Dig It - September Tips From The Secret Gardener

Comma and hawk-moth on buddleia

Known as the Butterfly Bush, Buddleia is one of the best plants to grow for butterflies, moths and other pollinators but it must be managed to prevent it spreading across sensitive natural habitats.

The good…

Buddleia is an attractive plant with a lovely scent and beautiful purple, pink, yellow or white flowers. In July and August garden butterflies such as the Peacock, Red Admiral, Small Tortoiseshell and Comma often visit Buddleia flowers in large groups – it is clearly a favoured nectar source.  

White Buddleia and Painted LadyAt The Lavender Garden in Gloucestershire, which houses one of Plant Heritage’s National Plant Collections of Buddleia, 28 species of butterflies have been recorded, including Silver-washed Fritillary, Dark Green Fritillary and Chalk Hill Blue.

Moths such as the Humming-bird Hawk-moth can be found nectaring on Buddleia in the daytime. But it is also well worth visiting your Buddleia after dark to see night-flying species.

Buddleia is less important as a caterpillar foodplant but in May to July Mullein moths can be seen feeding. There are other polyphagous moths which use Buddleia (along with other plants). In Jennifer Owen’s book Wildlife of a Garden – A Thirty Year Study, she mentions that the moth caterpillars of 19 species fed on the Buddleia in her suburban garden in Leicester.

The bad…

Buddleia at train stationAlthough Buddleia is a valuable resource for pollinators, care should be taken to stop it from self-seedling and spreading beyond the garden, where it can out-compete native plants nearby.

Since the non-native Buddleia davidii was introduced into Europe from China in the 1890s it has spread across much of the UK and become naturalised and well-established in towns and the countryside. It can often be seen along railway lines and on waste ground. It grows vigorously and can form dense stands that eliminate other plants. This has put some wildlife at risk, particularly on brownfield sites, which are important for invertebrates. It can also germinate in crumbling brickwork and cause damage to old buildings. The cost of control can sometimes be considerable.

What you can do…

To avoid self-seeding, Buddleia should be deadheaded immediately after flowering, when all of the many nectar-containing florets on the each flowerhead have died. A Royal Horticultural Society trial from 2010-12 showed that deadheading not only improved the appearance of the plant but also extended the period of flowering and helped to prevent seedlings spreading.

All Buddleia flowering after June produce leaves on the new shoots, so need to be pruned back hard to stimulate lots of new growth and flowers.

To make the most of your Buddleia, cut it back by half in autumn, after flowering has finished, to prevent strong winds from destroying the plant.

In mid to late spring (March to April) cut it back further, to a third of its original size. This delays flowering, ensuring it blooms in late summer, just in time for the emergence of the most colourful garden butterflies.

One other thing you can do is look out for the newer varieties, which have been bred to produce fewer seeds, such as the popular Buddleia Miss Ruby, or to be sterile such as the dwarf variety Buddleia Lo and Behold ‘Blue Chip’.

Moth Night

If you have a late-flowering cultivar such as Buddleia davidii ‘Autumn Beauty’, don't forget to look out for moths around it during Moth Night (10-12 September 2015).

Happy Gardening!

The Secret Gardener