The artist used a methodical approach to his compositions. He often chose a low perspective to emphasise the rows of tulips and hyacinths. This technique created a sense of depth without relying on dramatic central subjects. His work shifted from the dark tones of early Dutch realism toward a brighter palette influenced by Impressionism. In pieces like Achterzijde van Paleis Huis ten Bosch in Den Haag, he balanced the formal lines of architecture with the soft textures of the surrounding gardens.

Modern collectors value Koster for his ability to combine botanical precision with atmospheric effects. His paintings provide a window into the historic Dutch countryside before urban expansion. The repetitive patterns of the flower beds offer a rhythmic quality that suits contemporary interior design. His prints bring a calm, organised beauty to a room. They represent a specific moment in art history where traditional subjects met a new interest in light and air.