Bladder Senna - Colutea: Planting, Pruning, and Maintenance

Botany and Description

Colutea, also known as bladder senna or bladder tree, is a genus of plants belonging to the Fabaceae family. Its name derives from the ancient Greek “kolutea”, reflecting the idea of hollow wood, in reference to its fruits: small, inflated, and translucent pods that, when dried, resemble little bladders. This genus includes about 25 species, among which Colutea arborescens, or common bladder senna, is the most widespread due to its hardiness and distinctive fruits. Colutea orientalis is also valued, particularly for its colourful flowering and more compact form.

Colutea arborescens: botanical illustration circa 1790

These bushes are particularly well-suited to dry and sunny environments. They are naturally found in Mediterranean regions, from Southern Europe to the Middle East and Central Asia. They thrive in limestone, poor, and well-drained soils, and are highly drought-resistant, making them perfect candidates for dry gardens.

Did You Know? The name “bladder senna” comes from the old French verb baguenauder, meaning “to idle” or “to wander aimlessly”. This name was given to Colutea because of its fruit shaped like small, inflated bladders, light and fun to pop between the fingers, akin to a child’s play. Indeed, the light and translucent pods, almost floating in the air, are seen as a symbol of lightness, reminiscent of simplicity and carefreeness.

Bladder senna is a bush that stands out with its bushy and airy appearance, reaching between 2 and 3 meters in height. Its habit is naturally spreading, with flexible and arched branches giving it an elegant yet somewhat disordered silhouette. This form makes it a beautiful bush for natural gardens or those in a Mediterranean style.

Its root system is taproot and robust. The plant can thus anchor well in poor and stony soils, as well as withstand periods of drought. It is a hardy plant, capable of drawing water from deep within the soil, making it a good candidate for dry gardens and arid terrains.

The foliage of Colutea is deciduous, consisting of pinnate leaves in a lovely soft green. Each leaf is made up of small, ovate and rounded leaflets, slightly velvety to the touch. This light foliage creates an impression of softness and complements its flexible habit well.

The inflorescence of Colutea consists of clusters of papilionaceous flowers, typical of the Fabaceae family. The flowers are generally yellow, sometimes tinged with orange or red depending on the variety. They bloom throughout the summer and attract pollinating insects, such as bees and butterflies, thus contributing to local biodiversity.

A graceful flowering and light foliage, and very original coppery fruits

Finally, the fruiting is one of the most striking characteristics of Colutea. After flowering, the bush produces inflated pods, shaped like small translucent and hollow bladders, which turn a reddish hue as they mature. These fruits, filled with air, are light and often burst by children. They remain on the plant in autumn, adding a decorative touch even after the leaves have fallen. These bladder-shaped pods, maturing in late summer, also provide temporary shelter for certain insects, creating small “hideaways” where they can protect themselves from bad weather or predators.

The bushy growth and flexible habit of bladder senna make it perfect for creating informal hedges, where it can blend in without the need for strict pruning. It also finds its place in naturalistic flowerbeds, where its light foliage and yellow summer flowers brighten up the plantings. Bladder senna fits particularly well in the borders of dry gardens, alongside other drought-resistant plants. As a border, it acts as a beautiful, resistant, and elegant green screen, harmonizing with the Mediterranean or wild style thanks to its hardiness and ease of maintenance.

The Most Beautiful Varieties

Colutea arborescens

Colutea arborescens originates from Southern Europe and North Africa. It is robust and easy to grow even in poor, stony soils. While not spectacular, bladder senna offers unique, decorative fruiting throughout the summer.

• Flowering time June to August
• Height at maturity 2 m

View product sheet

Colutea media Copper Beauty

Colutea (x) media Copper Beauty is a hybrid variety of bladder senna featuring a beautiful coppery orange flowering, more decorative than the bush commonly found in our southern countryside, known as the bladder tree.

• Flowering time June to October
• Height at maturity 1,75 m

View product sheet

Planting the Bladder Senna

Where to Plant?

To plant a Bladder Senna, choose a sunny location and well-drained soil, preferably limestone or stony, as it does not tolerate standing moisture. This bush is ideal in dry or rocky gardens, and it tolerates poor soils and drought conditions once well established.

Colutea does not fare well in heavy, poorly drained soils, which retain water and increase the risk of root rot, a common issue for plants adapted to dry environments. If your soil is clayey, it is recommended to improve drainage before planting the Bladder Senna by adding compost, gravel at planting, and/or planting on a raised bed.

Colutea arborescens planted here as a wild hedge (©De Tuin-Flickr)

When to Plant?

The ideal time to plant is in the autumn, between October and November, as this gives the roots time to establish before spring. In regions with harsh winters, you can also plant in early spring, but then make sure to water it regularly during the first few weeks to help the roots settle in.

How to Plant?

• Dig a hole: plan for a hole about twice as wide as the plant’s root ball.
• Gently place the root ball of the plant in the hole, positioning it so that it is upright.
• Backfill the space around the root ball with the original soil, lightly tamping as you go to secure the plant in place and avoid air pockets.
• Water generously right after planting to encourage root establishment, even if the soil is dry or well-drained. This initial watering helps the plant get off to a good start.
• Once well established, the Bladder Senna requires little maintenance. Light pruning each year will suffice, ideally at the end of winter, to encourage a more harmonious habit and stimulate beautiful flowering the following spring.

Maintenance, Pruning, and Watering

Pruning

• When to prune?: Pruning is ideally carried out at the end of winter, before the start of new growth, usually in February or March.
• How to prune?: Perform light pruning to maintain a harmonious habit and encourage flowering. Remove dead, damaged, or overly old branches, and shorten shoots that disrupt the shape of the bush. If necessary, you can also cut back more severely every 2-3 years to rejuvenate the bush, cutting down to about 20-30 cm from the soil; it will regrow vigorously.

Watering

In the first year after planting, water regularly to help the roots settle, especially in case of prolonged drought. However, once well-rooted, the Colutea copes very well with drought and hardly needs any watering, except in cases of extended severe heatwaves.

You can add a layer of mineral or organic mulch around the base to limit the growth of weeds and retain some moisture, especially in the first year.

Fertilisation

In principle, no fertiliser application is necessary. Colutea thrives in poor soils and too many nutrients might stimulate leaf growth at the expense of flowers.

Colutea arborescens

Diseases and Pests

The Colutea is a particularly hardy and resilient plant, and it is rarely affected by diseases or pests.

However, under inadequate growing conditions, such as poorly drained soil or excessive moisture, it can be vulnerable to root rot, a fungal disease that affects the root system.

In exceptional cases, it may also attract aphids, but these rarely cause significant damage and can be easily controlled.

How to Propagate the Bladder Senna?

Sowing

• Harvest the seeds from the pods at the end of summer or in autumn, once they are fully ripe. Shake the pods; if the seeds rattle inside, they are ready.
• Allow them to dry for a few days, then store them in a dry place if you are waiting until spring to sow.
• Sow the seeds in pots or directly in the ground in spring, after the last frosts. In pots, use a mix of potting soil and sand for good drainage.
• Water lightly and keep the pots in a sunny location. Germination takes about 2 to 4 weeks.

Propagation by Cuttings

• Take semi-woody stem cuttings in summer, around July-August.
• Cut sections of 10 to 15 cm and remove the leaves from the base.
• Plant the cuttings in a mix of potting soil and sand, keeping the substrate slightly moist.
• Place them in a bright area, protected from drafts. Roots should form within a few weeks.

And what about layering? Layering of the Bladder Senna, although less common, is possible. In late spring, select a low and flexible stem, bury a portion of its length in the soil and secure it with a stone or a staple. Keep the soil moist to encourage root formation. Once the roots have appeared, separate the new shoot from the parent plant and replant it in the desired location.

Successful Combinations

To create a harmonious bed around the Colutea arborescens, the common bladder senna, choose plants that enjoy the sun and well-drained soils, while bringing a contrast of textures and colours. The Lavandula angustifolia ‘Munstead’, with its grey-green foliage and violet-blue flower spikes in summer, pairs perfectly with the yellow-orange flowers of the bladder senna and creates a soothing Mediterranean atmosphere. At the base of the Colutea, the santolina ‘Edward Bowles’, compact and silvery, adds a touch of structure while harmonising beautifully with its cream-white summer flowering.

The Cistus obtusifolius, with their white flowers with a yellow heart, bring a lightness that echoes that of the Colutea, and their evergreen foliage maintains visual interest in winter. The rosemary, whose dark green foliage is dotted with small blue flowers, not only adds an aromatic dimension to the bed but also forms a beautiful companion contrasting with the Colutea. Alternatively, the Afghan sage, like the Perovskia ‘Blue Steel’, with its violet-blue flowers and fine foliage, creates a visual depth that accentuates the bright yellow of the bladder senna.

Finally, the Thymus praecox ‘Coccineus’, used as a ground cover or border, forms a verdant, evergreen, and fragrant tapetum, which perfectly complements the flexible and airy habit of the Colutea. Together, these plants create a natural, colourful ensemble perfectly suited to drought conditions, for a garden that is both vibrant and easy to maintain in well-drained soil and sun.

Colutea arborescens, Lavender ‘Munstead’, Cistus obtusifolius, Santolina ‘Edward Bowles’, rosemary, Perovskia ‘Blue Steel’ and Creeping Thyme ‘Coccineus’