How to grow Buddleja (Butterfly Bush)
Buddleja, a very easy to grow summer flowering garden shrub. Buddleja are evergreen, semi evergreen and deciduous; the most commonly grown is B.davidii (image left) which is deciduous. Buddleja davidii is fast growing and a large shrub, up to 5m with 5 m spread, but easily kept in check by pruning and Buddleja benefit from a hard prune late winter. Buddleja is grown for it's lovely panicles of flowers, often scented, and which are attractive to insects and butterflies. B.davidii is *** hardy suitable even for cold exposed areas and for costal gardens. Buddleja has many attractive colours 'Black Knight' which is dark purple, 'White profusion,' 'Harlequin' pink which also has variegated leaves, and 'Empire Blue'. Buddleja requires no real attention to survive and is not fussy as to soil types, growing especially well on chalk and lime soil, and it is easily grown even on poor soil.
Buddleja alternifolia, which is also deciduous, and has lovely scented lilac coloured flowers in early summer .
Buddleja is known as the butterfly bush and rightly so. In the summer it is full of butterflies, bees and insects. The image top left is one flower with three peacock butterflies on it all at once. If you grow Buddleja in your garden you will be able to enjoy butterflies flitting around. A good combination would be to plant Buddleja with Oregano and Sedum and create a butterfly paradise.
Recently Buddleja has had a bit of a bad press as being invasive because of self seeding, particularly if your garden is near an area of natural beauty or conservation. If this is a worry dead head flowers which will prevent it setting seed.
Best varieties of Buddleja to grow
A good starting point is the RHS garden merit shrubs with this logo
Buddleja davidii Nanho White 'Monite' scented compact up to 1.5m
Buddleja davidii Nanho Purple 'Monum' around 2.smaller pruple flowers
Buddleja davidii 'Black Knight' scented very dark purple up to 3m.
Buddleja davidii 'White Profusion' large up to 4m and scented
Buddleja davidii 'Royal Red' large up to 4m scented red flowers
Buddleja 'Pink Delight' up to 4 m smaller pink flowers
Buddleja davidii 'Darent Valley'
To name just a few, and there are plenty to choose from. Secondly, to be on the safe side cut back the flower heads after flowering to prevent seeding.
Buddleja provides lovely later summer colour and look well planted with other silver foliage plants such as Nepeta, Artemisia, also with tall grasses such as Stipa. There are some very compact Buddleja suitable for containers and patios such as such as B. Buzz, Blue Heaven, free petite dark pink, lavender white and blue, and B. morning mist. More compact varieties are being introduced to the market all the time and the compact varies grow well as container plants.
How to prune Buddleja
Buddleja davidii flowers best if hard pruned in late winter or early spring, around March time, either close to the ground, or down to woody framework which also helps to check its overall size. It will look a bit sparse when first pruned, but it is best to be bold and it will spring back into life and shoot up. Buddleja davidii should be pruned when the worst of the weather is over, later in Feb/March and it is a drastic prune; cut off all of last year's growth close to the ground to where you can see buds breaking. It is not essential, the shrub will survive well if not pruned, but pruning produces the best flowers and keeps it to size. If it is not pruned over time it will get very large and the flowers small and fewer.
The other common type of Buddleja, B. alternifolia is pruned differently and requires pruning after flowering. It flowers in early summer and so it needs to be pruned later in summer after flowering. This is because it flowers on the same year's wood so it is cut back after flowering to allow growth over the ensuing months on which the flowers will grow. B davidii is different flowering on new growth and so the two types of Buddleja need to be distinguished. B davidii flowers on new growth and so is cut back in Feb/March to create the new growth on which it will flower. With B.alternifolia do not prune as hard, just cut back the flowering stems, and it will form a large weeping shrub or small tree in time.
How to tell which Buddleja you have?
Buddleja alternifolia has alternate leaves, it is deciduous with a weeping shape and it flowers are light mauve appearing in late spring and early summer. The leaves have a silver tinge and it is less common than B. davidii.
B.daviddi flowers later in the year from August onwards and has flowers different colours which include light mauve, but also many shades of purple, dark purple, red, and white. It is arching in habit as compared to weeping. If you are not sure which Buddleja you have in your garden, the flowering time is the best indicator.
B.davidii is considered by some to be invasive so it is best to dead head flowers to promote more following but also to prevent the shrub setting seed.