American senna.

At a glance

Care level

Easy

Plant type

Perennial shrub

Light

Full sun to partial shade

Indoor light

Direct sun

Water

Every 5 to 10 days

Mature size

4 to 6 feet

Growth rate

Medium

Hardiness

USDA 4 to 8

Bloom time

Mid to late summer

Care

Plant this beauty in a spot with plenty of sun and well draining soil. Keep an eye out for yellowing leaves, which might suggest the soil is staying too wet. It is quite hardy once established and rarely needs much fuss.

Watering

Keep the soil consistently moist but never waterlogged.

Feeding

A light application of compost in early spring is usually plenty.

Pruning

Cut the stems back to the ground in late winter or early spring.

Repotting

This plant prefers to stay in the ground, but if container grown, move to a larger pot when roots become crowded.

Soil

Moist, well drained soil

Soil pH

6.0 to 7.5

Temperature

-34 to 35°C

Humidity

40 to 70%

Drought tolerance

Moderate

Lifespan

Perennial, typically 5 to 10 years.

Deer and rabbits

High

Safety

People

All parts of the plant contain anthraquinones, which can cause severe stomach upset if ingested.

Pets

This plant is considered toxic to cats and dogs if ingested.

Children

Keep children away from the seed pods, as they are tempting to touch but toxic if eaten.

Contact allergens

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

Airborne allergens

The pollen is generally not considered a significant airborne allergen.

Edibility

The seeds and pods are not for human consumption and can cause gastrointestinal distress.

How to identify it

• Pinnately compound leaves with oval leaflets
• Bright yellow five petaled flowers
• Long slender seed pods
• Upright branching stems

Height

1.2 to 1.8m

Spread

0.6 to 1.2m

Leaves

green, deciduous

Flowers

yellow, 2 to 3cm

Fruit

brown, Autumn

Problems to watch for

• Leaf spot · Fungal spots appear on leaves during periods of high humidity and poor air circulation.

Growing it

Propagation

seed, division

When to plant

Spring, Autumn

Overwintering

Cut the dead stems back to the ground in late winter or early spring before new growth begins. No special protection is needed in its hardiness range.

In containers

It is not ideal for containers due to its large size and deep root system.

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

Grows well with

• Purple Coneflower · They share similar moisture needs and look beautiful together in a summer border.
• Joe Pye Weed · Both provide height and attract a wide variety of pollinators to the garden.
• Switchgrass · The grass provides a textural contrast and structural support for the senna.

Similar species

• Wild Senna · It is very similar in appearance but generally has smoother seed pods.

Science

Family

Fabaceae

Genus

Senna

Order

Fabales

Class

Magnoliopsida

Native range

Eastern and central North America.

Conservation

It is considered secure throughout most of its native range.

It thrives in moist, open woodlands and along stream banks where it can access consistent water.

Value to wildlife

nectar source, larval host plant

Pollinators

bees, butterflies

Uses

pollinator gardens, native plant borders, soil improvement

Taxonomy resolved against GBIF.

Questions people ask

Does it need staking?

It can get tall, so planting it in a sheltered spot or with neighbors helps keep it upright.

Is it invasive?

No, it is a well behaved native plant that stays in its clump.

Where the name comes from

The genus name Senna comes from the Arabic word sana, while the species name hebecarpa refers to the hairy fruit pods.

Good to know

• It is commonly known as American senna.
• The flowers are buzz pollinated by bumblebees.
• It is a host plant for the cloudless sulphur butterfly.
• The leaves fold up at night, a process known as nyctinasty.

Also in

• Plants toxic to cats and dogs
• Deer-resistant plants