The reason that the Book of Ruth is read during Shavuot is not only because it occurred during the harvest season, but because it signifies our acceptance of the Torah.
During Shavuot, young children traditionally begin Hebrew School at Shavuot, and synagogues are decorated with greenery. Milk and dairy products, such as cheese, are usually taken this day, to symbolize the richness of the Torah.
We may also decorate our synagogues and homes with roses or aromatic spices. This custom is based on midrashim that connect the events at Sinai to spices and roses.