I planted a Fragrant Sumac this past spring and was hoping to see the foliage turn scarlet but its the Santa Claus parade and the leaves are still green! We are mid-town and it gets full sun.
Leaves of the fragrant sumac (Rhus aromatica) generally turn orange, red and purple in the autumn. Although it is mid-November, be patient, as your shrub’s leaves generally change colour quite late in the season, well after most other deciduous plants have dropped their leaves.
Leaves contain 3 main pigments responsible for leaf colour: chlorophyll (green), carotene (orange-yellow) and anthocyanin (red-pink-purple). Although all 3 pigments are present in leaves, during spring and summer, chlorophyll predominates and leaves appear green. However, as the days get shorter and colder, chlorophyll production shuts down, leaving colours from the other 2 pigments visible in the foliage. It is believed that anthocyanin protects plants against excessive sunlight, so if the autumn is sunny, this red pigment will predominate. However, if the season is overcast, the leaves are more likely to turn orange-yellow in colour. As well, the soil pH (acidity/alkalinity) helps to determine the colour imparted by the anthocyanin (e.g., red and purple tones). For more details about how leaves change colour, see Science Daily. Why do leaves change color in the fall?
See also an earlier response to a similar question about a staghorn sumac at Toronto Master Gardeners. Sumac leaves changing colour in the fall. One suggestion was that a lack of red leaf colour may be because some sumac varieties may not produce as much of the anthocyanin pigment as others.
Although you cannot control how the weather/hours of daylight will affect your shrub’s leaf colour, it is important to make sure that you provide the plant with optimal growing conditions. It should thrive in full sun, in slightly acidic soil that is moist and well-drained. For good general information on care of shrubs, see Blooming Deciduous Trees and Shrubs: A Toronto Master Gardeners Guide.
All the best with your lovely sumac!