Probably best known as a large-leaf houseplant, the rubber tree (Ficus elastica) becomes a large tropical tree outdoors in frost-free areas of USDA Hardiness Zones 10 and warmer. The original source of rubber, its milky white sap is also sticky. Other names given to this species include Indian rubber tree and India-rubber fig.
Native to India, the native range of this fig tree species once extended from the southern slopes of the Himalayas south- and eastward all the way to Java and Malaysia. Today it is extinct in the wild, according to Margaret Barwick's "Tropical and Subtropical Trees" encyclopedic reference.
The gummy white latex found throughout all plant parts of the tree became rubber; this was the first tree species tapped for this use. Once exploration of the tropical New World ensued, the sap of the para rubber or hevea tree (Hevea brasiliensis) of Brazil superseded use of the Indian rubber tree.
Evergreen, this tropical tree matures to heights approaching 200 feet with massive, beige-barked trunks supported by aerial roots that reach downward from the lower sides of branches. Its leaves are stiff and leathery but beautifully glossy and emerald green, shaped like folded ovals with terminal pointed tips. In early summer, it bears small, greenish flowers of little ornamental interest, followed by rounded figs.
Outdoors, the rubber tree releases and grows quickly in hot, humid, moist soils in abundant sunshine, receiving six or more hours daily of direct sunlight. It tolerates shade in a forested environment as well as dry, compacted, occasionally flooding and alkaline soils. Indoors as a house plant, it grows robustly with as much direct sunlight as possible, but often sits and survives nicely in bright indirect light several feet away from windows. Allow the soil of interior plants to dry to the touch before watering, as over-watering remains a primary reason for the plant's death when grown in the cool, dry air and lower light levels in offices and homes.
While the emerald green foliage of the species remains an attractive ornamental feature, cultivated varieties have gained popularity, especially those with colorful leaves. 'Abidjan' and 'Burgundy' develop green-red to burgundy foliage if ample light abounds while 'Variegata' leaves look painted with creamy, pale yellow and light and medium green mottling. In sunlight, the leaves usually blush pink and all newly emerging leaves carry a rosy tone. 'Decora' and 'Robusta' are two selections with improved leaf shapes with deep green coloration.
The milky sap irritates skin and can cause itching and dermatitis in people with particularly sensitive skin. Avoid getting the sap into skin cuts and open wounds as well as eyes. Large trees develop strong surface roots that usually lift and break sidewalks and asphalt nearby, creating tripping hazards.