African milk trees are native to central Africa where they grow in the seasonally-dry, tropical biome of Angola, Congo, Gabon, Malawi, and Zaïre. This makes them well adapted to the dry, winter conditions suffered by most New York area houseplants.  They are somewhat difficult to grow indoors because they need generous amounts of daily sunlight. 

Water your plant to make all the potting mixture just moist with tepid water, then allow it to drain completely through the drain hole before removing the run-off water. The soil should nearly dry before you water it again. If the soil is allowed to stay too wet, it can kill the plant. Keeping your plant in a container that allows it to drain and then removing the water is essential to its health. 

Begin to taper the watering frequency in fall as days get shorter. Typically, in the low-light conditions of fall and winter (October through February), water only as often as is necessary to prevent your plant from slight wrinkling. Your plant is not in active growth at this time and prefers extended, nearly dry conditions. 

African milk trees do not need humidity to prosper, and misting is not advised. It is best suited to a dry to neutral environment with humidity below 50%.