Temperature and Bougainvillea Hardiness

Growth Cycle

• Bougainvilleas are woody vines that lack clasping tendrils. They clamber and hang on structures or other plants for support, with their branch thorns helping to lock the long branches into place. Bougainvilleas are perennial evergreens, with growth occurring in two cycles. One cycle is vegetative, when the plant mainly produces new stems and leafy growth without flowers. The second period is when all the new woody tissues produce buds and tiny flowers among the long-lasting bracts. Native to northern Brazil, growth and flowering cycles occur year round, never impeded by winter freezing temperatures. Heaviest flowering usually occurs in the short days of winter, but hot temperatures also induce prolific blooming.

Winter Hardiness

• Reliable survival of bougainvilleas occurs in U.S. Department of Agriculture plant hardiness zones 10b and warmer where the winter low temperature never drops below 35 degrees Fahrenheit. Bougainvilleas still grow in USDA zones 9b and 10a, but the threat of light frosts to moderate freezes at temperatures down to 25 degrees can occur. Plants may be killed if temperatures remain below freezing for more than four hours. Subfreezing temperatures less than that duration can kill back branches but the lower trunk and roots will survive, requiring new sprouts to grow in spring with the return of warmth.

Cold Damage

• When nipped by frost, bougainvillea vines usually drop all their papery bracts and lose most of their foliage. If the frost was brief, only bracts may drop and the leaves may reveal yellow and brown edges one or two days later. Plants that endured subfreezing temperatures for up to four hours likely sustain severe branch and twig desiccation, but the roots should survive. A bougainvillea will again grow as long as no additional frost or freezes occur to further harm branches or kill the root system.

Hardiness Insight

• In regions where light frosts often occur, bougainvilleas sustain the least amount of cold damage if planted next to a building that radiates heat off at night. Do not site plants in windy locales or low pockets where coldest air accumulates. Bougainvilleas grown in containers experience colder temperatures than those in the ground. Soil in containers readily cools to air temperatures and can more readily kill plant roots. Container-grown bougainvilleas may be killed by temperatures of 30 degrees for only an hour, especially if plants are stressed by dry soil. Tolerance to frost and duration of exposure to subfreezing temperatures varies among species and the numerous cultivars.