When I was a child in the Yorkshire Dales, buddleia meant to me that big bush with orange bobble flowers, which as a teenager I came to know as Buddleja globosa, from Chile. It had flowers like a pawnbroker’s balls, but held the other way up, and the plant was tough as old boots; wind could not break it. It was a big shrub, up to 12ft, and it had to be pruned after it flowered in summer, since the flower buds came on last year’s growth, like a hydrangea’s.
It was only later that I came to know the far more common Buddleja davidii from China; the butterfly bush. I met it in gardens and then, to my amazement, I found that this was the plant so rampant in the gravelly rubbish of railway embankments. There it was too, self-sown into high street chimney stacks where the pointing was weak, living on no more than rainfall and its luck.
Clearly this was a group of plants to watch. I met others: Buddleja alternifolia, a rangy, droopy, willowy shrub with fragrant lilac flowers, also from China; I met the tender B. auriculata from South Africa, a rambling evergreen with white-felted leaves and seriously fragrant white flowers; B. asiatica from Nepal to the Philippines, a small tree with perfumed white flowers in winter. What a family! And then there was Buddleja x weyeriana, the result of incest between my old friend B. globosa and the ubiquitous butterfly bush.
Which would I prefer to grow now? If I had a warm wall and plenty of space, certainly B. auriculata. But for sheer garden value I settle for the butterfly bush, Buddleja davidii. You can find it in various colours: blue, mauve, purple, magenta, white, pink(ish). There are more dwarf forms (such as the “Pixie” series), blue-flowered, grey-leaved “Lochinch” (another indiscretion, this time with Buddleja fallowiana), and “Dartmoor”, found there in 1971, and whose maroon flowers are heavily branched.
But how to grow the butterfly bush well? You might say give it poor soil — it likes it — but if you are pruning away 80 per cent of its growth now, every March, then it’s got to have some decent nourishment to start again. You might say give it very dry soil (that chimney stack), but if you do, it tends to lose leaves at the centre of the bush in midsummer and looks pinched. All it really wants is some decent garden soil in full sun, and a regular feed, immediately after pruning, with a balanced fertiliser. A nitrogen-heavy fertiliser will make it grow like crazy, but the new shoots will be so lush that they’ll blow off in the wind.
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How far to prune? It depends on what you want it to do. You can cut it back to 6ft, to make a 10ft fountain of growth at the back of a border or against a fence. You can cut it to 3ft-4ft and create a more modest, rounded bush. (You must scale all this down for the dwarf forms; the “Pixies” make 5ft-7ft; “Blue Chip” 2ft.) Most important is that you prune purposefully. What you are after is a framework of older stems — trunks, if you like — arranged in a V-shape that is open at the centre, so the new shoots will criss-cross as little as possible. For a few years at least you can cut back to exactly the same point, the same stump, and new shoots will come from nearby and below. Every year a few new stems will appear from nearer the ground, and if some of the arms of your V are getting ancient and craggy, you can saw one out and let the new shoot replace it.
When you prune off all last year’s long wands of growth, you’ll take with them dozens of fat emerging shoots. Don’t worry; more will come from below. And if there are too many shoots appearing near ground level, you can rub them off too. If the plant is entirely leafless after pruning, it’s no problem. In fact, the more I think about it, the more I see that you can’t go wrong. The important thing is just to cut, and to cut every year. Otherwise you’ll be overwhelmed. But even when its trunks are fat as your thigh, you can take a chainsaw and carve it back. It will come again; I’ve tried it. I was gleeful, then pleasantly surprised.