Can seasonal variations cause asthma?

Hello doctor,

My mother was diagnosed with asthma nine years ago and used inhalers that the doctor prescribed. The doctors suggested that it might be due to climatic conditions, as she got an asthma attack during winters. This same pattern of asthma attacks repeated for the next five years. My mother had no episodes of asthma attacks for the next four years. We shifted to a new place one month ago, and my mother again had an asthma attack. Many flower-bearing plants surround our new house, and when we consulted the doctor, he said that she might be allergic to pollen which had triggered the attack. Is it possible that the initial and the recent attack is due to different reasons? Has my mother been allergic to pollens the entire time?