Blue false indigo

Blue false indigo: how do you recognise it?

Habit

Shrubby, rounded clump 1–1.2 m tall and about as wide.

Leaves

Divided into three leaflets and blue-green, on sturdy stems; they darken after the first frost.

Flower

Upright spikes 20–30 cm long of pea flowers, in May–June.

Colour

Indigo to violet blue.

Fruit

Inflated pods 3–6 cm long, first green and later black; the dry seeds rattle inside.

Roots

A deep taproot with root nodules that fix nitrogen, as in many members of the pea family.

Flowering: May–June · Plants: March–April and September–October · Pruning: March

Why grow it?

• Indigo-blue flower spikes in May–June, a rare colour in the border.
• Bumblebees and bees visit the pea flowers.
• Attractive blue-green leaves that stay fresh all summer.
• Decorative black pods in autumn and winter, also lovely in dried arrangements.
• Tolerates drought and lives a very long time: a plant for decades.

Blue false indigo: where does it grow best?

• Full sun; in partial shade it flowers less and the clump falls open.
• Well-drained sandy or loamy soil, acid to neutral.
• Dry to normally moist; once rooted it tolerates long droughts.
• Allow 90 cm–1 m per plant and choose the spot for good: moving it later rarely succeeds.

Light

Sun

Soil type

Sand or loam

Acidity

Acid or neutral

Moisture

Dry or normal

Size

1.2 m tall, 1 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Oriental poppy: Orange or red flowers at the same time, a vivid contrast with the blue.
• Bearded iris: Flowers at the same time and also likes sun and dry soil.
• Switchgrass: A prairie grass that keeps the clump company later in the season.
• Purple coneflower: Also from the American prairies; it flowers later in summer.

Blue false indigo: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or in September–October, preferably a young plant in a pot.
2. Dig a deep hole so the taproot can grow straight down, and loosen the bottom well.
3. Set the plant at the same depth as it was in the pot and firm the soil.
4. Keep 90 cm–1 m away from other plants.
5. Water in thoroughly straight away, and again in dry spells during the first year.
6. No fertiliser is needed: with the help of bacteria in its roots it takes nitrogen from the air itself.

Care

Water

In dry spells during the first year. Rarely needed after that.

Feeding

Not needed; soil that is too rich makes the stems floppy.

Support

A plant ring put in place in April stops the clump falling open after flowering or rain.

Patience

For the first two or three years it grows mainly below ground. After that it flowers more every year.

Tip: Put a plant ring around the young shoots in April: the clump then stays rounded after flowering, and the black pods stand up nicely in winter.

Blue false indigo: when to prune it?

Pruning months: March.

When: In March, before the new shoots appear. Leave the black stems and pods standing all winter.

How:

• Cut the old stems off just above the ground.
• If the clump falls open after flowering, you can shorten it by a third in June; you will lose the pods, though.
• No other pruning is needed.

Caution: Wear gloves and clear up the clippings: all parts of the plant are toxic.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

The hard seed germinates better if you lightly rub it with sandpaper or soak it overnight in lukewarm water first. Sow in spring in deep pots; seedlings take a few years to flower.

Division

Only with young plants, in March: cut off a piece with root and buds using a sharp spade. Old plants do not take it well.

Blue false indigo: how does it get through the winter?

Hardy to −35 °C.

• Fully hardy, to about −35 °C: in Belgium no protection is needed.
• After the first frost the stems turn black; leave them with the pods as a winter silhouette.
• It is late to emerge in spring, often in April: mark the spot so you do not dig into it.

Diseases and pests

• Clump falling open: After flowering or rain the stems flop apart. Put a plant ring in place in April and give it full sun.
• Slow start: In the first year little seems to happen. Be patient: it gets going after two or three years.
• Powdery mildew: White powder on the leaves in late summer. Usually harmless; give it an airy spot.
• Slugs: They sometimes eat the young, asparagus-like shoots in April. Pick them off in the evening.

Through the year

• March: Cut down old stems. Plant.
• April: New shoots appear. Put a plant ring in place. Plant.
• May: Flowering begins.
• June: Flowering. The first green pods form.
• July: Green pods. Water young plants in dry spells.
• September: Plant. The pods darken.
• October: Plant. Collect ripe seed.
• November: Leave the stems and black pods standing.
• December: The black pods decorate the winter garden.

Edible and useful

Not edible. All parts of false indigo are poisonous, the seeds and pods too: they contain alkaloids such as cytisine, like broom and laburnum, which cause nausea, vomiting and stomach ache if eaten, and palpitations and trembling in larger amounts. The black, inflated pods rattle when shaken and are often used as toys or in dried arrangements: keep them out of reach of young children, who may put the seeds in their mouths. Keep dogs, cats and grazing animals away from the plant too, and do not throw trimmings into a field or pen. 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?

• Settlers in North America used it as a substitute for true indigo to dye cloth blue; hence the name false indigo.
• In the dry, black pods the loose seeds rattle like a baby’s rattle.
• As a member of the pea family, it lives together with bacteria in its root nodules, which fix nitrogen from the air.