Gardeners prize the Viburnum trilobum--also known as the American cranberry for its bright crimson fruit--for ornamental purposes. It's one of the best ornamental viburnum shrubs, according to Ohio State University, and produces a profusion of red fruit and white flowers against glossy green foliage. Soil amendments and conditioners, and the rare application of shrub fertilizer, help keep your viburnum shrub growing vigorously.
Amend the soil with 2 to 3 inches of aged compost. Viburnum trilobum shrubs thrive in moist, well-drained soil, according to North Carolina State University. Aged compost adds micronutrients to the soil to feed viburnum roots, improves the soil's ability to retain moisture and enhances drainage.
Test the soil's pH levels. Viburnum shrubs grow best in neutral soils with a pH of 7.0, according to the University of Rhode Island. At different pH levels, the plant can't absorb all the nutrients present in the soil. Many garden stores sell soil test kits. If needed, the pH can be raised using agricultural lime or lowered using ammonium nitrate. The amount needed to amend the soil varies according to the soil's current pH levels. Your local cooperative extension office can offer region-specific guidance.
Fertilize the viburnum shrub. The shrubs rarely need fertilization due to their hardy nature, according to North Dakota State University. If you choose to fertilize, the university recommends applying 1 cup of 5-10-5 fertilizer per viburnum shrub. For best results, fertilize in the spring when the plant enters its growing phase.
Apply water after fertilization to moisten the soil to a depth of 5 to 6 inches. This helps carry the fertilizer down to the shrub's root level for immediate feeding.