Hollyhock

Alcea rosea

The Gardening Year

Best months in UK gardens · full planting calendar →

At a Glance

Overview

Hollyhock (Alcea rosea) is a tall, old-fashioned cottage-garden favourite grown for its towering spikes of large, showy flowers in summer. The following quick-care table summarises the essentials for UK growers; the full article below covers each in detail.

Hollyhock (Alcea rosea) is an erect herbaceous plant in the family Malvaceae, closely related to mallow, marshmallow and tree mallow. It is most often treated in British gardens as a biennial, producing a low rosette of leaves in its first year and a tall flowering spike in its second, although in mild districts and on free-draining soil it can persist as a short-lived perennial for several seasons. Native originally to south-west Asia, it has been grown in British cottage gardens since at least the sixteenth century and remains one of the most recognisable of vertical summer plants. The flowering spikes typically reach 1.5 to 2.5 m, much taller than almost any other commonly grown border perennial, and they carry a long succession of large, open, often disc-shaped flowers from midsummer well into early autumn. Colours in the species and its old cultivars range through pink, rose, crimson, purple, yellow and white. Hollyhocks are widely used at the back of herbaceous borders, against sunny walls and fences, and in informal drifts to give height, and they are a reliable nectar source for bumblebees, honeybees and hoverflies during the height of summer. They self-seed readily, and a well-established colony tends to maintain itself year after year even though individual plants may be short-lived.

Appearance

Alcea rosea forms a clump of large, rounded to broadly heart-shaped leaves at the base, each typically 10 to 25 cm across, shallowly lobed with a softly crinkled, slightly hairy surface. From this basal rosette rise one to several stout, erect, unbranched flowering stems clothed in smaller, alternately arranged leaves that diminish in size up the stem. The whole plant has a characteristically rough, hairy texture, and the stems are tough and fibrous rather than woody. The flowers are borne in the leaf axils along the upper portion of the spike, opening progressively from the bottom upwards over a period of several weeks. Each flower is 5 to 10 cm across, with five broad, overlapping petals arranged around a central column of fused stamens typical of the mallow family. Both single and double forms exist: singles have a flat, open face that displays the central boss of stamens, while doubles carry many extra petals and tend to look more like a peony or a small rose. The colour range in old seed-raised strains covers pink, rose, red, crimson, purple, almost black-red, yellow, cream and white, often with a paler or darker centre. After pollination the flowers develop the characteristic flat, disc-shaped seed heads of the Malvaceae, each packed with numerous wedge-shaped seeds. Once flowering finishes, the dead spikes can be left standing both for their structural value and for seed harvest.

Growing Conditions

Hollyhocks grow best in full sun, in well-drained, moderately fertile soil with a pH in the near-neutral to slightly alkaline range, roughly 6.0 to 7.5. They are deep-rooted and tolerate drier conditions than their soft, hairy leaves might suggest, but they resent winter wet, and on heavy or compacted clay the crowns are prone to rot. Where drainage is poor, planting on a slightly raised bed, at the top of a wall, or against a sunny wall where the soil dries out quickly between rains is far more reliable. They flower most freely in a warm, sheltered spot — a south- or west-facing aspect against a wall is ideal — although they will tolerate light afternoon shade. Strong winds are the main physical hazard: the tall, top-heavy spikes catch the wind and snap easily, so a sheltered site or some form of support is wise. Hollyhocks are hardy across most of the UK in well-drained soil; the plant badge carries the precise RHS hardiness rating. They dislike being moved once established, so it pays to choose the planting position carefully from the outset. They are also tolerant of coastal exposure and of the dry, reflective conditions found against warm house walls.

Planting and Care

Plant container-grown hollyhocks in spring (March to May) or in early autumn (September), spacing them 45 to 60 cm apart to allow good air movement between the tall spikes and to accommodate their mature spread. In their first season, water regularly during dry spells to help the young plants establish a deep root system; once established, additional watering is rarely needed except in prolonged drought. Feeding should be modest: a single application of a balanced general-purpose fertiliser in early spring, followed by a potassium-rich liquid feed (such as a tomato feed) every fortnight from early July until late August, supports strong flowering without producing over-lush foliage that is more susceptible to rust. The single most useful piece of routine care is deadheading: as each flower fades, pinch it off, and once the whole spike has finished, cut it back to a strong side-shoot or to the basal rosette. Leaving a few spikes to set seed will keep the colony going, as hollyhocks self-seed prolifically and the offspring usually come true to type in old cottage-garden strains. In autumn, after flowering has finished and the foliage has died back, cut the spent stems down to within a few centimetres of the ground and clear away any debris to reduce overwintering rust spores. A light mulch of garden compost around the crown in late autumn helps protect it through winter; avoid heavy mulches that sit wet against the stems. Divide established clumps in autumn or in early spring as the new growth emerges, lifting the entire rootstock and splitting it with a sharp spade; replant the younger, outer sections and discard the woody centre. Propagation is straightforward from seed sown in spring or in late summer: surface-sow on a gritty, free-draining compost, keep it just moist, and pot on the seedlings once they have two true leaves. Hollyhocks also grow readily from basal cuttings taken in spring.

Common Problems

Hollyhock rust (Puccinia malvacearum) is by a wide margin the most damaging disease of Alcea rosea in the UK. It appears first as small yellow-orange pustules on the undersides of the lower leaves, with corresponding pale spots on the upper surface, and it spreads rapidly up the plant in warm, humid weather, causing leaves to yellow and fall prematurely and leaving the spikes looking stripped and unsightly by late summer. The fungus overwinters on plant debris and on neighbouring mallows, so end-of-season hygiene — cutting down and destroying affected stems, clearing leaf litter from around the base, and avoiding dense planting — is the single most effective control. Where rust has been a problem in previous years, spraying with a suitable fungicide at the first sign of infection can slow its spread, but the long-term answer is usually a combination of good air circulation, clean cultivation and the gradual replacement of susceptible plants with more resistant seed strains. Powdery mildew can affect hollyhocks in late summer under dry, still conditions, coating the leaves in a white, dusty layer; it is less damaging than rust and is largely cosmetic. Slugs and snails can be troublesome on young seedlings and on the soft new spring growth. Leaf spots caused by various fungi may appear in wet seasons but are usually of minor importance. The hollyhock weevil (Apion longirostre), a small dark weevil whose larvae bore into the stems and roots, is recorded in the UK and can weaken individual plants; hand-removal of adults and the destruction of infested stems help to keep numbers down. Hollyhocks are not considered toxic to humans or to domestic animals.

Popular Varieties

'Alcea rosea' is most often grown from mixed cottage-garden seed strains, which throw the full colour range of pinks, reds, whites, yellows and purples in a single sowing and self-seed freely thereafter. Single-flowered mixed strains are the most graceful and the most attractive to pollinators; doubles, such as the old 'Chater's Double' group, produce densely petalled, peony-like flowers in a wide colour range and are useful where a more solid mass of colour is wanted, although they set less seed than singles. 'Nigra' is a venerable single form prized for its very dark, almost black-maroon flowers, which read as deep red at a distance and contrast strongly with paler pinks and whites. The Halo Series carries single flowers in mixed colours, each with a contrasting paler or darker centre, and is widely available as seed. For smaller gardens, shorter strains such as 'Majorette' reach only about 75 cm and need neither staking nor the space of full-height forms, while 'Spring Celebrities' is a compact double strain of similar height useful for the front of a border or for containers. White-flowered forms, sold variously as 'Alba' or under white-mix labels, are particularly effective against dark fences and evergreens and combine well with old roses and the silver foliage of artemisias in a traditional cottage planting.

Pests and Diseases

For step-by-step help, read Controlling Aphids Naturally and Dealing with Slugs and Snails. Or browse the full plant problem solver to diagnose an issue by symptom.