Bladder senna

Bladder senna: how do you recognise it?

Habit

Loose, upright to slightly arching shrub 2–3 m tall and as wide; fast-growing.

Leaf

Pinnate, with 7–13 oval leaflets of 1–3 cm, matt grey-green; drops in autumn without much colour.

Flower

Yellow pea flowers of about 2 cm, often with red markings on the upper petal, in clusters of 3–8, from May to August.

Fruit

Inflated, papery pods of 5–8 cm, pale green at first, later reddish to brown; they pop when squeezed. The seeds are poisonous.

Roots

Deep, with nodules in which bacteria fix nitrogen from the air; that is why it grows in very poor soil.

Flowering: May–August · Plants: March–April and October–November · Pruning: March

Why grow it?

• Flowers for months, from May into August, while the first pods are already hanging on the shrub.
• The inflated pods are eye-catching from summer into autumn.
• Bumblebees and bees visit the flowers.
• Grows in poor, dry, chalky and stony soil and copes well with drought and heat.
• Fast-growing: ideal for quickly filling a bare spot, a bank or a new garden.

Bladder senna: where does it grow best?

• Full sun: that is where it flowers best and stays most compact.
• Any well-drained soil: sand, loam or clay, neutral to chalky. Poor, stony, dry soil is ideal.
• No wet or boggy soil.
• Allow 2–3 m per plant; in an informal hedge plant 1.5 m apart.

Light

Sun

Soil type

Sand, loam or clay

Acidity

Neutral or chalky

Moisture

Dry or normal

Size

3 m tall, 3 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Russian sage: Blue spikes next to the yellow flowers, in the same sunny, dry spot.
• Globe thistle: Steel-blue globes for bees and a bold contrast.
• Lavender: A fragrant, low foreground on dry, chalky soil.
• Feather grass: Airy stems that move in the wind, next to the fine, grey-green leaves.

Bladder senna: when and how to plant it?

Plant in March–April and October–November.

1. Plant in March–April or October–November, when the soil is not frozen or too wet.
2. Dig a hole twice as wide as the root ball; compost or fertiliser is not needed.
3. Set the plant at the same depth as it was in the pot and firm the soil well.
4. Water in thoroughly straight away and water in prolonged dry spells during the first year.
5. Spread a layer of gravel or wood chips around the base to keep weeds down.

Care

Watering

Only in dry spells in the first year; after that it copes even in dry summers.

Feeding

Not needed: it fixes its own nitrogen. Fertiliser gives long, floppy branches and fewer flowers.

Pods

Leave them on for decoration; cut them off if you do not want seedlings.

Seedlings

It sometimes self-seeds on bare soil. Pull up young seedlings in good time.

Shape

Prune it every spring (see pruning), or it soon becomes untidy and bare at the base.

Tip: Prune it firmly every year in March: it stays compact and flowers well on the new shoots. It belongs in a poor, dry spot; in rich soil it mainly makes leaves.

Bladder senna: when to prune it?

Pruning months: March.

When: In March, before the shrub comes into leaf. It flowers on this year’s shoots, so spring pruning costs no flowers.

How:

• Cut back last year’s shoots to a few buds above the older wood.
• Remove dead, weak and crossing branches.
• A shrub that has gone bare can be cut back hard, to 30–50 cm above the ground: it usually reshoots well.
• For a smaller shrub, prune firmly every year rather than very hard every few years.

Caution: Do not prune in summer: you would cut off flower buds and pods.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Collect ripe seeds in autumn. In spring, soak them overnight in lukewarm water and sow them in a pot or seed tray; they germinate readily.

Semi-ripe cuttings

In July–August, take 10 cm cuttings from side shoots and put them in sandy cutting compost under plastic or in a cold frame.

Bladder senna: how does it get through the winter?

Hardy to −25 °C.

• Fully hardy, to about −25 °C: no protection is needed in Belgium.
• In a severe winter the tips of young shoots may be frosted back a little; cut them off when pruning in March.
• It is less suited to a pot: it grows large and roots deeply.

Diseases and pests

• Leggy and untidy: Without pruning it becomes tall, bare at the base and falls open. Prune every year in March.
• Seedlings: It self-seeds on bare soil. Cut off the pods or pull up young seedlings in good time.
• Aphids: On young shoots in spring. Ladybirds usually deal with them; otherwise spray them off with water.
• Root rot: On wet soil it declines and branches die back. Plant it in a dry, well-drained spot.

Through the year

• March: Prune: cut back last year’s shoots. Plant.
• April: Plant. Mulch.
• May: Flowering begins.
• June: In flower; bumblebees on the flowers. The first pods appear.
• July: Flowers and pods together. Take semi-ripe cuttings.
• August: Last flowers. Water young plants in prolonged drought.
• September: The pods turn reddish to brown. Collect seed.
• October: Plant. Cut off the pods if you do not want seedlings.
• November: Plant.

Edible and useful

Not edible. The seeds and leaves of bladder senna are poisonous and cause stomach and gut upsets. Children love popping the inflated pods: that is fine, but teach them that the seeds inside are not peas and must not be eaten. The leaves were once used as a laxative instead of senna (hence the name): do not make tea from them. Keep grazing animals away. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Its Dutch name, blazenstruik, means ‘bladder shrub’, after the pods that are inflated like little bladders.
• The French verb ‘baguenauder’, to fritter time away, comes from ‘baguenaude’, the name of its pod.
• There is a related hybrid, Colutea × media, with orange-red to coppery flowers.