couple of years old and is growing inside.

==>>. inside what ...

whats the ambient humidity ...

where are you.. furnace.. or a/c ...

as its gotten colder.. has your furnace kicked on yet ...

how about a pic of the whole..

other than in side.. and number of hours of light.. you havent told us much of anything ...

ken

It is inside my garage in a hydroponics grow tent. The insides of the tent are reflective so that the plants get maximal light all around. Relative humidity is 55% to 60% MC. The container in which the small tree is planted is a half-gallon container with drain holes. I've also stated the temperature, i.e., 70F. The soil is Miracle-Grow Potting Mix, and for the past 6 months, the tree was growing very rapidly and had normal leaf color.

Pull it out and check the root system. Bagged potting mixes tend to be too high in organics, leading to water retention and rot. You can normally cut them by half with vermiculite or some other inorganic and have a much happier root system.

Look for Al's 5-1-1 mix in the container forum. It would greatly cut down risk of root rot and trees will thrive in that mix.