Calendula, commonly known as Marigold, has the scientific name *Calendula officinalis*. It is native to Southern Europe and extends to Iran. Belonging to the Compositae family, this plant is a one- or two-year herb that thrives in cool, moist conditions and is cold-resistant. It prefers well-drained soil and is adaptable to various growing environments.
The plant typically grows between 20-35 cm tall, with long ovate leaves that clasp the base. The flowers are borne on a single stem at the top, with flower stems measuring about 6-10 cm. The blossoms are either single or double, with a flat or rounded shape. Flowering occurs from December to March, making it an ideal choice for winter and spring flower beds. In regions like Jiangsu and Zhejiang, where climate can be unpredictable, Calendula is mainly used for the "New Year's Day" and "Spring Festival" seasons. However, it performs poorly during the "May 1st" holiday due to high temperatures. Popular varieties include "Big Stick," "Black Eye," and "Banquet," featuring vibrant yellow and orange hues. The "Big Stick" variety blooms about 10-14 days earlier than other types.
For seed sowing, Calendula seeds are small, with approximately 130-170 seeds per gram, shaped like a star. Winter and spring blooms are usually started in September or October to ensure flowers in late winter and early spring. Seedlings are often raised in protected areas using bed seeding or tray cultivation. A soilless substrate is commonly used, with a pH of 6.0-6.8 and an EC value of 0.5-0.75. After sowing, covering the seeds with vermiculite helps improve germination. The medium should maintain 60-70% humidity, and germination typically occurs within 8-15 days.
In the first growth stage, after germination (4-6 days post-sowing), the medium should remain slightly dry to prevent rot. The temperature should be maintained at 20-25°C, and light is essential—no shading needed unless planting in September, when some cooling may be beneficial.
During the second stage, moisture is still important but less than in the first stage. This allows roots to grow into the medium without disturbance. Once the first pair of true leaves appears, a diluted fertilizer solution (50 ppm of 20-10-20) can be applied.
The third stage marks rapid growth, requiring more water and nutrients. Alternating between 50-100 ppm of 20-10-20 and 14-0-14 water-soluble fertilizers helps reduce salt buildup. Watering should alternate between wet and dry to encourage strong root development. The temperature can be lowered slightly to around 18°C. At this point, there are 2-3 pairs of true leaves, and the seedlings reach 3-4 cm in height, with roots extending up to 3-5 cm.
In the fourth stage, the seedlings enter a refinement period. Root growth is nearly complete, and watering should be carefully controlled. A 14-0-14 flower-specific fertilizer is recommended. Temperature and humidity are slightly reduced compared to previous stages, and proper ventilation is crucial to prevent disease.
Transplanting or potting up occurs after this phase. Calendula is typically grown in 12-13 cm diameter containers, and once planted, it rarely needs repotting. If spreading seedlings, a 128- or 288-cell tray is used before moving to the final container. A small amount of compound fertilizer can be mixed into the medium as a base.
Calendula is a full-sun plant and requires plenty of light for optimal growth and flowering. After transplanting, the temperature should be kept around 15°C. Since it’s a cool-season plant, no additional heating is needed in the greenhouse, but protection from freezing is essential. If the temperature drops too low, flowering may be delayed.
Water and fertilizer management is key. The growing medium must have good drainage and water retention. Watering should be done in a way that allows the medium to dry slightly between waterings, which promotes healthy root growth. Fertilization should alternate between 20-10-20 and 14-0-14 at 200-250 ppm every 7-10 days. During colder months, less 20-10-20 fertilizer is used. Calendula is sensitive to trace elements, which can cause chlorosis and leaf yellowing, reducing its ornamental value.
Pruning is generally not required, as it naturally produces neat flowers. However, outside of Jiangsu and Zhejiang, topping can be done to encourage branching, leaving 4-5 leaves. Winter care includes keeping the plants warm to maintain green foliage and flowers, while ensuring good air circulation.
Common pests and diseases include rickets, gray mold, bacterial blight, powdery mildew, anthracnose, and aphids. Preventative treatments such as Plectranthus, chlorothalonil, and Bordeaux mixture are effective. For aphids, a 40% omethoate solution at 1000 times dilution works well.
Quality standards for Calendula include a well-developed flower color and a crown width of 15-20 cm. The plant should appear neat, with bright green leaves. To maintain quality, transportation should not exceed 12 hours. If the first bloom is not sold, it can be trimmed and still be marketable.
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