Gardening: Olive fans, don’t risk it

16 August 2019

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THAT quintessential Mediterranean tree, the olive, is under threat from a bacterium, Xylella fastidiosa, that blocks the plants’ water-conducting vessels causing dieback and death. It is spread by insects, and is affecting trees in France, Spain, and some Mediterranean islands. It is wreaking havoc in the Puglia region of Italy, threatening olive farms that have been a family’s livelihood for generations. The ubiquitous nature of olives in the Mediterranean countryside makes the problem acute. A monoculture of millions of trees allows rapid spread of the pathogen, and what is lost is everything to a poor rural community centred on oil production.

For us Northern Europeans returning from a holiday in the south, it is tempting to bring back a living horticultural souvenir. Many plants evocative of sun-soaked days, not just the olive, are on a long and growing list of possible hosts for Xylella, notably rosemary and lavender. It is still legal to bring these plants back from an EU destination if they are “pest and disease free”.

A long incubation period before symptoms appear and the likelihood of carrier plants in which they never appear are both challenges facing plant health professionals dealing with xylella. A tourist will have no clue. This makes the advice from the Department for Environment, Food and Rural Affairs particularly pertinent: “Don’t Risk It!” We must make notes of plants spied on holiday and source them from a reputable supplier back home. In the case of the olive tree, that might become harder and more expensive in time.

Some nurseries have already put in place a self-imposed ban on stocking olives, despite their enduring popularity. An all-out ban on importing trees would certainly level the playing field, but may be avoidable through tightly controlled trade with non-infected regions and regulated quarantines.

Perhaps this is our cue to question the olive as a desirable garden plant for the UK. In the microclimate of central London and mild south-western gardens they perform well. Elsewhere, however, their symbolism possibly blinds us to their real climatic needs, and we let them limp on year to year. An alternative that will thrive rather than cope is Eucalyptus kybeanensis: a small, hardy evergreen tree with a light silvery canopy of leaves. Or there is Phillyrea latifolia, closely related to the olive, and also from the Mediterranean basin, but hardier.

If you dismiss its deciduous nature, the willow-leaved pear, Pyrus salicifolia Pendula also makes a tough stand-in for an olive tree. The Russian olive, Elaeaganus Quicksilver, although more of a large shrub than a tree, creates a similar effect. With its intoxicating scent released from the spring flowers, and light-reflecting foliage, it has prompted more compliments and questions than any other plant in my garden this year. More, even, than my olive.

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