Cupressocyparis leylandii 'Castlewellan', commonly known as Castlewellan Gold, is a striking evergreen conifer widely appreciated for its vibrant, golden-yellow foliage and fast-growing nature. This cultivar forms a dense, pyramidal shape, making it excellent for privacy screens, windbreaks, or as a standout specimen in the landscape. Its foliage retains its bright golden hue throughout the year, providing year-round interest and contrast against darker greens. 'Castlewellan' tolerates pruning well, allowing gardeners to shape it to fit their desired landscape needs.

- Light: Full sun to partial shade
- Water need: Moderate; ensure well-drained soil
- Growth rate: Fast
- Mature size (HxW): 40–60 ft x 15–25 ft
- Habit: Upright, pyramidal, compact form
- Bloom/interest: Evergreen, golden foliage year-round
- Hardiness zone: 6–9
- Soil tolerance: Adaptable; prefers well-drained soils
- Drought/heat tolerance: Moderate once established