I. Plant Overview

Evening Primrose is a versatile plant combining ornamental, medicinal, and economic value. It features an upright, graceful habit (60-150 cm tall) with sturdy stems and elongated emerald leaves. Its distinctive funnel-shaped flowers—typically golden yellow, with some pink or white cultivars—bloom at night and emit a delicate fragrance, closing by morning. Exceptionally adaptable, it tolerates cold, drought, and poor soil, thriving in gardens, borders, and pots alike. As an important nectar source and medicinal crop, it offers comprehensive value, making it a top choice for horticultural and commercial cultivation.

II. Morphological Characteristics

Evening Primrose has a tall, upright growth habit with lush foliage, balancing ornamental appeal and practicality:

• Stem: Erect, 60-150 cm tall, robust and cylindrical, covered with fine white hairs, green or pale purple. Moderate branching, primarily in the upper portion.
• Leaves: Alternate, lanceolate or oblong-lanceolate, 5-15 cm long and 1-3 cm wide, with sparse serrated margins. Glossy green upper surfaces and downy white undersides, cuneate base, acuminate apex, and short or nearly absent petioles.
• Flowers: Solitary at stem apices or leaf axils, arranged in racemes. Calyx 4-lobed, lanceolate, green and pubescent; 4 obovate petals with distinct veins, mostly golden yellow (some pink/white cultivars), 5-8 cm in diameter. 8 white stamens with yellow anthers; 1 pistil with 4-lobed stigma. Flowers bloom at night, close in the morning, and release a faint fragrance.
• Fruit: Capsule, elongated cylindrical and slightly curved, 2-5 cm long and 0.8-1.2 cm in diameter, brown when mature, dehiscing at the top into 4 parts. Contains numerous small seeds—kidney-shaped, black or dark brown with fine textures, 1000-seed weight 0.3-0.5 grams, germination rate lasts 3-5 years.

III. Growth Habits

Evening Primrose is a sun-loving, cold-tolerant, drought-tolerant, and poor-soil-tolerant plant, preferring warm dry climates and avoiding high temperature, high humidity, and waterlogging:

• Temperature: Optimal growth temperature 15-28℃; seed germination requires 10-20℃ (best at 15-18℃). Extremely cold-hardy—tolerates temperatures below -20℃, with seedlings and mature plants overwintering outdoors in northern regions. Moderate heat tolerance: growth slows above 35℃ in summer; provide shade to prevent leaf yellowing.
• Light: Absolutely sun-loving, requiring 6-8 hours of direct sunlight daily. Sufficient light promotes sturdy stems, abundant blooms, and vibrant colors; insufficient light causes leggy growth, weak stems, sparse flowering, delayed blooming, or no flowering.
• Soil: Undemanding, preferring loose, well-drained neutral to slightly alkaline soil (pH 6.5-7.8), ideally sandy loam or humus loam. Exceptionally tolerant of poor soil, growing in sandy areas and slopes, but intolerant of heavy, waterlogged soil. Compacted or waterlogged soil easily leads to root rot and death.
• Water: Excellent drought tolerance, intolerant of waterlogging. Follow the principle of “water only when dry, water thoroughly when watering”—slightly dry soil is optimal. Keep soil slightly moist during seedling stage to promote root development; strictly control water for mature plants. Appropriately increase watering frequency in hot summer but avoid waterlogging; nearly stop watering in winter, keeping soil dry for frost protection.
• Special Characteristics: Fast growth rate—biennial plants bloom the second year after sowing; well-developed taproot (1-2 meters deep) with few lateral roots, enhancing drought resistance; night-blooming, serving as a key nectar source for nocturnal insects (moths, bats); high seed oil content rich in γ-linolenic acid, offering significant medicinal value; resistant to harmful gases (sulfur dioxide, hydrogen fluoride), suitable for urban greening.

IV. Core Values

1. Ornamental Value: Night-Blooming Charm, Unique Landscape

With an upright habit, vibrant colors, and distinctive flowers, Evening Primrose stands out as a rare night-blooming ornamental. Its golden blooms open at dusk, releasing a delicate fragrance that creates an enchanting atmosphere. Ideal for garden clumps, border backgrounds, or balcony pots, it offers a unique visual experience. Boasting a long flowering season (summer to autumn) and abundant blooms, its golden flowers shine brightly against emerald foliage, delivering exceptional ornamental value.

2. Medicinal & Economic Value: Versatile and Beneficial

Evening Primrose seeds are a valuable medicinal raw material, containing 20%-30% oil rich in γ-linolenic acid and linoleic acid. These unsaturated fatty acids support endocrine regulation, blood circulation improvement, dysmenorrhea relief, and blood lipid reduction, making them ideal for health supplements, pharmaceuticals, and cosmetics. The entire plant is medicinal, clearing heat, detoxifying, reducing swelling, and relieving pain—effective for colds, sore throats, and skin ulcers. Flowers yield essential oils for perfumes and aromatherapy, while the plant serves as a high-quality nectar source, producing abundant, high-quality honey with beekeeping economic value.

3. Ecological Value: Air Purification & Soil Conservation

Evening Primrose exhibits strong resistance and adsorption capacity for harmful gases (sulfur dioxide, hydrogen fluoride), improving air quality in gardens, parks, and urban green belts. Its deep taproot and lateral root spread enhance soil stabilization, making it ideal for slope and wasteland greening to prevent erosion. As a night-blooming plant, it provides critical nectar and habitat for nocturnal insects (moths, bats), fostering ecological balance.

V. Scientific Cultivation Guide

1. Planting Time Selection: Spring & Autumn Sowing

As a biennial herb, Evening Primrose thrives when sown in spring or autumn—autumn sowing is preferred to ensure vigorous vegetative growth and abundant flowering the following year:

• Autumn Planting: Southern regions (Yangtze River Basin and south) can sow in September-October; northern regions in August-September. Mild temperatures and sufficient light promote high germination rates and robust seedling growth, allowing safe overwintering outdoors and flowering in June-July the next year.
• Spring Planting: Southern regions can sow in March-April; northern regions in April-May. Spring-sown plants focus on vegetative growth in the first year, with some vigorous individuals flowering sparingly in autumn—most bloom abundantly the following year.
• Seedling Cultivation: For seedling transplantation, start indoors in February-March (temperature 15-18℃), transplant when seedlings have 4-6 true leaves (April-May). Transplanting accelerates flowering and improves survival rates.

2. Soil Preparation: Loose & Well-Drained

Evening Primrose adapts to various soils, but well-prepared soil enhances growth, flowering, and seed yield:

1. Soil Ratio: Recommended formula: 4 parts garden soil + 2 parts leaf mold + 3 parts river sand + 1 part perlite. Mix well and expose to sun for 3-5 days to disinfect, killing insect eggs and pathogens.
2. Soil Improvement: For heavy clay soil, increase river sand/perlite ratio to improve drainage; for acidic soil, add wood ash or quicklime to adjust pH to 6.5-7.8; for poor soil, mix in decomposed organic fertilizer or compound fertilizer to enhance fertility.
3. Base Fertilizer Application: Mix decomposed organic fertilizer (15-20 kg per mu) or compound fertilizer into soil before planting, ensuring full mixing to avoid root burn. For potted plants, place ceramsite or gravel at the bottom to enhance drainage.

3. Planting Methods: Sowing为主, Seedling Transplantation为辅

Evening Primrose is primarily propagated by sowing—simple and high-success, suitable for large-scale and home cultivation:

1. Sowing Propagation: Soak seeds in 30℃ warm water for 6-8 hours, dry and evenly spread on seedling medium or planting beds, cover with 0.5-1 cm thin soil, and gently compact. Keep moist at 15-18℃; seedlings emerge in 10-15 days. Thin seedlings at 2-3 true leaves (spacing 10-15 cm); transplant at 4-6 true leaves (1 plant per pot/hole, spacing 30-40 cm, row spacing 40-50 cm).
2. Seedling Transplantation: Use seedling trays or pots filled with loose medium. Sow soaked seeds individually, cover with thin soil, and keep moist. Strengthen light and water management after germination; transplant with soil balls when seedlings have 4-6 true leaves to avoid root damage and improve survival rates.
3. Potted Plant Note: Choose 30-40 cm diameter pots with drainage holes, planting 1 plant per pot to avoid poor ventilation. Add a small amount of decomposed organic fertilizer as base fertilizer during planting to promote growth.

4. Seedling Stage Management: Acclimation & Growth Promotion

The seedling stage (1-2 months after transplanting) is critical for environmental adaptation and robust growth—strengthen management:

• Acclimation Management: Place transplanted seedlings in cool well-ventilated area for 3-5 days to acclimate, avoiding direct sunlight. Gradually increase light until full sun after leaves regain turgidity.
• Water Control: Keep soil slightly moist during seedling stage, strictly prohibit waterlogging. Water in the morning or evening with a spray bottle or along pot edges, avoiding wetting leaves and flowers.
• Fertilizer Management: No fertilization during seedling stage. After acclimation (1 month after transplanting), apply dilute NPK compound fertilizer (1000x concentration) to promote foliage growth—avoid excessive nitrogen which causes leggy growth.
• Weeding & Loosening Soil: Regularly remove weeds to avoid nutrient competition; loosen soil 1-2 times a month to promote root respiration and prevent compaction.
• Thinning & Replenishing Seedlings: For outdoor planting, thin overcrowded seedlings promptly, removing weak or malformed plants to ensure growth space; replenish missing seedlings to maintain full stand.

5. Growth Period Management: Water, Fertilizer & Pruning

From acclimation to budding (3-4 months), Evening Primrose grows rapidly—strengthen management to promote branching and flowering:

6. Flowering & Post-Flowering Management

• Light Management: Ensure 6-8 hours of direct sunlight daily during flowering period. Sufficient light ensures vibrant colors and abundant blooms—provide supplementary light if insufficient.
• Water Control: Keep soil slightly moist during flowering to avoid flower wilting from drought and root rot from waterlogging. Water in the morning or evening.
• Auxiliary Pollination: Evening Primrose is cross-pollinating; outdoor plants rely on nocturnal insects (moths) for natural pollination. For closed home environments, perform artificial pollination in the evening when flowers open—gently dab stamens and stigmas with a cotton swab to improve seed setting rate.
• Post-Flowering Management: Promptly cut off spent flowers and lower branches after blooming to reduce nutrient consumption; retain healthy flower spikes if harvesting seeds, promoting seed development; apply dilute phosphorus-potassium fertilizer to promote plant recovery and provide nutrients for seed maturation.

7. Pest & Disease Control

Evening Primrose is adaptable with few pests and diseases. Common issues and control methods:

(1) Diseases: Root Rot, Leaf Spot, Powdery Mildew

• Prevention: Water reasonably to avoid waterlogging; maintain ventilation and light penetration; avoid overcrowding.
• Control: Spray 800x carbendazim or 1000x thiophanate-methyl at early stage, once every 7-10 days for 2-3 times. For root rot, dig up plants, cut off rotten roots, disinfect, and replant.

(2) Pests: Aphids, Spider Mites, Cabbage Worms, Moth Larvae

• Aphids: Spray 1500x imidacloprid solution.
• Spider Mites: Spray 1000x abamectin solution, focusing on leaf undersides.
• Cabbage Worms & Moth Larvae: Handpick or spray 1000x lambda-cyhalothrin solution.
• Ecological Control: Interplant with pest-repellent plants such as mint and garlic.

8. Harvesting & Utilization

1. Harvest Time: Ornamental flowers—harvest when fully open and most vibrant; cut flowers—harvest at semi-open stage for longer vase life; seeds—harvest when capsules mature (brown color) and tops are about to dehisce, collect promptly to avoid scattering.
2. Harvest Method: Cut cut flowers at stem base with scissors before evening bloom; pick mature capsules for seeds, dry in well-ventilated area, and rub to collect seeds after capsules dehisce.
3. Processing & Utilization: Fresh cut flowers have 3-5 day vase life for floral arrangements; dry seeds for next year’s sowing or processing into health supplements/pharmaceuticals; harvest entire plant during flowering, wash and dry for medicinal use; extract essential oils from flowers for perfumes and aromatherapy.
4. Seed Preservation: Select healthy plants with beautiful flowers, vibrant colors, and no pests/diseases for seed saving. Collect and clean seeds, remove impurities and shrunken grains, store in sealed containers in a dry, cool, well-ventilated place.