apply an inch or two of mulch, and water the plants in thoroughly.

The compact, bushy growth habit makes this plant extremely versatile and useful in the landscape. It combines beautifully with a wide variety of other cool-season bedding plants in mixed planting containers. Try pairing it with Amazon Rose Magic dianthus, dusty miller and white alyssum. In flower beds, it should be planted toward the front of the bed, but it could be planted behind very low-growing cool-season bedding plants like alyssum, viola and lobelia.

Wherever you plant them, Diamonds Blue delphiniums shine with the brilliance of intense blue diamonds over a long blooming season. Their vigor and stamina make them a super choice for your cool-season gardens.

Rick Bogren

9/30/2013 8:11:56 PM
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