How to grow buddlejas

Choosing a buddleja

There’s a lot of variety to choose from in buddlejas. However, if you want to keep it simple, choose a Buddleja davidii in a colour you like, as these grow well in most gardens. Then, if you are interested in growing some of the other buddleja available, it helps to bear in mind the following things:

Height

Many buddleja make tall shrubs, 2.5-3m (8-10ft) tall, even with hard annual pruning. If you have a smaller patch, or are looking for something for the front of the border, or a container try one of the dwarf cultivars of B davidii like the Buzz series or Nanho series. These typically reach 1-1.2m (3-4ft) tall. 

As well as being grown as an upright or umbrella-shaped bush (e.g. B. davidii  and B. x weyeriana), it is possible to grow buddleja as lollipop-like standards. B. alternifolia is an ideal choice to be grown on a stem as a standard, but you will also see B. davidii sold in this form.

Colour

You can choose from a range of flower colours and their shapes range from slender spikes to rounded clusters.

• Hardy in the garden:  B. davidii offers flower colours from white to pink, lilac, blue and crimson, the weeping B. alternifolia with lilac flowers or the orange-flowered B. globosa and its hybrid B. x weyeriana.
• For a sheltered or urban site: try the grey-leaved, pale-mauve flowered B. crispa, or the exotic red-flowered B. colvilei. 

Hardiness

• Buddlejas that are fully hardy in the UK (a hardiness rating of H5 and higher) can be planted anywhere sunny in the garden. This group includes B. alternifolia, B. globosa, B. x weyeriana, B. davidii and its cultivars
• Some buddleja are hardy in most parts of the UK but, in severe winters, will need some protection such as being by a south-facing wall or temporarily insulating with horticultural fleece (generally a hardiness rating of H4). Examples include B. crispa and B. colvilei.
• Tender buddeleja, such as B. madagascariensis and B. asiatica, need to be kept in a conservatory or at least to be container-grown and brought in to frost-free greenhouse for winter (hardiness ratings H3 and H2). 

Whatever your preferences, consider going for buddleja that have received the RHS Award of Garden Merit as these have been tested and perform well in average garden conditions

Buying buddlejas

You can expect to buy buddlejas in 2-3 litre or larger containers at any time of year from garden centres and nurseries. Ocassionally you'll also find smaller potted plants available – they just take a year extra to grow and flower well in the garden.

If you really get into buddlejas, there's a National Collection to visit in Hampshire. They also usually offer plants for sale.

To find buddleja that are available to buy near you, or to find a specific plant, use RHS Find a Plant

Where to plant

Plant hardy buddleja (see Before you get started above) in ground in a sunny spot– one that receives good light for most of the day –  as they will flower best here.  

Avoid very windy sites, even for hardy B. davidii as the long branches are likely to snap off in summer gales and rock the whole bush, opening up a gap in the soil around the base exposing the roots.

Do also read the plant label to find out the full-grown size of the plant and give it the space it needs to grow. Annually hard pruning B. davidii and B. x weyeriana will keep them in check to about 1.8-2.4m (6-8ft) – smaller if its a dwarf cultivar. These smaller plants can also be grown in containers.

When to plant

Hardy buddlejas can be planted at any time of year, but you’ll need to water them well if you plant them in summer in full leaf. Planting in spring is ideal as the warm, moist conditions will help them establish.

With the less hardy or tender buddleja, planting in spring is best as the worst of the winter cold is over.

How to plant

In the ground: Buddleja are planted the same as any shrub. The general aim is to dig a hole just deep enough to take the rootball, but two or three times wider. Improve the soil you dig out with some well rotted garden compost or manure and firm this back around the roots. The rootball should be just below the soil surface when you have finished. Water in well and keep the soil moist but not soggy while the plant established (this typically takes 18 months).

In containers: Planting dwarf buddlejas in a container, use a peat-free multipurpose potting compost with added John Innes. Add some slow-release fertiliser to the compost to provide feed for the first summer. Repot every two to three years to ensure good growth. They'll eventually need a large pot approximately 60cm (2ft) wide.

RHS guide to how to plant a shrub

RHS guide to how to plant a shrub

Watering

Water plants in the 18 months after planting until established, aiming to keep the soil moist but not soggy. They should be fine after that. An annual 5cm (2in) layer of mulch will help conserve moisture.

Feeding

On a fertile soil, no feeding is required. An annual mulch of organic matter such as well-rotted manure or garden compost will suffice. For container grown plants, add some slow-release fertiliser annually to keep them flowering or use a liquid feed between April and September according to the instructions.

Deadheading

You can deadhead after flowering to remove the brown flower heads and improve the plant's appearance. This may also promote a second flush of small flowers.

Overwintering

No special treatment is required in winter unless you are growing one of the less hardy species that requires winter protection. If these are plants growing in the ground, you may want to wrap these plants in fleece in a very cold snap. Less hardy buddleja in pots can be brought into a cold greenhouse or conservatory for protection.

Most buddleja flower on the branches that grow in early summer, so can be pruned hard to a low framework of permanent stems in early spring (late March-mid-April). Examples include: B. davidii, B. x weyeriana, B. fallowiana, B. salviifolia and B. crispa (but this last one benefits from being on a taller framework).

For plants that flower on last year’s wood, prune after flowering – usually in early to mid summer. Examples include: B. alternifolia, B. colvilei. 

B globosa only needs little pruning, but you can cut back overly long branches in late winter. This will reduce that summer's flowering, but maintain vigour and keeps the plant in shape.
 
A few species can be trained as wall shrubs, for example, the winter flowering, tender B. madagascariensis, B. auriculata (and is a good idea even the hardy B. crispa and B. fallowiana  if your garden is in a colder part of the country and therefore they need more protection).

Pruning standards

If you have a standard buddleja, you also prune the head hard back to the top of the stem/trunk in early spring. The head will then regrow in early summer.

If you are growing the weeping B. alternifolia  as a standard, you may have to train a bushy new purchase. Select an upright stem as your main trunk and tie to a cane.

Buddlejas are propagated by softwood or greenwood cuttings in early summer and semi-ripe cuttings from mid-summer. They root readily. You can also try hardwood cuttings from autumn to mid winter. They should be ready to plant out in the garden in a couple of years.

Buddlejas are generally problem-free, but watch out for late frosts on less tough species.

In cold, waterlogged conditions, you may find that even the hardy buddleja (B. davidii) will fail. This is largely due to the roots rotting in the wet soil over winter. Where this is a problem, try planting near a house wall where it's sheltered, or in a raised bed as this will lift the roots out of the water in winter.