Plants that thrive during Oklahoma summers: Madagascar periwinkles

June 24, 11:10 AMOklahoma Gardening ExaminerDee Nash

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Because the temperatures in Oklahoma gardens have topped one hundred degrees for several days in a row, gardeners have asked which plants do best in the heat?  A summer series profiling those plants with the most heat resistance debuts this week.  With water, most established plants will survive hot summer temperatures, but for those that thrive, consider the following:

Where part of the world did the plants or its ancestors call home?  Mexico, South America, the tropics?

Madagascar periwinkles (Catharanthus roseus) love the hot sun and hail from Madagascar on the southeastern coast of Aftrica.  Catharanthus roseus may also be listed in some literature as Vinca rosea, Ammocallis rosea, and Lochnera rosea because it was formerly classified as such. 

Other common names include rose periwinkle and cape periwinkle.  It is not a true periwinkle, but is instead related to the dogbane family.  Madagascar periwinkles are hardy to zones 9 - 11 where they grow into a semi-shrubby perennial.   In Oklahoma, they remain a small but mighty annual which impacts the landscape with cheery nonstop color.  They outperform many other annuals in hanging baskets and as a small edging plant for the herbaceous bed or border.

• Grows six to eighteen inches.
• Should be spaced eight to ten inches apart for best growth.
• Grown in sun to partial shade.  It can take the hot summer sun with aplomb.
• Loves poor, well-drained soil.  Soil that is too rich inhibits flowering.
• Can be grown from seed or from root cuttings.
• Susceptible to Fusarium wilt and blight.  However, waiting to plant until hot weather has arrived and spacing the plants far enough apart both help with these diseases.

Non only is Madagascar periwinkle used as an ornamental plant, it has also been used as an herbal remedy for diseases like asthma, high blood pressure, diabetes and certain types of cancer.  However, not that it is poisonous to smoke or ingest Catharanthus roseus, and it is poisonous to grazing animals.