How to grow buddleia and best varieties

Buddleia are incredibly popular with butterflies, bees and other pollinators, their spikes of tiny tubular flowers filled with rich nectar. But the plants are fast-growing and can soon outgrow their space. Recent breeding has developed dwarf varieties that should be ideal for smaller modern gardens and some that claim to be suitable for containers and hanging baskets. 

To find the best buddleias to grow, Which? Gardening magazine grew a range of new dwarf varieties to see which would give us the best display of flowers and live up to their compact claims. 

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Key facts

PLANT TYPE Shrub

POSITION Full sun or part shade

SOIL Any well-drained soil

How to grow buddleia: month by month

Best buddleia varieties

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Best Buy dwarf buddleia

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Height x spread: 75 x 100cm

This dark-blue-flowered form stood out from the rest. Its neat, compact, mounded shape makes it ideal for smaller plots or the front of a border. It flowered well in the first year producing a good display of 20-25cm long flower spikes that balanced well with the overall plant. In the second year, it bloomed better than most with the main flowering period in September thanks to the wet and windy spring.

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Height x spread: 65 x 70cm

This variety had a domed, compact habit, with narrow leaves. It produced plenty of pale pink-purple flower spikes that varied in size from 15cm to 25cm long, blooming from early July until mid-September, with a peak in early August and another at the start of September. The variable summer of 2021 affected second-year flowering, but this variety still managed a couple of weeks at peak in August.

Full testing results for buddleia

Dwarf buddleia

How we test buddleia

We planted three plants of each variety at the Which? Gardening magazine trial garden at Capel Manor College in north London; container and hanging basket varieties had controlled-release fertiliser added to the potting compost and were positioned in a sunny spot. We grew the plants for three years, deadheading as necessary and assessing them in the first and second years for flowering duration, how good a display they made and whether the plants had a compact habit suitable for small gardens or containers.  The container-grown plants were top-dressed with fresh compost and controlled-release fertiliser in the first and second spring. All plants were pruned in the second spring.

Caring for your plants

Planting 

Buddleias are relatively unfussy and will grow on rocky ground, in walls and through paving. However, your plants will be more robust and flower well if planted in fertile soil in full sun. 

Growing in pots and baskets

Some dwarf varieties of buddleja, such as the Rocketstar series and ‘Dreaming Lavender’ are ideal for growing in containers; steer clear of the Buzz varieties which are still being sold as ‘patio buddleja’, but will grow too large for most pots. Be sure to balance the size of container with the expected size of the plant to prevent it looking top-heavy. Fill your container with a Best Buy compost for pots and add some controlled-release fertiliser at planting time. Keep an eye on watering especially during hot dry conditions and deadhead regularly to keep the flowers coming. Refresh the compost each spring by removing the top layer and replacing it with fresh compost and some additional controlled-release feed.

Caring for your plants

Feed plants in the ground in spring with a potassium-rich granular fertiliser, such as rose food. Mulch to keep the moisture in, but avoid coarse woody mulches that lock up nitrogen and starve the plant. Deadhead regularly during summer to keep the flowers coming.

Pruning

Prune buddleia from its first spring in the ground. Cut back branches to around 15cm from the ground in early spring, removing any dead or crossing branches. Pruning to prevent wind rock is useful in gardens exposed to strong winds. Cut back from a third to half of the height of the plant in late autumn.

Problems

Buddleia are generally trouble free. Watch out for late frosts that can damage the emerging buds; waterlogged soil over winter can cause plants to fail.

Eelworms can be a problem in damp soil. These microscopic nematodes affect the leaves and buds causing curling and yellowing. Remove and destroy all affected shoots and leaves. 

Read more about eelworms

Downy mildew may affect the leaves in damp summers; pick off and dispose of any affected foliage.