Sumac Leaves changing colour in the fall

(Question)

We live in the country, 25 kms south of Parry Sound (Zone 4B). We have a lovely “wall” of Staghorn Sumac on a slope near our home. The leaves do not turn red in the fall as I hoped they would. They stay mostly green and this year, some have turned orange. The fruit is abundant and red. Why do our sumac not turn red in the fall?

(Answer)

Dear gardener, your question puzzles me too.

Biologically, leaves change colour due to several factors, namely: light, temperature and pH.

Light: sunny days are needed in the fall for the brightest colours, particularly orange and reds. Overcast fall days usually lead to more yellows and browns. Also, as the levels of light diminish in the fall, plants start reducing their production of chlorophyll (responsible for the green colour) in preparation for their dormant period. As chlorophyll decreases, other pigments already present in the leaves become more obvious: pigments such as Carotenoids (responsible for the light yellow colour) and  Tannins (responsible for yellow and brown colours). Anthocyanins (responsible for the red colour) appears as the sugar levels increase in the fall. Plants that contain sufficient amounts of Anthocyanins and carotenoids pigments, will turn orange; plants with sufficient levels of Carotenoids and Tannins will torn golden yellow, etc.

Temperature:  as the evening temperature starts to drop, there are chemical reactions in the leaf pigments that will affect their fall colour. Warm sunny fall days and cool (not freezing) nights, produce the best colours as the leave veins contract and the sugars produced during the day remain on the leaves instead of being transported back to the roots. Early frosts do not allow the proper mixture of sugars and pigments.

pH: Staghorn Sumacs (Rhus typhina spp) prefers slightly acidic soils. Cells pH influences the red colour of Anthocyanins which is usually produced in the fall.

Sadly, this information does not completely explain why yours are not changing. Take a look at the amount of light the bed receives as that could be an indication. Also, some varieties may produce more or less of the particular pigments which may be another reason for the lack of colour. The good news is that the plants are obviously thriving and giving you and abundance of fruit which would look lovely against the white snow of the winter!

Thank you for contacting us.