How to Grow Malva
'Mystic Merlin' from Seed
The towering tapestry of purple, mauve, and elusive blue -- a Short-lived Perennial H5 reaching 1.5-1.8m in its first year from seed, producing 5cm saucer-shaped flowers with darker vein flames in the rarest cottage garden colour range from June to October; exceptionally unfussy about soil; RHS Plants for Pollinators; edible flowers for spectacular salad garnish; cut back by half in July for a second full flush; prolific self-seeder for permanent colonies
Malva sylvestris 'Mystic Merlin' earns its name from the colour that makes it remarkable: the "elusive blue" that appears among the rich purples and mauves of the flower mix is one of the very few genuinely blue flowers available in a cottage garden perennial of this height and habit. Most so-called blue garden flowers are, in reality, purple or violet; the true blue that appears in Mystic Merlin -- influenced by the light conditions and individual plant genetics -- is a genuine, saturated blue that garden designers spend considerable effort trying to source. Combined with the dramatic darker vein "flames" that plunge toward the flower centre and the impressive 1.5-1.8 metre height of the plant, this colour quality makes Mystic Merlin one of the most sought-after back-of-border plants available from direct seed sowing.
The practical virtues match the visual ones. Mystic Merlin is exceptionally unfussy about soil -- it grows happily in everything from heavy clay to dry, sandy ground, provided reasonable drainage is maintained. It flowers from June through to October in its first year from an early spring indoor sowing, giving the same season-long display that most perennials only achieve in their second or third year. It is a prolific self-seeder, dropping seeds that establish new plants around its base and providing a permanent, free-renewing colony once the first generation has established. And the flowers and leaves are fully edible -- the deep purple flowers providing an extraordinarily striking garnish for summer salads, desserts, and botanical cakes.
Quick Facts at a Glance
Plant Type
Short-lived Perennial H5 -- flowers year one from Feb sowing; 3-4 years lifespan
Flowers
Rich purple through mauve to rare elusive blue; darker vein flames; 5cm; Jun-Oct
Height
1.5-1.8m tall; towering back-of-border statement; first-year flowering
Colour
One of the very few plants offering true blue alongside purple in a cottage garden
Edible
Flowers and young leaves 100% edible; spectacular salad garnish; botanical cakes
Difficulty
1 out of 5 -- any soil, minimal care, towering drama from seed
Understanding the Plant
The Elusive Blue -- Why It Is So Rare
True blue in garden flowers results from specific anthocyanin pigments (most commonly delphinidin) combined with particular pH conditions within the flower cell vacuole. Most blue-appearing flowers are actually purple-shifted, with the blue wavelengths partially suppressed by co-pigmentation with reddish anthocyanins. In Mystic Merlin, the genetics of certain individual plants produce the specific delphinidin-dominant pigmentation that results in genuine clear blue flowers -- and the exact shade varies between plants and even on the same plant under different light and temperature conditions. This variability is part of the variety's character: the "ever-changing tapestry" quality that makes it uniquely interesting to observe throughout the season.
Height and Back-of-Border Impact
At 1.5-1.8m from an early indoor sowing in the first year, Mystic Merlin provides genuine back-of-border height comparable to a well-grown Delphinium or Hollyhock but from a short-lived perennial that is significantly more adaptable in its soil requirements than either. The tall, leafy stems carrying clusters of saucer-shaped flowers in their leaf axils create a dense, architectural presence that provides structure and colour simultaneously from June through October. In a long border, a group of 3-5 Mystic Merlin plants provides the back-row statement that anchors the entire planting composition.
The Mid-Summer Chop
As with all Malva sylvestris varieties, Mystic Merlin can look somewhat leggy and tired after its first intense flowering flush in June-July. Cutting the stems back by approximately half at this point -- a bold action that feels alarming but is entirely appropriate -- stimulates vigorous lateral branching and a second, full flush of flowering in August through October that matches or exceeds the first. The chop also prevents the plant from exhausting itself too quickly, extending individual plant longevity. Water well immediately after cutting back.
Sowing & Growing On
Sow Indoors Feb-May at 15-20°C -- Transplant Carefully at 60cm Spacing -- Back of Border
Surface sow or cover lightly with vermiculite at 15-20°C indoors Feb-May. Germination 14-21 days. Transplant carefully to individual pots; transplant again to final position at 60cm spacing after hardening off. Back of border, full sun or partial shade, any reasonably drained soil.
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Sow indoors Feb-May at 15-20°C, surface sowing or covering lightly with vermiculite. Germination 14-21 days. Alternatively, direct sow outdoors in May when soil has warmed. Handle seedlings carefully at all stages -- Malva dislikes root disturbance and transplants best at the smallest size practical.
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Pot on into individual 1-litre pots when large enough to handle. Grow on in cool, bright conditions. Do not pot on more than once before final planting out. Harden off over 10-14 days before planting out.
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Plant out at 60cm spacing in full sun or partial shade, in any reasonably drained soil. Back of a border or against a sunny wall for wind shelter -- at 1.5-1.8m, the tall stems can rock in exposed positions. Do not plant in excessively rich soil (produces lush soft growth). No supplementary feeding required.
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Cut back by half after the first flush in July for a second full flowering in August-October. Water well immediately after cutting. The plant regrows vigorously. Allow some seed heads to ripen at the end of the season for the self-seeding colony that will perpetuate the planting permanently.
Growing On & Care
The Colour Tapestry
The term "ever-changing tapestry of rich cool colour" captures something specific about Mystic Merlin: the colour of individual flowers within the same plant, and between plants in a group, shifts across a range from deep royal purple through various intermediate mauves and violets to the occasional genuine blue -- and these colours also shift as the flower ages, with newly-opened flowers often darker and older flowers lighter. A group of five Mystic Merlin plants in flower together simultaneously presents this entire range, creating a cooler-palette tapestry effect that is genuinely complex and interesting to observe rather than simply a block of single colour.
Edible Flowers -- Culinary Value
The deep purple to violet-blue flowers of Mystic Merlin are among the most visually striking edible flowers available from a UK cottage garden. Scattered over a salad, the 5cm saucer-shaped flowers provide extraordinary colour contrast -- the purple-blue against green leaves and yellow or orange dressings creating a plate that looks professionally styled. On a white-iced botanical cake, the flowers are particularly striking. The flavour is mild and slightly mucilaginous (as all mallows), making them suitable as pure garnishes that do not overpower the dish. The young leaves can be added to summer salads for mild green flavour or cooked as a spinach substitute.
RHS Pollinators -- All Season Value
Listed on the RHS Plants for Pollinators list, Mystic Merlin's long June-October flowering season provides a particularly valuable extended nectar and pollen resource. The wide, open saucer-shaped flowers are highly accessible to bumblebees, honeybees, solitary bees, and hoverflies throughout the summer and into early autumn. The October flowering, when many other pollinator plants have finished, is especially significant -- providing critical late-season resources for queens building winter fat reserves and for any late-flying solitary bee species.
Any Soil -- The Clay Tolerance Advantage
Mystic Merlin's tolerance of heavy clay soil is a practical benefit that few tall, dramatically-flowering perennials share. Most back-of-border perennials of similar height (Delphiniums, Lupins, tall Verbascum) struggle or fail in the heavy clay soils common across much of the UK. Mystic Merlin grows enthusiastically in clay, provided there is reasonable surface drainage. For UK gardeners dealing with clay soils who want genuine height and blue-purple flower drama in the back of a border, Mystic Merlin is one of the very few options that delivers reliably.
Self-Seeding Colony
Mystic Merlin is a prolific self-seeder -- allowing seed heads to ripen and shed in late autumn establishes a self-sustaining colony that provides permanent free plants around and near the parent. Self-sown seedlings vary in colour (as the parent plant does) -- the range of purple, mauve, violet, and blue appearing in different proportions in different seedlings. Deadheading to prevent self-seeding is rarely necessary or desirable; the colony management is simply a matter of removing seedlings from positions where they are not wanted while they are still small.
Staking in Exposed Positions
At 1.5-1.8m, Mystic Merlin's tall stems can flex and lean in exposed or windy positions, particularly if grown in rich soil that has produced lush soft growth. In sheltered borders or those with neighbouring plants providing mutual support, staking is rarely needed. In exposed positions, install a single sturdy cane per plant in May when the plant reaches 60-80cm, tying the main stem loosely. The plant's naturally woody, sturdy base provides good anchorage; it is the upper soft stem that benefits from support in exposed conditions.
Sowing & Flowering Calendar
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| Sow (Feb-May indoor) |
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| Plant out (May-Jun) |
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| First flush (Jun-Jul) |
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| Chop; second flush (Aug-Oct) |
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Common Problems & Solutions
| Problem | Likely Cause | What to Do |
|---|---|---|
| Stems leaning or falling | Exposed position; over-rich soil; no staking | Stake individual plants with a sturdy cane in exposed positions. Grow in ordinary, not excessively rich, soil for most compact sturdy growth. Plant 60cm apart to allow adequate light and air around each stem. |
| Rust spots on leaves | Fungal disease in wet conditions | Remove affected leaves promptly. Ensure adequate spacing. Rust is primarily cosmetic in Malva sylvestris and rarely affects flowering quality significantly. Cut back affected plants hard; they regrow cleanly. |
| No blue flowers -- only purple/mauve | Colour varies by individual plant and conditions | Blue flowers are more likely in certain individual plants and in certain light and temperature conditions. The range of purple to blue is a characteristic of the variety, not a problem. Retain the most blue-flowered plants for self-seeding to gradually select for bluer progeny. |
| Plant exhausted after first year | Not cut back in mid-summer; very short-lived form | Cut back by half after the first flush to extend plant life and encourage a second flush. Mystic Merlin lives 3-4 years but can exhaust itself if not cut back. Self-sown replacements are always available if individual plants die. |
Plant Specifications
The elusive blue and deep purple that tower to 1.8m from June to October in any soil -- the most dramatic back-of-border plant from a single seed sowing
Sow indoors Feb-May at 15-20°C. Plant at 60cm spacing at the back of any border with reasonable drainage. Watch the 1.5-1.8m stems rise with their purple, mauve and occasional elusive-blue flowers from June. Cut back by half in July for a full second flush through October. Allow some seeds to ripen for a permanent self-seeding colony.
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