Some plants are easy to kill; others are naturally short-lived. ‘They flower themselves to death,’ we say.
Botanists may argue over whether foxgloves are biennials or short-lived perennials, but what about shrubs? Why do Ceanothus and Cytisus conk out unexpectedly just when they seem to be thriving? One moment, they fill a joyful space in the garden and the next, they leave a gaping hole.
All this came to mind while I was contemplating the skeleton of my white-flowered Daphne mezereum, a sweet-scented shrub that starts into flower shortly after Christmas. Because there’s another daphne that’s even more unpredictable. D. x houtteana should be hardy, tough and adaptable, because it’s a hybrid between two native plants – purple-pink D. mezereum and evergreen D. laureola – and it combines the best characteristics of both its parents. What’s more, the leaves turn purple as they expand, a shade so dark that they sell it in the USA as the ‘black-leaved daphne’.
Daphne x houtteana has a long history. It was bred by the erudite and energetic Louis van Houtte (Belgium’s answer to Sir Joseph Paxton) and released in 1850. It was never very common in gardens, but it roots fairly easily from cuttings, so it survived and passed between gardens in the way that plantsmen’s plants do.
Nevertheless, it dwindled away over the decades, so that, by the time Chris Brickell and Brian Mathew wrote their important monograph Daphne: The Genus in the Wild and in Cultivation in 1976, neither of them had actually seen a plant of it. In those difficult days before the RHS Plant Finder, many people thought it extinct.
Probably the last plant of it in England was, at that time, flourishing in the garden of the remarkable Wiltshire plantsman John Phillips. He knew it was rare and wondered whether he could persuade a nurseryman to take an interest in it. Its commercial potential was considerable – it was neat, winter-flowering, scented and more or less evergreen, with purple leaves, but, above all, it was a small shrub for small gardens. It fitted the spirit of the times exactly.
Although still in its infancy 40 years ago, micropropagation was the salvation of this daphne. Mr Phillips sent suitable pieces to a lab and it turned out to be easy to multiply this way. Soon, it was offered for sale in surprising quantities – one wholesaler quoted his price for multiples of 10,000.
Suddenly, it seemed that everyone grew it. Daphnes are, however, short-lived and we all discovered that D. x houtteana usually dies before it reaches 10 years old. It was no longer to be found in everyone’s gardens, nor was it so ubiquitous in nurseries.
Pondering the bones of my dead D. mezereum Album, I decided to replace it with D. x houtteana, wondering whether I might die before it did.
But could I find it? The Plant Finder told me that only one nursery in Britain still listed it: Karan Junker’s splendid home for rare trees and shrubs in Somerset. She replied: ‘We [do] have it… but… it is not growing strongly enough to give us propagation material… although we propagate a few when we can, it’s rather sporadic and there are none currently available.
I asked Mr Brickell for his views and he suggested that viruses might explain the second disappearance over the past 30 years. They’re a problem with many plants, but they’re invariably cleaned up as part of the process of micropropagation.
I suspect that, when the micropropagated plants went into gardens, they picked up new viruses that weakened them rather more than the old ones. Perhaps the old ones gave a measure of protection against the consequences of further infection.
However, he added, the cross may be inherently weak because its parents evolved for different environments and are too distantly related. So much for hybrid vigour!
The good news is that the German expert on daphnes, Dirk Jockel, has recently succeeded in remaking the original cross. His plant has the same dark-purple leaves, but its flowers open greenish- white before turning purple, so he’s named it Chameleon.
Its existence is encouraging, but, as yet, no one has it for sale. Let’s just hope it’s not too easy to kill.
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