My rubber tree is growing too tall. It is the variegated leaf type. The main stem has no branches, just a pair of leaves about every 6 inches up the stem. It is in good condition, intact with all its leaves. I would like to propagate it by cutting about 3 feet off the top. Is air layering good for this project? And how should it be done? Also, I will be left with 3 feet of the original plant. Will this continue to grow or should it be discarded? I would be grateful to hear your views on this subject.