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Newsletter: Rabdosia longituba
Plectranthus is another name for this as yet unknown collector’s perennial that is slowly working its way into catalogs and gardener’s favorite lists.
Airy is the one word best used to describe Rabdosia. From a woody crown tall stems reach four feet, or more, in height with opposite foliage up the stems. Each serrated leaf is about 5 inches in length by 1 ½ inches across with a long petiole. Where the petiole joins the stem is usually a second set of smaller leaves on long petioles of their own. Each stem and secondary offset will have panicles of blooms at the tips.
Pale sky-blue blooms are on open panicles that reach up to a foot above the stems. Each tiny bloom is tubular in shape reaching only an inch or so, but with the numerous panicles the plant looks as though the sky decided to descend and hover about the green foliage.
I have my plants on the west side of my garden in decent woodland soil within the afternoon shadows of trees. My plants receive plenty of light, but little direct sun and seem to be happy in this location. The plants seem to respond to drought rather well, staying nice and green until I can get back out with a sprinkler to revive the garden in late summer.
Rabdosia does not break dormancy until late spring, so some patience is needed for Rabdosia to take its place in the garden each year. I would encourage cutting back the stems in mid-July to force shorter stems and more branches for less flopping about and more blooms in tighter panicles.
It does not bloom until late autumn, which is early October for me, so if you have an early frost, the blooms and foliage will be damaged. The plant is very sensitive to frost, so even a light one will turn the foliage black. Still, it is a well worth the space I give it in my garden for it brings delicate color at a time when color is desperately needed. Hardiness is rated for Zone 6 in winter.
For companions I have fall blooming anemone across the path from my Rabdosia. A limestone sculpture is the center piece within a curve in the path, and at its base are my blue beauties of Rabdosia, the golden flow of ‘Al Gold’ Japanese shade grass and Japanese blood grass with its burnt-red tips.