It is best to water your Rubber Tree every 1-2 weeks, allowing the soil to dry out between waterings. Opt for the more frequent end of the range when the plant is receiving more light, such as in spring or summer, and in the fall or winter, reduce the frequency.
For the young roots of Rubber Plant, apply a high phosphorus fertilizer to stimulate root development. As the plant matures to producing much foliage, apply a high nitrogen fertilizer every four (4) weeks during growth as this stimulates full and healthy foliage development.
The most likely reason the leaves of your Rubber Tree are fading from deep, dark, burgundy is due to a lack of light. Your plant prefers bright indirect light. It will tolerate low light, but the leaves will fade to a light green color.
Rubber plants prefer bright light but are adaptable to low light. They grow best with the morning light from an east window. They do well in warm to average room temperatures. The ideal temperatures are 60 to 65 °F at night and 75 to 80 °F during the day.
Repot the plants in late winter or early spring when the rubber tree is semi-dormant and less prone to transplant shock. Place 3 to 4 inches of potting soil in the bottom of the new pot. Water the soil in the old pot thoroughly, as moist soil helps with pot removal. Set the plant into the new pot.