perennialN. America Native

Herb-Robert

Geranium robertianum

The Story

Plant Bio

Geranium robertianum is a low-growing, branching annual to short-lived perennial herb with sprawling to erect stems that frequently flush reddish-purple. The deeply divided, fern-like foliage emits a strong, musky odor when crushed, and pairs of small, deep pink to magenta flowers appear from spring through fall.

This species is distinguished by its highly active self-seeding mechanism, utilizing explosive seed capsules to project seeds several yards. In many regions outside its native northeastern North American range, such as the Pacific Northwest, it behaves as an aggressive, carpet-forming woodland weed.

Uses & Benefits:

Provides delicate, deeply divided foliage that flushes reddish-purple alongside small pink flowers.

Functions as a quick-growing groundcover in dry shade where other plants struggle to establish.

Attracts generalist native pollinators, including various species of bumblebees.

Essentials

At a Glance

Plant Type

Perennial

Height

16"

Width

16"

Light

Full Sun, Partial Sun, Shade

Zones

4, 5, 6, 7, 8

Water

Moderate to low

Humidity

Moderate to high

Lifespan

Annual, biennial, or short-lived perennial

Native To

Europe, temperate Asia, North Africa

Toxicity

Skin irritant

Bloom period

Spring – Fall

In flower about 9 months of the year

Planting

How to Grow

Select a site with partial to full shade and well-drained soil, though it tolerates full sun if consistent moisture is provided.
Sow seeds directly onto the soil surface in spring, as they germinate readily without deep burial.
Water moderately to maintain moist soil conditions, especially during dry spells, though established plants tolerate brief dry periods.
Monitor the planting area closely after flowering and hand-pull plants before the seed capsules mature to prevent unwanted spreading.

Pro Tip

Do not mistake this species for a benign woodland wildflower; its schizocarps eject seeds several meters, allowing it to rapidly colonize and displace delicate understory flora if not selectively pulled before seed set.

Keep It Thriving

Care Guide

Do

Grow in well-drained soil to prevent fungal root rot.
Hand-pull plants selectively after flowering to control self-seeding.
Wear gloves when handling the foliage if you have sensitive skin to avoid contact dermatitis.

Don't

Do not apply heavy fertilizer, as excess nutrients promote weak, rank growth.
Do not prune heavily into old, leafless wood.
Do not allow plants to set seed freely near delicate native understory species.

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Pest Check
Plant
Prune
Spring Cleanup

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Rock gardensShaded bordersNaturalized woodland gardens

Companion Plants

Tiarella cordifolia Polystichum acrostichoides Asarum canadense

Multiply

Propagation Methods

Good to Know

Common Questions

Herb-Robert questions

What zones can Herb-Robert grow in?

Herb-Robert is hardy in USDA Zones 4–8. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

Is Herb-Robert deer resistant?

Not reliably. Deer may browse Herb-Robert, especially tender spring growth — plan on repellents or fencing where pressure is high.

When does Herb-Robert bloom?

Herb-Robert typically blooms in spring through fall. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Herb-Robert need full sun?

Herb-Robert does best in full sun to part shade. In hot climates, afternoon shade keeps blooms fresher longer.