The rubber tree plant (Ficus elastica) is typically grown as a houseplant but can be grown outdoors in U.S. Department of Agriculture plant hardiness zone 10 through 12. Like its cousins weeping fig (Ficus benjimina) and fiddle leaf (Ficus lyrata), both tropical figs, it craves plenty of humidity and consistently moist soil.
Rubber Tree Facts
Fig species are natives of the rainforests stretching from the Eastern Himalayas through Assam and Burma, down the Malay peninsula to Java. Several of its relatives, including fiddle leaf fig, grow as vines in the forest understory, climbing trees, but the rubber tree rises from strong roots on the forest floor, sometimes as high as 50 to 100 feet in its native habitat. The extremely porous soil of the rainforest results from layer upon layer of leaves and other plant material leached through by high humidity and frequent precipitation. Rubber tree grows easily in semi-tropical climates in southern Florida, but needs extra water in Southwestern desert and West Coast Mediterranean-type climates.
Garden Rubber Trees
Rubber trees seldom reach more than 20 to 40 feet tall in home gardens -- and then only with careful siting and pruning. The soft-wooded trees need shelter from strong winds and strong afternoon sun, but tolerate full morning sun in all but the hottest weather. Rainfall in tropical rainforests might be 50 to 260 inches with rainy and dry seasons. Temperatures normally range between 68 degrees and 94 degrees Fahrenheit and humidity values fall between 77 and 88 percent. The deficit between your local climate and rainforest averages helps determine how much extra water, if any, your rubber tree requires beyond natural precipitation.
Few backyards have the same soil of the rainforest -- humus-rich soil, filled with bacteria and fungi, energetically eating nutrients. Rainforest soil has evolved over millennia and drains faster than garden soils. So even in tropical climates, the shallow roots need enough -- and just enough -- water to keep the soil moist, never wet. Rubber trees do, however, tolerate some drying. In South Florida, your rubber tree plant may need little additional water if rainfall averages 100 inches on sandy soil, but in Southern California, you may need to water to achieve at least 1 inch of water to keep your plant’s soil moist.
Rubber tree’s large, smooth leaves transpire large amounts of water-- not a problem when humidity averages 82 percent. Where humidity falls to 40 or 50 percent or temperatures rise above 115 degrees Fahrenheit, though, plants need extra water. Container plants -- even those with humus-rich potting mixes -- are more susceptible to heat. Check soil in containers daily for drying; water when the top inch becomes dry. Water all rubber trees with a soaker hose or drip irrigation to keep water off foliage -- overhead watering encourages development of anthracnose, Corynespora leaf spot and scales.