Which type of flowers are typically used to fill in an arrangement and have large rounded heads?

Mass flowers are characterized by their ability to fill space within a floral arrangement due to their large, rounded heads. These flowers are designed to create volume and provide a fuller appearance, complementing the overall design by adding richness and texture. Common examples of mass flowers include hydrangeas, peonies, and dahlias, which have a dense, lush form that serves to enhance the visual impact of an arrangement.

In contrast, form flowers, while also important in floral design, are typically used to create focal points through their unique shapes and structures. Line flowers are recognized for their height and linear qualities, often used to add movement and structure to an arrangement rather than fill space. Secondary flowers generally refer to those that provide accents or additional visual interest but do not primarily serve the role of filling an arrangement like mass flowers do.