False indigo bush.

At a glance

Care level

Easy

Plant type

Deciduous shrub

Light

Full sun to partial shade

Indoor light

Direct sun

Water

Every 5 to 10 days

Mature size

10 to 15 feet

Growth rate

Fast

Hardiness

USDA 4 to 9

Bloom time

Late spring to early summer

Care

Keep the soil consistently moist while the plant is young to help it establish a strong root system. Watch for wilting during dry spells, though mature plants are fairly drought tolerant. Prune back in late winter to keep the shrub from getting too leggy.

Watering

Water deeply once a week during the first year to encourage deep roots.

Feeding

A light application of balanced fertilizer in early spring is plenty.

Pruning

Trim back in late winter to encourage a bushier shape.

Repotting

If grown in a container, move to a larger pot every few years.

Soil

Adaptable to most soil types

Soil pH

6.0 to 8.0

Temperature

-30 to 35°C

Humidity

40 to 70%

Drought tolerance

Moderate

Lifespan

Perennial, typically 15 to 20 years

Fragrance

Light

Deer and rabbits

Moderate

Safety

People

All parts of the plant are considered mildly toxic if ingested.

Children

Keep children away from the seeds and foliage, as ingestion can lead to nausea or vomiting.

Contact allergens

Handling the foliage may cause mild skin irritation in sensitive individuals.

Airborne allergens

The pollen can trigger allergic reactions in some people during the flowering season.

Edibility

This plant is not considered edible and may cause digestive upset if ingested.

How to identify it

• Pinnately compound leaves with many leaflets
• Dense spikes of purple flowers
• Bright orange anthers on flowers
• Woody stems with smooth bark
• Small curved seed pods

Height

1.5 to 4.5m

Spread

1.5 to 4.5m

Leaves

green, deciduous

Flowers

purple, yellow, 0.5 to 1cm

Fruit

brown, Late summer to autumn

Problems to watch for

• Powdery mildew · A white fungal growth on leaves caused by high humidity and poor air circulation.

Growing it

Propagation

seed, cuttings, division

When to plant

spring, autumn

Overwintering

No special winter care is needed as it is fully hardy. Simply clear away any dead debris in early spring before new growth starts.

In containers

It is generally too large for typical containers, but can be grown in very large tubs if pruned regularly.

Pair this shrub with other moisture loving natives to create a low maintenance rain garden.

Grows well with

• Switchgrass · They share similar moisture requirements and create a nice textural contrast.
• Joe Pye Weed · Both plants thrive in moist soil and attract a wide array of pollinators.

Similar species

• Leadplant · It is a smaller, more drought tolerant relative that prefers drier sites.

Science

Family

Fabaceae

Genus

Amorpha

Order

Fabales

Class

Magnoliopsida

Native range

Central and North America

Conservation

It is considered invasive in some regions outside its native range, so check local regulations.

It naturally colonizes riparian zones and floodplains, helping to stabilize soil with its extensive root system.

Value to wildlife

nectar source, larval host plant

Pollinators

bees, butterflies

Uses

erosion control, pollinator gardens, wildlife hedges

Taxonomy resolved against GBIF.

Questions people ask

Is it hard to grow?

Not at all, it is quite adaptable and grows well in many soil types.

Does it need pruning?

You can prune it in late winter to maintain its shape or encourage denser growth.

Where the name comes from

The name Amorpha comes from the Greek word for shapeless, describing the flower's unique structure, while fruticosa means shrubby.

Good to know

• It is commonly known as false indigo because it was once used as a poor substitute for true indigo dye.
• The genus name Amorpha means formless, referring to the lack of standard petals in the flowers.
• It thrives in wet soils and is often found along riverbanks in the wild.