Brown Buds On Arborvitae . Last fall i planted a row of green giant arborvitae. Soil that is moist, rich and deep, but well drained; My Arborvitae have developed these black leaves, anyone know the cause from www.reddit.com To determine if a browning evergreen will produce new growth, check the buds at the tips of the branches. Arborvitae > foliage > foliage turns brown from tip of twig down. Even then, consider if adequate water is.