I purchased this dwarf orange tree online, and it has lasted for about a year now. However, it's leaves have started to fall, despite looking green and healthy. I keep it inside next to a grow light, and water it about once a week. I've even started misting it daily, since the air is so dry. What can I do so whip this tree back in shape? I feel like I've kept it on life support for the past few months. How can I get it to grow?