12 cm pot. Radermachera are not keen on change! Try and keep both temperature and watering regime as constant as possible. Grow in a well-draining medium to help prevent root rot.
Water well and regularly in the summer, but wait until the top inch of soil is dry before watering and don’t overwater – if the tips are going black then that is a sign of overwatering. They like hunditions so are suitable to grow in bathrooms.
Keep out of direct scorching light, semi-shade to bright windowsill.
It favours 18 -24 degrees C but can cope with a bit less.