My indoor banana plant seems to be growing another sprout on its side. Should I cut this off or let it grow and cut down the original tree?
Yes, it actually is a good idea to separate the sucker from the mother plant.
The baby plant compete with the mother.
To ensure that the sucker plant is viable to grow on it's own, it should be at least 3 feet tall and 2 to 6 inches in diameter.
Tip the plant and pots on it's side and gently slide the roots and soil from the pot.
Brush away any soil from the sucker to expose the sucker. Using a clean and sharp knife remove the sucker from the mother plant roots.
Plant the sucker in a pot that is adequate sized; it will need to be a the same depth it was previously.
Use a good quality and well draining potting soil. Water the plant well.
Return the mother plant to her pot and add additional soil.