Whether it terracota plant pots in the garden or greenhouse - or more decorative pots for house plants, its always a good idea to give them a though clean inside before reusing.
Normal brushes don't handle the shape of the inside of a pot particularly well.
This conical brush from Redecker in Germany has been specifically designed for that job. Made using Bassine fibres which are stiff enough to clear soil easily. Diameter at the tip is 8 cm, sloping to 12 cm. The handle is made from oiled Beech. Overall length is 25 cm.