Culture Report: Centaurea ‘Silver Swirl’
In a garden center and a world full of color, what is it that really stands out for consumers? What catches the browsing gardener’s eye that differentiates itself in the sea of choices? What makes a retail display draw the attention of the skeptical shopper?
The answer is silver.
Adding silver in a landscape design reflects the sunshine and glows in the moonlight. In a mixed container, the color silver can be used in every type of combination you could think of. As a standalone, it crafts a bright border or shines as an interesting specimen. In short, silver goes with everything!
To that end, Darwin Perennials has launched Centaurea ragusina ‘Silver Swirl’ as a stand-out addition to the silver foliage market. With its thick, rubbery textured leaves — I call it a “Hobby Lobby” plant — and bright silver-white foliage, which doesn’t green and seems to only get brighter in the summer heat and light, ‘Silver
Swirl’ is a unique addition for homeowners to choose for brightening their landscapes or patios.
‘Silver Swirl’ could also be used as an indoor pot crop. Darwin Perennials has completed some trials and found this variety holds up well for up to four weeks indoors. How do you suppose this would look grown in a 6-inch pot with a red sleeve as a Holiday crop? ‘Silver Swirl’ grows to about a 12-inch mound in northern climates where the growing season is shorter and can reach 18 to 20 inches in southern climates. One factor that contributes to this added growth is the heat. ‘Silver Swirl’ thrives in hot climates and is VERY drought tolerant once established.
‘Silver Swirl’ is a perennial for those in zone 6b and warmer. It will get attractive, buttonlike yellow flowers the following year. In colder climates, not only is ‘Silver Swirl’ frost tolerant, but it is also very freeze tolerant; it will not melt down even with repeated hard freezes.
Centaurea ‘Silver Swirl’ is propagated via vegetative cutting. Good general practices should be followed for rooting cuttings:
• Well drained media. pH 5.8-6.2, EC<0.80
• Media temperature 70-72° F/21-22° C. Bottom
• Rooting hormone IBA 500ppm dip or 250ppm
drip down spray
• 72-cell plug tray is ideal. Smaller cells are a
bit too crowded while larger cells can remain
• Pageant Intrinsic fungicide applied day 1 or 2
‘Silver Swirl’ is suitable for quart containers all the way up to 1.5 gallon. Finishing time will be directly related to temperature — the warmer the better. ‘Silver Swirl’ will not mind it HOT. However, temperatures below 62° F/16° C will increase the finish time.
In general, with a 68° F/20° C average daily temperature, I would expect 8 weeks to finish a quart, 12 weeks for gallons, and 14+ weeks for 1.5 gallon.
Transplant one plant per pot into a well-drained media. Again, do not allow the media to remain saturated for extended periods of time. Outdoor production in the South is ideal, but chances of flooding rains can be an issue. For indoor production in the North, provide the highest light and temperatures possible. In either region, no PGR will be needed.
Controlled release fertilizer at medium to high rate can be beneficial. Additionally, liquid feed may be applied as necessary. ‘Silver Swirl’ is not particularly salt sensitive but be aware of excessively high EC while growing the plants dry.
As far as issues go, I have never seen ‘Silver Swirl’ get so much as a leaf spot from overhead watering, but as mentioned before, excessively wet media can cause problems. Additionally, we have seen thrips on this like other centaurea.
Spring, summer, fall or holidays, ‘Silver Swirl’ can add a modern design touch to your customers’ landscape or container designs. Don’t pass this one up for your next perennial program! It’s a true stand-out for garden center and nursery sales.