How to Grow
Lavatera arborea Tree Mallow from Seed
The toughest plant you can grow from seed -- a Hardy Biennial H4 that rises to 2m with a thick woody stem, large velvety ivy-shaped leaves, and hundreds of purplish-pink hibiscus-like flowers from June to September; thrives in salt spray, high winds, poor stony soil, and coastal exposure where other plants fail; indifferent to soil quality; self-seeds for permanent colonies; sow in individual pots from March; one of the most reliable and architecturally dramatic biennials available
Lavatera arborea (now botanically Malva arborea) -- the Tree Mallow -- is the plant that thrives where almost nothing else survives. Native to the windswept cliff-tops and rocky coastal margins of western Europe from Ireland to the Mediterranean, it has evolved over millennia to handle the conditions that defeat most ornamental garden plants: salt-laden air, persistent strong winds, thin poor stony soil, and the drought of exposed rock faces. In a garden context, this evolutionary toughness translates to a plant of extraordinary reliability that tolerates the range of challenging conditions -- exposed corners, poor soils, coastal gardens, north-facing borders -- that most gardeners struggle to fill.
The plant itself is extraordinary in its ambition: a biennial that grows a thick, woody-stemmed structure resembling a small tree reaching up to 2 metres in its second year, clothed in large velvety ivy-shaped leaves of a rich, saturated green, and covered from June to September with hundreds of hibiscus-like flowers in a purplish-pink with the distinctive dark veining that gives each bloom its tropical quality. The combination of architectural size, exotic leaf texture, and abundant flower production makes Tree Mallow the statement plant of a difficult position -- the plant that turns a problem corner into a feature.
Quick Facts at a Glance
Plant Type
Hardy Biennial H4 -- woody-stemmed; behaves as short-lived perennial in mild areas
Flowers
Purplish-pink with dark veins; hibiscus-like; 5cm; June-September; very bee-friendly
Height
Up to 2m in one season; woody-stemmed architectural giant; velvety ivy-shaped leaves
Toughness
Thrives in poor stony soil, salty coastal exposure, high winds -- virtually indestructible
Sow
March-May indoors in individual pots 1cm deep; or direct outdoors late spring
Difficulty
1 out of 5 -- one of the most forgiving plants available from seed
Understanding the Tree Mallow
The Toughest Plant You Can Grow
Lavatera arborea holds a unique position among biennial plants: it has genuinely evolved for the most challenging growing conditions available. The salt-excretion glands in its leaves allow it to grow in direct coastal exposure -- it actually excretes excess salt through the leaf surface, a capability that most plants simply do not possess. The deep, fibrous root system that develops in stony, poor soil provides both the drought tolerance and the structural anchorage to resist persistent high winds. In a sheltered, rich garden border, it grows with equal vigour but without needing any of these adaptations; the same toughness that evolved for cliff-top survival translates to robust, low-maintenance growth in ordinary garden conditions.
Biennial with Perennial Tendencies
Lavatera arborea is technically a biennial -- year one of rosette and woody-stem development, year two of spectacular flowering -- but in the milder coastal regions of the UK (where it is most at home), individual plants often survive for 3-4 years, providing the architectural structure year after year rather than completing the biennial cycle and dying. Even in inland gardens, the prolific self-seeding behaviour means that as individual plants complete their biennial cycle, self-sown offspring are already established to replace them. The distinction between biennial and short-lived perennial is effectively academic in a garden where the plant is allowed to self-seed.
The Botanical Name Change
Lavatera arborea is still widely known and sold under the Lavatera name, but current botanical classification places it in the genus Malva as Malva arborea (also referred to as Malva eriocalyx in some sources). The genus Lavatera has been largely merged into Malva following genetic analysis showing the two genera were not distinct. In the garden, the plant is unchanged by the name revision -- it is the same magnificent woody-stemmed coastal giant it has always been.
Sowing & Growing On
Sow March-May in Individual Deep Pots -- Deep Taproot Develops Early
Sow one seed per individual 9cm deep pot, 1cm deep, indoors from March-May at 15-20°C. Germination in 14-21 days. The plants grow quickly and develop a woody stem and deep root -- pot on to a 1-litre pot when roots emerge from the drainage holes. Do not allow to become pot-bound. Plant out after hardening off when all frost risk has passed.
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Sow indoors March-May in individual deep 9cm pots, 1cm deep, at 15-20°C. One seed per pot. Germination 14-21 days. Or direct sow outdoors in late spring when soil has warmed -- direct sowing often produces stronger plants as the taproot develops undisturbed.
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Pot on to a 1-litre pot when roots emerge from drainage holes. Tree Mallow grows fast -- pot on before the plant becomes pot-bound. Use a free-draining compost. The young plant develops a noticeably woody stem from an early stage.
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Harden off over 10 days; plant out in full sun or light shade, in any soil, after frost. Space 60-90cm apart -- the plant reaches 2m tall and spreads substantially. No soil improvement needed: Tree Mallow thrives in poor, stony, sandy, or clay soils. Rich, heavily amended soil produces excessive leafy growth at the expense of flowers.
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Water well in the first summer; once established, leave to its own devices. Tree Mallow is highly drought-tolerant once its root system is established. After the first summer, supplementary watering is rarely needed except in extended extreme drought. No feeding required.
Growing On & Care
Coastal and Exposed Gardens
Tree Mallow is the go-to plant for the conditions that defeat most ornamental garden plants: high wind exposure, salt spray, poor stony soil, and coastal desiccation. In these conditions, where even hardy perennials struggle, Lavatera arborea grows with uninhibited vigour, providing the architectural height, dense foliage cover, and abundant flower production that makes a challenging position into a genuine garden feature. For coastal gardeners who struggle to find anything that will survive, this is one of the very few large-scale flowering plants that genuinely thrives rather than merely tolerating exposure.
Architectural Statement
At 2 metres with a thick, woody stem and large velvety leaves, Tree Mallow creates the kind of exotic, lush structural presence in a border that is more typical of tropical conservatory plants than UK biennials. Against a wall or fence in a sheltered garden, a group of three or five Tree Mallows creates a dramatic backdrop that provides height, screening, and flower simultaneously from June through September. The combination of architectural scale and abundant flowering makes it ideal as the back-of-border structural element in any large garden scheme.
Bee Magnet
The large, open, hibiscus-like flowers of Lavatera arborea are highly accessible to bumblebees and honeybees throughout the long June-September flowering season. The flowers are visited almost continuously by bees in warm weather, making Tree Mallow one of the most effective large bee-support plants available from seed. In a garden designed with pollinators in mind, a flowering Tree Mallow is a significant resource during the high-summer period when intensive bee foraging coincides with colony peak.
Self-Seeding for Perpetual Colonies
Tree Mallow seeds prolifically. Allow some flower heads to ripen fully in autumn -- the seed pods split and scatter into surrounding soil, producing self-sown seedlings that appear the following spring. These self-sown plants typically establish more robustly than deliberately raised seedlings, particularly in poor or stony soil where the taproot can develop undisturbed. A single well-established Tree Mallow colony self-perpetuates indefinitely, shifting slightly in position with each generation but always maintaining its presence in the garden.
Velvety Leaves as Feature
The large, soft, velvety leaves of Tree Mallow are attractive in their own right -- lobed like a large ivy leaf, deep green, and covered in fine downy hairs that give a distinctly tactile quality. Even before flowering begins in June, a first-year Tree Mallow plant provides substantial leafy structure that fills a border with rich green texture. The leaf texture and scale contrasts particularly effectively with fine-leaved or grass-like companions: Hordeum jubatum (the fine silky grass plumes against the large velvety mallow leaves), or Ammi majus (the lacy white umbels against the bold mallow structure).
Staking in Exposed Positions
Tree Mallow's woody stem is strong, but in very exposed, gale-force wind conditions, the tall 2m plants can rock and occasionally topple. In the most exposed coastal positions, a sturdy bamboo cane inserted alongside each plant provides the necessary insurance against extreme wind events. In sheltered inland gardens, staking is rarely needed -- the woody stem and deep taproot provide adequate anchorage in all but exceptional storm conditions.
Biennial Cycle Calendar
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| Direct sow (late spring) |
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| Plant out (May-Jun) |
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| Overwinters (yr 1 rosette) |
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| Flowers (Jun-Sep yr 2) |
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Common Problems & Solutions
| Problem | Likely Cause | What to Do |
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| Poor germination | Temperature too low; seeds too deep | Germination at 15-20°C in 14-21 days. Seeds buried too deep may fail to germinate -- sow 1cm deep. Alternatively, direct sow in late spring when soil has warmed; direct-sown plants are often more vigorous than pot-raised ones. |
| Plant toppling in wind | Exposed position; no staking | In very exposed, gale-force wind positions, stake each plant with a sturdy bamboo cane. In most garden conditions (sheltered coastal or inland), the woody stem and taproot provide adequate anchorage. |
| Excessive foliage, few flowers | Over-rich soil; too much feeding | Tree Mallow thrives in poor, lean soil. Rich, heavily fertilised conditions produce excessive leafy growth at the expense of flower production. Grow in unimproved or lightly improved soil without supplementary feeding. |
| Plant dies after flowering | Normal biennial behaviour | Lavatera arborea is a biennial -- individual plants complete their life cycle and die after flowering. The self-seeding habit means new plants appear to replace them. In mild coastal gardens, individual plants sometimes survive for 3-4 years as short-lived perennials. |
Plant Specifications
The 2-metre coastal giant that thrives on neglect -- hibiscus flowers from June to September in the most challenging position you have
Sow in individual deep pots at 15-20°C from March to May. Plant out in full sun in any soil after frost -- no soil improvement needed. Water well in the first summer. Then leave it alone. The thick woody-stemmed giant rises to 2m in year two, covered in purplish-pink hibiscus flowers that bees visit continuously from June to September. Allow some seed pods to ripen for a permanent self-renewing colony.
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