Oxypetalum caeruleum – A Good Blue Tender Perennial

Oxypetalum caeruleum - A Good Blue Tender Perennial

December gardeningOxypetalum caeruleum is a South American member of the Milkweed Family which deserves to be better known. A reference to it in an English gardening magazine aroused my interest, and in the summer I sowed a packet of seeds in a flat. They germinated well, and in the autumn the little plants were potted up, and placed in the greenhouse for the winter. By April they were ten inches high and had begun to bloom. Set outdoors in May, in full sun, and in a. fairly rich sandy loam they flowered without a day’s interruption until the end of October when they were again potted and taken indoors. They have retained all their foliage, and now (arid-January) show signs of blooming again. I think it is probable that if encouraged to do so, they would flower eight or nine months out of the twelve.

The ultimate height of Oxypetalum – my garden, at least-is from a foot and a half to two feet. Although described as of trailing or twining habit, my plants have grown upright, with neat stiff stems that need no support. When broken, they exude the milky juice characteristic of the family, and the long pointed seed pods, filled with silken down, are also typical. The foliage is soft grayish-green and of velvety texture. The flowers are star-shaped, an inch or more across, growing in flat clusters over the top of the plant. They last for several days, even under the hottest sun, and are the only flowers I have ever seen which can be truthfully and accurately described as of the purest turquoise blue. This exquisite color is retained until just before the blossoms fade when they change to a pretty mauve.

Last summer the part of the border where my Oxypetalums were planted gave me particular pleasure, and since its charm was largely accidental arid owed little to any cleverness on my part, I may praise it without undue conceit. The edging was of Convolvulus mauritanicus and the low-growing Verbena bipinnatiflda: then came the Oxypetalum plants, with a generous mass of Aster frikarti nearby. In the rear, self-sown seedlings of Salvia France came up so fast that they were blooming by mid-June, and next to them was a large group of the decorative Verbena bonariensis, its tall slender wands crowned with helio-trope-like flowers. The silvery blue of the low-growing Verbena, Convolvulus, Aster, and Salvia, the turquoise of the Petaluma, and the soft reddish-purple of the tall Verbena made a delightfully cool and harmonious combination of color, which lasted in beauty from June until frost.

Oxypetalum caeruleum is not reliably hardy even in the British Isles but should be a good perennial for Southern gardens. Its exquisite color and neat growth, and its freedom of bloom over so long a season certainly make it highly desirable for the summer garden in northern latitudes, and it has been recommended also as a good winter pot-plant for the window or cool greenhouse.

by Antoinette Dwight
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