Give me a B, a U, an I, an S! Who I am ? Boxwood! Who is that ? Boxwood! Who, who, who? THE BOXWOOD! Many of you here probably know this little shrub, a real rock star of the most beautiful French, Italian or English gardens. What you may not know is that the famous little plant is threatened with extinction. To the point of endangering the perfect geometric shapes of the most beautiful parks and castles in France? Let’s be honest, it’s not impossible. Boxwood might even have already disappeared without the constant mobilization of enthusiasts. With the arrival of spring, gardeners have even gone on red alert. Their objective: to spot the arrival of the dangerous boxwood moth as early as possible.
“It is an indispensable plant, essential to our gardens. However, I have seen entire gardens destroyed. So yes, it worries me, but we fight every day to preserve it. » Giovanni Delu is the head gardener at the Grand Trianon in the prestigious grounds of the Palace of Versailles. Here, boxwood is a treasure that should not be shared with pests. Used for centuries to create pretty borders, the shrub was not chosen at random by the gardeners of Henry IV, Louis XIII or Louis XIV. “It grows slowly, it resists pruning well, it has a regular and uniform growth which means that it does not go up in stem. In addition, it is quite easy to reproduce and adapts to both sun and shade and resists drought. Before the arrival of the moth, he was doing very well,” summarizes the head gardener of Versailles.
Originally from Asia, this caterpillar was observed for the first time in Europe in 2007, according to the National Research Institute for Agriculture, Food and the Environment (Inrae). “In the space of ten years, it colonized a large part of the European continent, posing a threat to native buxus berries. [forêts de buis] and French gardens”, recalls Inrae. Faced with the voracious appetite of this butterfly larva, several treatments have been tested. The most common is called “Bacillus thuringiensis” or “BT” for short.
“We can’t do without”
Compatible with organic farming, this product turns out to be formidable. But it remains an insecticide, incapable of distinguishing between “good” and “bad” caterpillars. “It still has an impact on biodiversity so we limit it as much as possible,” assures Giovanni Delu. “You have to be honest. We can’t do without it,” says Françoise Mathiot-Mathon, a true lover of boxwood. The owner from the castle of La Ballue (Ille-et-Vilaine) employs three gardeners to maintain two hectares of garden. Everyone is trained to detect the dreaded pest. Each time they disembark, they take out their sprayer.
The biggest weapon that gardeners have to fight against the moth, however, turns out to be much more natural than chemical treatment: their eyes. Every day, these enthusiasts scan the leaves of the boxwood to watch for the appearance of the first eggs. Pheromone traps are also used to capture butterflies, but above all they allow them to anticipate a laying period. “It’s permanent surveillance! It requires a lot of work. There are people who say they can’t take it anymore and I understand them. When you have boxwood, you can’t really take a vacation. Because when the moths attack, you have to react immediately. But I want to tell people: fight! Because boxwood is worth it,” harangues Françoise Mathiot-Mathon.
In Rennes, we preferred to let it go
Throughout France, some owners preferred to give up after having suffered the appetite of hungry caterpillars. In Rennes, the gardens and biodiversity department had to resolve to abandon its favorite species, which still represents 4 km of plantations in the charming Thabor park. Plant alternatives such as crenellated holly, ivy or shrubby honeysuckle have been well studied but “they prove too imposing for such small borders”. Instead, the city decided to install woven steel curbs. Less maintenance, less hassle.
To avoid reaching such a situation, owners multiply the “small gestures” of everyday life intended to limit the risks. “At home, we have no night lighting because the light attracts butterflies,” advises Françoise Mathiot-Mathon, also a member of the very serious EBTS, the first European association of garden lovers. Giovanni Delu agrees and adds some other advice, valuable for fighting against the other major predator of boxwood: the fungus. “At the Grand Trianon, we don’t treat it, we accept it. But we redouble the maintenance to remove dead wood and have a well-ventilated hedge, which will limit humidity and the development of fungi. » Again, work.
Since its adoption by gardeners in the 17th century, boxwood has always been the subject of great attention from gardeners. “At the time, they were regularly changed. The problems are not new,” recalls Françoise Mathiot-Mathon, who can boast of having 300 varieties in her gardens. Weakened by its predators, the species was able to count on the inventiveness of enthusiasts to better resist. By developing new, more resistant varieties, gardeners have armed the plant to fight better. And undoubtedly saved the French gardens that the whole world envies. Long life to boxwood.