Herb Robert
Also known as
Robert geranium, Red Robin, Stinking Bob, St. Robert's herb, Herb-Robert
Keep this plant’s care guide close at hand.
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Geranium robertianum, commonly known as Herb Robert, is a delicate annual or biennial cranesbill native to Europe, western Asia, and North Africa, and widely naturalized elsewhere. It typically grows 10–50 cm tall with slender, reddish, branching stems and finely divided, ferny leaves that emit a strong musky aroma when crushed. Leaves often redden in cool weather or strong light. From spring to autumn it bears small, five-petaled, bright pink flowers (about 1–1.5 cm across) that are followed by the characteristic beaked seed capsules of cranesbills. The seeds are dispersed by an elastic, catapult-like mechanism. Herb Robert thrives in semi-shade and lean, well-drained soils, commonly colonizing woodland edges, hedgebanks, rocky crevices, old walls, and other disturbed, base-rich sites. It is a quick grower and prolific self-seeder, sometimes behaving like a benign garden weed. Ecologically, it supports small bees, hoverflies, and other pollinators. Historically, it has been used as an astringent herb in folk medicine, though it is primarily valued today for its shade tolerance and naturalizing habit.
Taxonomy
Properties & Requirements
How to care for Herb Robert
Water
Keep seedlings evenly moist until established. Thereafter, Herb Robert tolerates dry shade and prefers the soil to dry slightly between waterings. In pots, water thoroughly, then wait until the top 2–3 cm of mix is dry before watering again. Always use a free-draining medium and containers with drainage holes. Avoid prolonged saturation, which can cause root issues, yet don’t allow extreme drought during flowering if you want continuous bloom.
Light
Best in partial shade to full shade with bright, indirect light. Morning sun is generally fine, but intense midday sun can scorch foliage, especially in warmer regions or dry sites. In cool, maritime climates it tolerates more sun if soil moisture is adequate. In deep shade it will still flower, though plants may be leggier. Foliage often reddens under high light or cool temperatures, a normal, non-harmful response.
Nutrients
Herb Robert is adapted to nutrient-poor, often calcareous sites and needs little to no fertilizer. Overfeeding encourages lush, floppy growth and reduces flowering. In containers, mix a small amount of mature compost into a gritty, well-draining medium and, if needed, apply a very dilute balanced fertilizer (e.g., 5-5-5 at quarter strength) once monthly during active growth. Avoid high-nitrogen products and do not fertilize in winter or during heat-induced dormancy.
Temperature
Optimal growth occurs in cool to mild conditions (about 10–24°C). The plant tolerates frost and light to moderate freezes, often overwintering as a reddish rosette, while seeds readily survive winter. Prolonged heat above ~30–32°C may cause plants to stall or die back; provide shade and consistent, light moisture during heat waves. Container-grown plants should be protected from severe, prolonged hard freezes, especially if the rootball could freeze solid.
