Bought a Agapanthus late October, it's roots were tightly wrapped around itself that pot had to be cut. I could not separate the roots to help them spread out. It's repotted in a bigger container with potting soil, with a west facing window nearby. The leaves are yellowing, it is watered about once a week. What can I do to stop the yellowing of leaves? Is it going through a dormant phase? Any information you can provide will be greatly appreciated. Thank you.
Yellowing leaves are often caused by overwatering in container plants. Larger pots hold onto more water than smaller pots, so your plant will probably need to be watered less frequently than when it was in its smaller pot. Push your finger into the soil each time before you water to make sure the soil isn't staying too damp.
Higher light levels could also help your plant green up. A disease is unlikely, but check this article just in case: