It’s nearly a month since I wrote my last blog post, because the weather has been sunny and warm and I’ve spent quite a bit of time out and about looking for butterflies and other insects. I have photographed many of these on Buddleja bushes in various parts of Norfolk. It is not surprising that the most commonly grown species, Buddleja davidii, is known as the Butterfly Bush.

Red Admiral butterfly on Buddleija davidii

I tend to spell Buddleja with an “i” – “Buddleia” – and this was the spelling I grew up with. However, Linnaeus used the spelling Buddleja and this has now been adopted as the correct spelling. The genus Buddleja is in its own family, the Buddlejaceae, and the name was given to commemorate the Reverend Adam Buddle (1662–1715), an English cleric and botanist who spent much of his life in East Anglia.

Buddleja davidii comes from China and is one of a number of shrubs in the genus. It grows easily in gardens, preferring a sunny spot, though even in shade its tall branches can grow up into the sun within a season. Flower spikes are produced in July, August and September at the top of the same season’s growth. The flowers are strongly scented and can be a bit overpowering on a hot sunny day. Outdoors they are pleasant but in a vase indoors their presence rapidly overpowers and I’ve only tried them as cut flowers once, for about an hour.

Left to its own devices, a Buddleja davidii bush can grow very large. New shoots grow outwards and upwards each year and soon the flowers are about fifteen to twenty feet (4 – 6 metres) tall and too tall to see any insects (especially butterflies) that are attracted to them. It is a good idea to prune the bushes every year, to about a foot (30cm) from the ground. This can be done in autumn or early spring – I cut mine in March. Cut stems can be used as hardwood cuttings in winter, if you want to propagate. They are very easy to grow: I use my Buddleja sticks to mark rows of seedlings on my allotment and a few of these markers sprout leaves every year! Cuttings are a good way to produce plants with the same flower colour as the parent, if you have a cultivar you particularly like. Buddleija davidii produces copious seed in the south of Britain, but the resulting plants will usually have pale mauve flowers.

Since Buddleija davidii self-seeds so readily, it can become a very invasive plant in urban areas and on waste ground or on railway tracks. The species was introduced to Kew Gardens in 1896 and was growing in the wild in the UK by the 1920s. In 2008 DEFRA estimated that Buddleja costs the British economy £961,000 per year, because it damages old buildings and has to be cleared from railway tracks. Maybe this isn’t entirely bad: a Buddleja seeded into our chimney on our previous house and cost us money (bad for us) but it also provided employment to a local handyman (good for him and the local economy). Butterfly Conservation have produced a very sensible Position Statement about Buddleja davidii, which suggests ways to use the plant to encourage butterflies without it becoming a nuisance. The RSPB also give advice, including alternative plants for attracting butterflies. I find that Verbena bonariensis is especially attractive to butterflies, even when a Buddleja davidii is in flower right beside it.

Buddleja davidii is also an invasive species in some other parts of the world and is banned in some parts of the United States. On her Toronto Gardening All Year Round blog, Rosemary Waigh recommends some alternative plants for attracting butterflies in the United States and Canada.

Buddleja seeds are appreciated by birds but if you’re concerned about the plant spreading, you can remove the spent flowerheads when they turn brown, which also makes the plant flower longer. (Seeds don’t develop until late winter.) If you prune some bushes in autumn and some later in spring you will also prolong the flowering season.

There are other, more refined, varieties of Buddleja. Buddleja x weyeriana is the name given to hybrids between Buddleja davidii and the spring flowering “Orange Ball Tree”, Buddleja globosa. Flowers of B. x weyeriana are intermediate between the two parents, but the flowers are produced slightly later than Buddleja davidii. Flower colour varies, so it’s a good idea to look for one in nursery or garden centre in August, so you can see the flowers before buying. Variety ‘Sungold’ is one of the loveliest, with clear yellow flowers. We grow a form with a mix of mauve and yellow in the flowers, perhaps a variant of ‘Moonlight’. Ours attracts butterflies and bees just like B. davidii. Growth and pruning are like B. davidii. Not everyone is a fan – the late Christopher Lloyd wrote that B. x weyeriana “combines the worst features of both parents in a sickly orange, pink and mauve vomit.” I think that was very unkind, but you can decide.

Buddleja globosa flowers in early summer and for this reason I have rarely seen butterflies on the blooms, though the flowers have plenty of nectar and are loved by bees. The shrub needs very little pruning.

Bumblebees on Buddleja globosa

We also grow Buddleja alternifolia. This is an elegant plant, though it can grow as big as any other Buddleja (3 metres high and 4 metres across). It has smaller, alternate leaves which look a bit like willow, and elegant arches of pale mauve flowers. The flowers are produced on the previous year’s shoots in late spring, so pruning is very different from Buddleja davidii. As with B. globosa, bees like the flowers. The species is not invasive in the UK.

A fine specimen of Buddleja alternifolia, in the Bishop’s Garden in Norwich.

There is a lot of other interesting information on different species and varieties of Buddleja on the web. I can recommend the The Telegraph’s article “The Butterfly Effect: blossoming buddleia” and the Urban Butterfly Garden and The Buddleia Garden websites. The Plants for a Future website reports no known uses of Buddleja for human food or medicine, but the flowers can be used to make dyes.