Electric blue flowers of Diamonds Blue delphinium are unique in the cool-season landscape. (Photo by Allen Owings)

A superior selection of taller-growing, cut-flower-type delphinium is the Guardian series. (Photo by Allen Owings)

Diamonds Blue delphinium still look good in late April in the plant trial gardens at the LSU AgCenter Hammond Research Station. (Photo by Allen Owings)

News Release Distributed 10/25/13

By Allen Owings
LSU AgCenter horticulturist

HAMMOND, La. – Many home gardeners know the tall, cut-flower-type delphiniums. These are excellent plants for the cool-season landscape in Louisiana.

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

The relatively new Diamonds Blue is a variety of Delphinium chinensis, a species that is bushier and lower-growing than our traditional, taller-growing varieties. Diamonds Blue is seed propagated. 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 planted to the front or middle of the bed. Plant them in full sun.

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. And this variety produces more flowers over a longer blooming season as well. In addition, it has no major insect or disease problems.

The foliage of Diamonds Blue delphinium provides a beautiful background for 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 winter freezes. The plant generally is considered a first-year-flowering perennial, but it should be treated as a cool-season annual in Louisiana.

Although not a Louisiana Super Plant, the Guardian series delphiniums has also performed well in LSU AgCenter trials. These are the type delphinium that most home gardeners are familiar with. Tall plants with 24-inch flower plumes, Guardian delphiniums feature flower colors of white, lavender and blue.

It is best to plant Diamonds Blue delphinium in fall (mid-October through November), but you can also plant in mid- to late winter (January through early March). When they’re planted early, they sometimes will begin blooming in the fall.

Plants need to be dead-headed to keep blooms going through winter and into early and midspring. In landscape trials at the Hammond Research Station, Diamonds Blue delphinium has typically been planted in October or November and has lasted until early June of the following year. Plants really are at their best in the landscape from March to May.

To enjoy Diamonds Blue delphinium through spring, you have to consider landscape bed preparation, fertilization, soil pH, irrigation practices and more. Properly prepare the landscape bed to allow for good internal drainage and aeration. If you purchase soil, make sure it comes from a reputable supplier. Cheap soil often is not worth the price you pay. Make sure landscape beds have a soil pH between 6.0-6.5.

You can add fresh, nutrient-rich, finished compost to landscape beds to provide nutrients. Compost also is a great source of organic matter. For a traditional fertilizer approach, apply a slow-release fertilizer at planting. Most slow-release fertilizers for home use are three- to four-month formulations.

Diamonds Blue delphinium joins the Drift series of smaller-growing ground cover-type landscape shrub roses as a Louisiana Super Plant selection this fall. An additional Louisiana Super Plant variety will be announced in mid-November. You can see more on Louisiana Super Plants here.

You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.

Rick Bogren