Hair transplantation are not seasonal operations. It can be done each and every season. If you wish you can have it during the winter, or summer too... The things you need to be careful after your transplantation are closely linked with your social life.
For instance during summer months one has to avoid swimming and sun bathing for a week or so after their transplantation. UV rays can damage the cuts on the skin, however there is no risk for skins covered with hair. After hair transplantation, a patient should not wear tightly covering hats to protect themselves from cold during winter months.
The best time for hair transplantation is when you are not so busy, and when you can have time for yourself for 3-5 days. And, last but not least, after your transplantation, be it during the summer, or the winter, you really need to follow the advice given by your specialist.