How to Grow Clarkia 'Crown Double Mix'
(Mountain Garland) from Seed
The Mountain Garland — long upright spikes packed with double blooms in salmon-pink, royal purple, carmine-red and white that look like miniature ruffled roses threaded along a stem; a Californian native that thrives in British cool summers, direct-sown into poor soil, with ten-day vase life
At first glance, Clarkia Crown Double Mix looks like the work of someone who threaded a string of miniature, ruffled roses along a straight stem and called it a garden plant. The blooms — fully double, with tissue-paper-soft petals arranged in dense, rounded layers — are individually small (2–3cm) but produced in such profusion along the upright stems that the overall effect is of a richly loaded garland. In a mix of salmon-pink, royal purple, crisp white, and carmine-red, the spikes have a richness of colour and a delicacy of texture that genuinely earns the common name Mountain Garland.
Clarkia unguiculata (previously C. elegans) is native to the foothills and mountains of California — open, rocky, sun-drenched terrain with cool nights and seasons of moderate rainfall that map fairly precisely onto a British summer climate. This is why Clarkia is one of the few plants that performs demonstrably better in a UK summer than in many other temperate climates: the British tendency toward cool-warm rather than hot-dry summer conditions is exactly what Clarkia evolved for. It is genuinely well-adapted here, and its reliability in UK growing conditions is exceptional for a plant of such apparently exotic appearance.
Quick Facts at a Glance
Plant Type
Hardy Annual (H3/H4)
Sowing Time
Sep (preferred) · Mar–May direct
Flowering
June–August (from autumn sow); July–Aug (spring)
Height
60–90cm; upright spikes
Soil
Poor, lean, slightly acid — no manure
Difficulty Rating
2 out of 5 — Easy with correct soil
Understanding the Plant
Clarkia unguiculata is a member of the Onagraceae (willowherb) family — related to evening primrose and fireweed. Named after Captain William Clark of the Lewis and Clark Expedition (which botanically documented the American West in 1804–06), Clarkia was brought to European cultivation in the early nineteenth century and became a popular cutting garden annual. The double-flowered Crown Mix produces blooms with significantly more petals than wild-type Clarkia, creating the full, ruffled, rose-like appearance that distinguishes the ornamental form from the simple species.
Direct Sow Only — The Small Root System Rule
Clarkia has a relatively small, delicate root system that is easily damaged by transplanting — unlike many annuals, it does not recover well from root disturbance. Direct sowing into the final growing position is strongly preferred. If indoor sowing is necessary (for an earlier start), use deep biodegradable pots or root trainers that can be planted out intact without disturbing the roots. Standard module trays and pricking out are not recommended for Clarkia — root disturbance almost always causes setback and reduced flowering performance.
Poor Soil and No Manure — The Counterintuitive Rule
Clarkia is one of a small group of plants that actively performs better in lean, slightly acid, unfertilised soil. Adding garden compost, manure, or high-nitrogen fertiliser before sowing produces the opposite of the desired result: lush, leafy, tall, floppy stems with relatively few flowers — the condition known as "lodging" in arable farming. On genuinely poor, slightly acid ground (and Clarkia even tolerates slightly acid, sandy soils where other plants struggle), the plant directs its energy into flower production rather than vegetative growth. If the soil in the sowing area was manured for a previous crop, Clarkia may not perform at its best there — choose a different, less-enriched patch.
Sowing & Establishment
Autumn Sowing (September) for Tallest, Earliest Plants
Clarkia sown in September produces plants that are markedly taller, earlier-flowering, and more productive than the same variety sown in spring. Autumn-sown plants overwinter as small, frost-resistant seedlings, develop a more robust root system, and surge into growth in March — producing stems of 80–90cm by June and flowering from late June onwards. Spring-sown plants (March–May) are reliable but typically shorter (60–70cm) and flower later (July–August). For the most spectacular results, sow in September.
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Direct sow at the final position — cover very lightly or not at all. Clarkia seeds need a small amount of light to germinate — scatter onto finely raked soil and cover with no more than 1–2mm of fine soil or vermiculite. Deeper covering prevents germination. Germination takes 7–14 days. In September, germination is slower (10–21 days) as soil cools.
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Thin to 20cm spacing. Thin when seedlings are 5–7cm tall. Clarkia at correct spacing produces multi-stemmed, upright plants; overcrowded plants produce one central stem with fewer side spikes. Remove surplus seedlings cleanly at soil level rather than pulling — less root disturbance for remaining plants.
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Pinch the growing tip when plants reach 10–12cm. Pinching out the very tip of the main stem when plants are 10–12cm tall encourages the development of multiple side stems rather than a single central spike. The result is a bushier plant with many flowering stems rather than one tall spike — significantly more flower production per plant. This is the most important optional management step for Clarkia.
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No feeding, no manure. Do not add any fertiliser or compost to the sowing position — this is one of the few annuals where feeding actively reduces performance. The lean, slightly acid, well-drained conditions that Clarkia evolved for in the California mountains are the conditions that produce the best UK results.
Growing On & Care
Loves British Summers
Clarkia is genuinely better suited to UK growing conditions than many apparently British flowers — its Californian foothill origin means it is adapted to cool-warm rather than hot-dry summers, exactly what British weather provides. In very hot summers (above 28°C sustained), flowering quality reduces; in the typical British cool-warm summer, Clarkia is at its absolute best.
Cut Flower Champion
Clarkia is one of the finest cut flowers in the annual range — the long, straight stems, the unusual double-flowered rose-like blooms, and the ten-day vase life make it a florist-grade cutting garden essential. Harvest when one to two buds at the bottom of the spike have fully opened; the remaining buds will open progressively in the vase over the following week, giving a changing, evolving arrangement. Strip ALL lower leaves from the stem before placing in water — any foliage below the waterline causes rapid stem decay that dramatically shortens vase life.
Light Watering
Clarkia needs moderate, consistent moisture — not drought-stressed but also not waterlogged. In the lean, well-drained soil that suits it best, water every five to seven days in dry conditions. Overwatering in rich soil produces the leafy, lodging growth that poor soil avoidance is designed to prevent. On genuinely poor, sandy soil, Clarkia may need watering every three to four days in hot weather.
Light Support
The 60–90cm stems of Clarkia can topple in exposed positions or after heavy rain, particularly on richer soil where stems become more lush and top-heavy. Insert pea-sticks (twiggy hazel or willow branches) among the planting when stems reach 30cm. The plants grow up through the sticks naturally and the support becomes invisible. Autumn-sown plants with their stronger root systems require less staking than spring-sown equivalents.
Self-Seeding
Allow some late-season spikes to set seed — Clarkia self-seeds reliably into suitable conditions and the following year's self-seeded plants tend to choose exactly the right position and spacing instinctively, often performing better than deliberately placed plants. The self-seeded colony gradually establishes in the most suitable corner of the garden without any gardener intervention.
The Colour Range
The Crown Double Mix spans from palest salmon-pink through coral, carmine-red and deep crimson to royal purple, lavender, and crisp white — an unusually wide warm-to-cool spectrum within a single annual mix. Individual plants produce one colour per plant, so a group of twelve to fifteen plants scattered across the border creates a naturalistic tapestry rather than a regimented row.
When to Expect Flowers
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| 🍂 Autumn Sow |
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| 🌿 Spring Sow |
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| 🌸 Flowering |
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Common Problems & Solutions
| Problem | Likely Cause | What to Do |
|---|---|---|
| Lush leafy stems, few flowers | Rich soil; recent manure; high nitrogen | Move to a leaner, less-enriched position. Do not add compost or fertiliser before sowing. Rich soil is the single most common cause of disappointment with Clarkia — the plant channels all energy into vegetative growth rather than flowering in nitrogen-rich conditions. Choose the poorest bed in the garden. |
| Plants fall over | Rich soil; insufficient support; heavy rain | Insert pea-sticks when plants reach 30cm. Grow in lean soil — rich soil produces lush stems that cannot support themselves. Autumn-sown plants have stronger stems and better wind resistance than spring-sown. |
| Short vase life (2–3 days) | Lower leaves not stripped; cut too late | Strip ALL foliage from the lower two-thirds of the stem before placing in water — every leaf below the waterline causes rapid bacterial growth that blocks the stem. Cut when one to two bottom buds have just opened. Change water daily. With correct preparation, ten days is achievable. |
| Poor germination | Covered too deeply; wrong sowing time | Cover seeds with no more than 1–2mm of fine soil — deeper covering prevents germination. In September, germination is slower in cooling soil but still reliable. In cold, wet autumn conditions, a light covering of garden fleece over the sowing area until germination speeds the process. |
Plant Specifications
The Mountain Garland — Californian prairie beauty in a British cutting garden
Clarkia Crown Double Mix is one of those plants that consistently surprises — the blooms look too elaborate, too rose-like, too exotic to emerge from seeds scattered on bare ground in September. But that is exactly what happens: sow into lean, unfertilised soil, barely cover, pinch at 12cm, support at 30cm, and by late June the 80–90cm spikes laden with ruffled double flowers in salmon, purple, crimson and white are ready to cut and condition. Strip the lower leaves, arrange in cool water, and discover that the cutting garden plant most worth growing looks like it came from a professional florist's workshop.
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