A Polish woman who grew marijuana to calm the nerves of her cow has been charged with cultivating a narcotic by police in the western town of Lobez.

The cow had been "skittish and unruly" -- once breaking a person's arm -- until someone suggested mixing cannabis in with its feed, the woman told police.

"The cow became as calm as a lamb," the 55-year-old woman said, according to the PAP news agency.

The woman's plants, grown from seeds she bought at a market, reached nearly three metres (yards) tall and were extremely potent, police said.

Marijuana possession is a crime throughout Poland. The woman faces up to three years in jail if convicted.