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All About Cosmos

all about cosmos

Cosmos are Equally at Home in a Garden Bed or Open Meadow

Cosmos Wildflowers are October’s birth flower and belongs to the genus known as Compositae, of which there are 20 known species. All are members of the Asteraceae family, of which there are more than 23,500 varieties, including the aster, daisy, and sunflower family. Cosmos is an herbaceous perennial plant and also an annual that will grow between 1 foot to 7 feet tall, depending on the species.

Most home gardeners are familiar with the two annual species, which while not usually winter hardy, may readily self-seed during a mild season:

  • Cosmos sulphureus (C. sulphureus) blooms in shades of yellow, orange and red, with small flat leaves.
  • Cosmos bipinatus (C. bipinatus) typically blooms in white, or various shades of pink to dark rose. Bipinatus has finely-cut ferny foliage and typically grows taller.

Easy to grow from seed, Cosmos thrives in full sun and moderate soil, requiring little attention once it is established, making them ideal for water conservation landscapes and arid conditions.

Native to the southwestern deserts and Mexico, they have spread all over the United States and Europe.

All About Cosmos: Origins

During the 16th Century, Spanish explorers discovered Cosmos and brought the wild species back to Madrid from Mexico. The flower eventually made its way to England in 1789, thanks to the wife of the English ambassador to Spain, and arrived in the United States during the mid-1800's.

Cosmos is a member of the Asteraceae family, which refers to the classical Latin word aster, or “star” - an apt description of the star-like form of the blossom. While most members of the Asteraceae family are flowers, shrubs, vines and trees are also inluded.

Many of the plants in the Asteraceae family are merely ornamental; however others are often useful as well as beautiful, and grown for production:

  • Cooking oils (sunflower)
  • Sweetening agents (Stevia)
  • Coffee substitutes (chicory)
  • Herbal medicines (Calendula and Echinachea)
field of cosmos in front of the ritz carlton

Field of Cosmos in bloom at the Ritz Carlton hotel in Miami, Florida.

Different Species of Cosmos

The Genus name, Cosmos, comes from the Greek word “kosmos” meaning "beautiful", or “harmony”. The flower represents peace and love.

The leaves of Cosmos are simple or pinnate, arranged in opposite pairs, and the flowers are composite flowers, with a central disc surrounded by a ring of petals. The color varies with the different species, and Cosmos are often found growing naturalized in meadows. Many of these wild discoveries have been cultivated and become popular bedding plants in the ornamental flower garden.

Cosmos are traditional cottage garden plants, perfect for informal color either in the front or mid-section of the garden. Flower forms are typically single, in a bowl or cup shape, atop long stems that make them ideal for cutting and arranging in bouquets.

Keep plants trimmed of spent blossoms, and they will continue to produce blooms over a long season.

The most common C. bipinatus, varieties include:

  • Sensation, with showy blossoms in various shade of pink.
  • Picotee, with a profuse display of white petals, edged in a crimson border.
  • Sea Shells, a fairly recent introduction with show stopping display of tubular petals in shade of white, pink or red and Purity, showcasing all white flowers.

C. bipinatus grow tall and are ideally planted in the back of a border along with lilies, ornamental grasses, cleome, and dahlias. For a perfect mid-border plant, breeders have created the Sonata series, bred to be shorter and sturdier. Sonata is also ideal for pots or smaller gardens.

An alternative to the pink and white blossoms would be Cosmos Orange, found in the C. sulphureus varieties, which include plants in the “Ladybird Dwarf,” and the “Klondyke Mix". Both range in shades of yellow to orange to scarlet.

sulphur cosmos

Sulphur cosmos being visited by a bee.

Often found in wildflower mixes, Orange Cosmos has a cherry-orange blossom and forms bushy low-growing plants. When harvested, the blossoms are easily pressed and dried for making gift cards and crafts. Plant Orange Cosmos alongside zinnia, pansies or Johnny Jump –ups for a burst of bright color in the front of a border or rock garden.

A popular perennial is Chocolate Cosmos ( C. Altrosanguineus), which blooms in a deep maroon brown, and is especially nice when planted with dianthus, poppies and white daisies.

All About Growing Cosmos

Germination can take between 7-21 days, at optimal temperatures of 75*. Flowering begins 50-60 days after germination. Sow seeds indoors 4-5 weeks before the last spring frost date, or outdoors in the garden after danger of frost has passed.

In the garden, space plants 1 – 2 feet apart, or closer for the shorter types. When planted closely, the large branching stems will support each other, yet are susceptible to gray mold which can spread quickly when conditions are too moist. To curb the development of mold, allow for spacing to ensure that there is enough air circulating in between plants.

Soil that is too rich will yield fast plant growth, yet can weaken stems and create a scarcity of flowers. For this reason, it's best to grow Cosmos in soil that is not overly fertilized. While young plants need moisture to get started, allow mature plants to dry out in between watering, as their developing roots are capable of accessing groundwater on their own. Provide the taller varieties protection from the wind and be prepared to stake plants to keep the thick hollow stems from breaking in heavy rain or wind.

Properly spaced plants will encourage good air circulation. If mold appears, remove infected plants immediately to stop the disease from spreading, as they are unlikely to recover.

It's easy to save the seeds of Cosmos; however, since many home garden varieties are hybrids, the flowers won’t always come back true and will often revert to the original single flower form. Cosmos are attractive to beneficial insects and butterflies, which makes them ideal for wildflower mixes and naturalizing.

Keep them cut back after first bloom, to prompt new and continuous growth, and when pruning spent flower heads, instead of just removing the blossoms, trim a third of the way down, water and wait for a new crop.

About the Author: Ellen Ecker Ogden is the author of six books, including The Complete Kitchen Garden, featuring theme gardens and recipes for cooks who love to garden. She writes and lectures on kitchen garden design.

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