Bigroot Geranium: expert tips for growing this hardy ground cover

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Geranium macrorrhizum is one of the most dependable ground-cover perennials in cultivation, forming a dense carpet of rounded, aromatic leaves topped with clouds of pink or white flowers in early summer. It thrives in the difficult places most plants refuse — dry shade beneath trees, steep banks, gaps in walls — and needs almost no attention once settled. Crush a leaf between your fingers and you will find the distinctive resinous, slightly balsamic scent that gives it the name big-root cranesbill.

Growing conditions

Few perennials are as adaptable to light levels. Geranium macrorrhizum flowers most freely in full sun or dappled light, but it will still knit together happily in full shade beneath deciduous trees and large shrubs. In hot climates, afternoon shade keeps the foliage fresher and greener through midsummer.

Soil requirements are minimal, provided drainage is reasonable. It tolerates thin, stony, chalky and sandy soils that defeat other geraniums, and copes with a pH from mildly acidic to distinctly alkaline. The one condition it dislikes is heavy, waterlogged clay in winter, where the thick fleshy rhizomes may rot.

Native to the mountains of southern Europe, this species is exceptionally cold-hardy and shrugs off wind, frost and dry root competition. Gardeners in Mediterranean or continental climates will find it one of the most reliable ground covers for unirrigated shade.

How to plant Geranium

Plant in early autumn or early spring, when the soil is warm and moist enough for the rhizomes to root away quickly. Autumn planting is best in dry regions, giving the plant a full winter of establishment before summer heat arrives.

• Spacing: set plants 40–45 cm apart for cover within two seasons, or 30 cm apart if you want a closed carpet by the following summer.
• Depth: the thick surface rhizome should sit level with the soil, never buried — covering the crown encourages rot.
• Soil preparation: loosen compacted ground and fork in a little leaf mould or garden compost; avoid rich manures, which soften growth.
• Watering in: soak thoroughly after planting and water weekly for the first six to eight weeks, especially under trees where the soil is dry.
• Propagation: snap off a 10 cm length of rhizome with a few leaves attached, press it onto moist compost and it will root within a month — no special equipment needed.

Care through the seasons

Spring: Tidy away any leaves that have blackened or flattened over winter to let fresh growth through cleanly. A light mulch of leaf mould around, not over, the crowns is all the feeding required. Plants in poor soil appreciate a scattering of general-purpose organic fertiliser as growth begins.

Summer: Established clumps rarely need watering, though new plants benefit from a soak in prolonged drought. Once the main flush of flowers fades in July, shear the whole plant back by roughly half with hedging shears; this removes tired foliage and often triggers a second, lighter flowering. Trim any spreading rhizomes that creep over paths or into smaller neighbours.

Autumn: This is the ideal time to divide congested colonies — simply pull or cut apart the rhizomes and replant immediately. Leave the foliage in place, as it protects the soil and often colours attractively in shades of red, bronze and amber. Top-dress hungry, dry sites with compost.

Winter: The plant is semi-evergreen and usually holds a low mat of leaves all winter, needing no protection whatsoever. In very severe cold the foliage may collapse and brown, but the rhizomes resprout reliably in spring.

Best varieties to grow

Several long-established cultivars offer better flower colour and neater habit than the wild form.

• ‘Ingwersen’s Variety’ — soft lilac-pink flowers, pale green glossy foliage and a particularly good garden habit; holds an RHS Award of Garden Merit.
• ‘Bevan’s Variety’ — the boldest colour, with deep magenta-pink petals and conspicuous red calyces; excellent for lifting shady corners.
• ‘Album’ — white flowers flushed pink at the base with pink sepals, the most refined choice for a woodland or white scheme.
• ‘Spessart’ — pale pink to nearly white flowers and foliage that turns outstanding russet-red tints in autumn.

Pests, diseases and common problems

• Crown and rhizome rot: plants collapse and turn mushy at the base in wet, heavy soils. Improve drainage with grit before planting, keep rhizomes at surface level and avoid mulching directly over crowns.
• Powdery mildew: a white bloom on leaves in hot, dry summers, particularly in poor air circulation. Shear the plant back hard, remove affected leaves and water at soil level rather than overhead.
• Vine weevil: mainly a problem in containers, where cream grubs eat the roots and cause sudden wilting. Repot into fresh compost, remove grubs by hand and apply a biological nematode drench in late summer.