Casual Gardener: Plants reverting to type is bad sport

You need to be vigilant to retain those qualities that came from a mutation

The variegated green and yellow leaves of Euonymus fortunei
The variegated green and yellow leaves of Euonymus fortunei

The plants in our gardens take many forms and differ in how they have developed, whether it’s over millennia or merely decades. Some very familiar plants, such as foxgloves and teasel, are native species that grow from seed and will flourish regardless of any encouragement from humankind. Others are created by breeders, who will deliberately hybridise two plants and produce an entirely new cultivated variety, or cultivar.

Then there are the mutations, those very individual plants, or even parts of plants, which by some fluke of nature develop differently. Botanists call these genetic mutations sports and they can differ in shape, foliage, fruit, structure or colour.

Very often the characteristics of the sport, such as a variegated leaf or twisting branch, are regarded as desirable and therefore propagated, again producing a new cultivar, which will likely be sterile and can only be reproduced by taking cuttings.

Corylus avellana Contorta 'Red Majestic' –the corkscrew hazel. Picture by John Manley
Corylus avellana Contorta 'Red Majestic' - the corkscrew hazel

One of the best known examples of a sport is x Cupressocyparis leylandii ‘Castlewellan Gold’. Millions of trees worldwide are the progeny of a single tree, not seen before or since, that grew in the arboretum in what is now Castlewellan Forest Park in Co Down. It was produced by an accident of nature in 1962 when seed from cones of Cupressus macrocarpa Lutea standing next to a Chamaecyparis nootkatensis Lutea were sown by the then head gardener, John Keown. It seems hybrids between these the two species aren’t that unusual but the golden yellow foliage is.

Bud sports are mutations on a single branch, of which the nectarine is one, developing from a peach. Ruby red grapefruit and blood oranges are examples of citrus fruit mutations.

Providing quirky interest, sports are a often a good focal and talking point in the garden. Two of my favourites are the variegated Phormium ‘Yellow Wave’ (New Zealand flax) and the purple-leaved corkscrew hazel, Corylus avellana contorta ‘Red Majestic’, which has possibly mutated twice – first twisting its branches, secondly transforming the foliage from green to deep claret.

However, for all their allure, they are not without their drawbacks.

Plants derived from a sport are propagated by joining a cutting from the ‘unique’ plant to the roots of a related plant, fusing the two together in a skilled process called grafting. This marriage combines the qualities of the plant’s upper section, or scion, with the vigour and/or resilience of the the so-called rootstock.

It’s this vigour and resilience that cause the problems. In a process known as ‘reversion’, the rootstock sends up more vigorous growth that has reverted to type and, if not unchecked, grows much quicker than the weaker cultivar. With the phormium, for example, thicker, green foliage takes over, while the hazel sends up straight, dark leaved shoots.

In order to control this growth and ensure your plant retains those characteristics for which it is prized, you need to be ruthless. Not a single shoot or plain green growth on a variegated plant can be tolerated. The phormiums, which are among the toughest plants around, will barely notice if hacked back at the roots but the hazel is unlikely to withstand such abuse, which is bound to spoil its special aesthetic.

Remove the young shoots as close to their base in the rootstock as possible, while minimising damage to plant tissue. Don’t delay, as a single growing season will be decisive in deciding whether your prized mutant reverts for good or not.