This could be The Day of the Triffids:
The Day of the Triffids is a 1962 British film based on the 1951 science fiction novel of the same name by John Wyndham. The picture was directed by Steve Sekely, and Howard Keel played the central character, Bill Masen. The movie's leading lady was Nicole Maurey (who played Christine Durant), and it was filmed in color with monaural sound.
Triffids are tall, carnivorous, mobile plants capable of aggressive and seemingly intelligent behaviour. They are able to move about by "walking" on their roots, appear to communicate with each other, and possess a deadly whip-like poisonous sting that enables them to kill their victims and feed on their rotting carcasses.
Bill Masen (Howard Keel), a merchant navy officer, is lying in a hospital bed with his eyes bandaged. He discovers that while he has been waiting for his accident-damaged eyes to heal (the accident that caused Masen to be blinded is never explained), an unusual meteor shower the night before has blinded most people on Earth. Once he leaves the hospital, Masen finds people all over London struggling to stay alive in the face of their new affliction. Some survive by cooperating while others simply fight, but it is apparent that after just a few days society is collapsing.
Masen rescues a school girl named Susan (Janina Faye), who has no parents and is a ward of the state, from a crashed train, and they decide to leave London and head for France. Masen and Susan find refuge at a chateau, but when it is attacked by escaped sighted convicts, they are again forced to escape; shortly afterwards, the Triffids attack and kill everyone in the chateau. The Triffid population continues to grow, feeding on people and animals. Meanwhile, at a lighthouse on a coastal island off Cornwall, Tom Goodwin (Kieron Moore), a flawed but gifted scientist, and his wife Karen (Janette Scott), battle the plants as he searches for a way to conquer them. Goodwin eventually finds the answer, which has been right there all along: salt water.