The 'Climax' plum is a hybrid variety that belongs to the genus Prunus, which is part of the Rosaceae or rose family. Prunus includes plums and damsons, edible fruits that usually have a glabrous or grayish bloom on the skin. 'Climax' is a round variety, similar to those sold in grocery stores. Though it was the product of crosses between Asian plum varieties, it was bred in the United States over a century ago.
Parents: Prunus Simonii
One of the parents of 'climax' was the Simon or apricot plum (Prunus simonii), which is native to China. Prunus simonii was introduced in the United States in about 1881 and was widely disseminated, but mostly grown in California. The fruit was yellow and the skin a dull red. In his "Hortus Third," Liberty Hyde Bailey noted that while Prunus simonii arrived in the United States from China, it was not known in the wild there.
Parents: Prunus Salicinia (Triflora)
The other parent of 'climax' was the Japanese plum, Prunus salicinia, sometimes known as Prunus triflora for its three-flowered clusters of spring blooms. The pointed fruit of this species is yellow or light red. Bailey notes that though Prunus salicinia was cultivated in Japan for its fruit, it is native to China. Prunus salicinia is somewhat less cold tolerant than Prunus simonii. The former is hardy to USDA Zone 8, while the latter can survive temperatures in USDA Zone 6.
Plums: Burbank Work
The 'climax' plum was one of over 100 plum and prune varieties developed by California horticultural pioneer Luther Burbank (1849 to 1926), who introduced 'climax' in 1898 or 1899. Other new plum hybrids released during the same two-year period include: 'Apple,' 'America,' 'Chalco,' 'Pearl,' 'Sultan,' 'Bartlett' and 'Shiro.' While working on the new plum hybrids, Burbank also perfected new varieties of quince, blackberry, blackberry-raspberry hybrids and tomatoes. Some of Burbank's original fruit varieties are on display at his home and garden in Santa Rosa, California.
Japanese Hybrid Plums Today
'Climax' plum trees are no longer offered in mainstream nursery catalogs. Other Japanese hybrid plums are still important, however, and constitute the majority of plums sold in supermarkets.Those wanting to grow Burbank's Japanese hybrid trees can still purchase his 'Burbank,' 'Santa Rosa' and 'Wickson' varieties from specialty nurseries in the United States.
Plum trees purchased bare-root (not potted) should be planted in raised beds or berms, since the plants do not thrive without good drainage. 'Santa Rosa,' a variety like 'climax' is self-pollinating, so while planting more than one specimen is desirable, it is not necessary. Plum trees bloom in spring and the fruit ripens from midsummer through fall, depending on the variety and weather. The genus is susceptible to a variety of pests and diseases, which can be controlled by organic means or through selective application of chemical controllers. Local cooperative extension agents can provide further information on the specifics of plum culture.