WASHINGTON — On Monday, Bao Bao, the National Zoo’s panda cub, will be 18 months old.

“It’s hard to believe,” zoo officials said. It’s when they stop nursing and start living apart from their mothers.

The relationship does not change overnight. In what the zoo said is the normal course of panda development, Bao Bao began the weaning process a few months ago.

By now, it is noticeable. The amount of bamboo and solid food in the cub’s diet has increased significantly, the zoo said. Bao Bao now dines apart from her mother, Mei Xiang, and has spent about six hours a day separated from her.

Ultimately, the zoo said, time spent apart will increase until the cub, born Aug. 23, 2013, begins to live on her own. The zoo expects the process to be over by early March.

The zoo said she has also shown herself as something of a snow lover.