Plant of the month: Cotinus coggygria

There are several plants displaying their rich autumnal glow at Crathes Castle this month, including Cotinus coggygria Rubrifolius Group and Cotinus coggygria ‘Royal Purple’. These plants can be found in the Red and Upper Pool gardens, stubbornly holding their leaves in defiance of winter.

Cotinus coggygria (also known as Rhus cotinus) is a deciduous shrub or small tree, with rounded leaves. It originates from a wide-ranging area stretching across southern Europe all the way to Asia. Cotinus coggygria is in the Anacardiaceae family, commonly known as the cashew or sumac family, as reflected in some of its popular names such as Venetian sumach and Turkish sumac. Another common name is dyer’s sumach because a yellow dye (called young fustic) can be extracted from the wood of Cotinus coggygria – this was highly valued in the Middle Ages.

Today, it is predominantly grown for its show-stopping fiery autumn colours and the feathery, billowing clouds of its high summer flowers. These paniculate (growing in clusters along a branch) flower heads are loose and open, with many branching stems. The small inflorescences produce a relatively sparse amount of seed, with the non-flowering terminals becoming hairy as the season progresses. These contribute to the visual ‘smoky’ effect and are the reason Cotinus coggygria is referred to as the smoke bush.

The purple-leaved cultivars of Cotinus coggygria have become the most popularly grown, with the best leaf colour produced in full sun or partial shade. They can be hard pruned in late winter to encourage larger leaf sizes, providing stunning arched branches of yellows, oranges, rich reds and deep purples the following autumn. The intense and diverse colours and patterns produced by carotenoids (natural pigments), such as xanthophyll (yellows) and beta-carotene (oranges), remain longer in the leaf and become more prominent as the chlorophyll recedes. Another pigment contributing to the colours is anthocyanin (deep reds and purples). This is created by excess sugars becoming trapped within the leaf as they naturally detach and fall from the branch.