Growing Cosmos bipinnatus: Tips for Abundant Blooms

Cosmos bipinnatus, commonly known as Cosmos, Autumn Cosmos, or Mexican Aster, is a species of flowering plant in the Asteraceae family, originating from Mexico.

There are several horticultural varieties, including white-flowered Cosmos, large-flowered Cosmos, and purple-flowered Cosmos. These are further categorized into early-blooming and late-blooming types, as well as single and double-petaled types.

Cosmos are sun-loving plants, tolerant of poor soil, but not fond of too much fertilizer. Too fertile soil can lead to overgrowth and fewer flowers.

They also dislike hot, waterlogged conditions and are not suited to high summer temperatures or cold climates. The flowering season is during the summer and autumn seasons.

I. Growth and Distribution

Cosmos bipinnatus

This plant thrives in sunlight, is cold-sensitive, frost-intolerant, and dislikes extreme heat. It tolerates thin soil but excessive fertilization and watering can lead to excessive growth with fewer flowers, and might even cause the plant to fall over. This type of daisy can propagate extensively through self-seeding.

II. Morphology and Characteristics

This annual herbaceous plant has a slender upright stem with many branches, which could either be smooth or slightly hairy.The leaves are single, opposite, about 10cm long, and twice pinnate, with narrow, entire, toothless segments.

The head-like inflorescences are borne on slender stems, either terminal or axillary, with stems 5-8cm long. The involucres are two-layered, with membranous edges to the inner layer.

The ray florets are arranged in one row, with toothed petal tips and 8 petals in total, which are white, pink, or deep red. The disc florets occupying the central part of the flower head are all yellow.

The achene has a beak, and the seeds have a lifespan of 3-4 years. The dry grain weight is 6g. The flowering season is in the summer and autumn.

Cosmos bipinnatus

In horticultural varieties, there are white-flowered Cosmos, large-flowered Cosmos, and purple-flowered Cosmos. These varieties are divided into early-blooming and late-blooming types, as well as single and double-petaled types.

The Mexican Aster (Cosmos bipinnatus) is a member of the Asteraceae family, an annual herbaceous plant, over 1 meter tall, found in wild populations, flowering from August to October in high-altitude regions.

Cosmos bipinnatus is native to Mexico. In 1799, a Spanish priest named it COSMOS, which means ornament or medal in Greek, but in English, it means universe.

Due to the strong adaptability and reproduction of Cosmos, it has been domesticated as a wildflower in many countries around the world, and it indeed lives up to its reputation as the “flower of the universe”.

Cosmos bipinnatus

Because they are easy to cultivate and can grow as long as there is enough sunlight, Cosmos have become a common wildflower seen everywhere. With diverse colors and large-scale planting, they create a sea of flowers when in full bloom.

The shape of the flowers is similar to cherry blossoms, so they are also called “Autumn Cherry Blossoms”, and they are deeply loved by the public.

III. Cultivation Method

Cosmos is a hardy plant that thrives in sunlight and can withstand drought. It doesn’t have strict soil requirements but cannot tolerate waterlogging. Planting it in fertile soil can lead to overgrowth of branches and leaves, which can affect the quality of the blooms.

When the seedling reaches a height of 5 centimeters, it’s ready for transplanting, and it should be settled when it has 7-8 leaves. Alternatively, you can thin out the seedlings after direct sowing.

If base fertilizer is added to the planting area, there’s no need to fertilize during the growth period. Over-fertilizing the soil can lead to excessive growth of branches and leaves and reduce blooming. Or, you can apply mature urine diluted with five times the amount of water every ten days during the growing period.

Watering 2-3 times during dry periods will ensure healthy growth and abundant flowering. However, during the high-temperature months of July and August, the flowers are unlikely to produce seeds.

Seeds mature quickly and fall off easily, so they should be harvested in the early morning. Cosmos is a short-day plant. Plants sown in spring often have lush leaves but few flowers, while those sown in summer are short, neat, and continuously blooming. They grow rapidly and can be pruned multiple times to increase branching.

Cosmos plants are tall and should be staked to prevent them from falling over or breaking in windy locations.

Typically, they are grown as short plants by topping them when they reach 20-30 cm in height, and subsequently removing the new top buds several times to dwarf the plants; this also increases the number of flowers.

The planting area should be slightly fertilized. Harvest seeds when the fruit slightly turns black to prevent them from scattering after maturation.

IV. Propagation Method

Cosmos is propagated by seeds. Sowing is typically done in early spring, with flowering from May to June. From August to September, the hot, rainy weather reduces flowering. After cooling in the fall, flowering continues until frost.

If sown in July or August, the plants can flower in October, and the plants are short and neat. Cosmos seeds can self-sow. Once planted, they will produce a large number of self-sown seedlings.

With a little protection, they can flower as usual. Direct sowing in open ground beds can be done in mid-April, and if the temperature is suitable, seedlings can emerge in 6-7 days.

During the growing period, propagation can also be done by cuttings. Healthy branch tips about 15 cm long can be cut below the node and inserted into sandy soil. Provide some shade and maintain humidity, and the cuttings should root within 5-6 days.

Spring sowing in April results in rapid germination, usually within 7-10 days after sowing. Propagation can also be done with softwood cuttings, which root 15-18 days after insertion.

When the seedlings have 4-5 true leaves, they can be transplanted and topped. As with direct sowing, if base fertilizer is added to the planting area, there’s no need to fertilize during the growth period. Over-fertilizing the soil can lead to excessive growth of branches and leaves and reduce blooming.

During the high-temperature months of July and August, the flowers are unlikely to produce seeds. Seeds mature quickly and fall off easily, so they should be harvested in the early morning. Cosmos is a short-day plant.

Plants sown in spring often have lush leaves but few flowers, while those sown in summer are short, neat, and continuously blooming.

V. Value and Others

Flower Language

Flower Language: The heart of a maiden, maiden’s innocence, strength, purity, nobility, freedom, cheerfulness, eternal happiness.

Flower Legends: European maidens often include a Persian chrysanthemum in their love letters. A single flower carries the maiden’s budding emotions, shy yet hopeful, joyful yet anxious.

Gifting Etiquette: Arrange a variety of Persian chrysanthemums in a glass salad dish, garnished with several types of grapes. Tie white and pink ribbons around the dish.

The scientific name for Persian chrysanthemum signifies beauty and harmony. Originally a plant that blooms in autumn with short daylight hours, it now has many early blooming varieties. The colors include red, yellow, pink, white and multicolored, making it a vibrant and diverse flower.

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