Sweet William is an aptly named, fragrant plant that performs in most climates as a biennial plant. Since it usually lasts only two seasons, preparing the plant properly for winter can help extend its life. In some climates, sweet William behaves as a perennial, offering compact red, white and pink blooms year after year. If you have this kind of luck, winterizing the plant to keep it healthy year after year. Gardeners in moderate zones may actually see very little leaf shedding during cooler months. Sweet Williams are part of the dianthus family of flowers that complement any garden with color, little mounds of greenery and abundant flowers.
Clip off dead blooms behind the flower bud during the growing season. This encourages the plant to continue blooming without expending energy on seeding.
Control plant growth and prepare for winterization by clipping back the sweet William right after it has finished blooming during the growing season. Remove any overgrown or spindly stems and continue watering throughout the summer, despite the lack of blooms.
Do not clip the plant in the fall. Allow the leaves and stems to die naturally from exposure to the cold. Do remove any portion of the plant that shows disease, such as spots or mildew. Let the plant's dead growth fall to the ground. The decomposing leaves and stems will serve as organic matter than can enrich the soil.
Apply a 6-inch layer of very loose, shredded mulch to the ground above the sweet William after all foliage withers and dies. This mulch layer will insulate the plant during the coldest months. Don't pack the mulch tightly but instead, place it loosely above and around the plant directly on top of the dead foliage. The mulch will retain moisture and keep the ground at an even temperature.