Cosmos are fabulous annual flowers for cutting. Their daisy-like blooms add a wild flower touch to flower arrangements, and the feathery foliage makes a great filler. Learn all about planting cosmos seeds for the cut flower garden, to grow and use cosmos for cutting, all season long.
As a gardener and flower grower, I’ve always been captivated by the charm and simplicity of cosmos flowers. The blooms are so delicate, that the sunlight will light up the flowers when seen at the right angle, making them appear to glow in the light.
Depending on the variety, the foliage also has great value, as a filler for flower arrangements. Even before the plants begin to bloom, I find myself harvesting stems to use in bouquets, for a soft and feathery touch.
The flowers come in a variety of colors—from deep pinks to pure whites and striking oranges—ensuring there’s a shade to suit everyone’s taste.
Cosmos also attracts butterflies and other pollinators, adding a lively dimension to your garden as these beautiful creatures make their appearance.
These blooms will always have a place in my garden. The flowers are just so easy to grow, especially from seed, and will also self seed in the right conditions.
In this post I will discuss the process of planting cosmos seeds indoors for the cut flower garden. I will take you through the steps of growing cosmos, from seed to beautiful bloom.
Choosing Your Seeds
Popular Cosmos Varieties
There are a number of different cosmos varieties which you can choose to grow. Cosmos bipinnatus and Cosmos sulphureus are popular for the cut flower garden.
Chocolate cosmos, or Cosmos atrosanguineus, takes a while to produce flowers from seed. Cosmos caudatus produces lots of foliage, and is best used for it’s edible qualities rather than as a cut flower.
Each species of cosmos has it’s own unique characteristics and color palettes. There are tall varieties as well as shorter varieties, depending on the cultivars.
We grow two types of cosmos on the flower farm. Here’s a closer look at the two most popular varieties for cutting:
1. Cosmos bipinnatus:
Cosmos bipinnatus is the most widely recognized type of cosmos, often found growing in cottage type gardens, and of course the cut flower garden. There are lots of different cultivars of these flowers.
This type of cosmos is grown for it’s wide range of colors, including shades of pink, purple, red, and white. The flowers have silky petals and a central eye that is often a different color.
The leaves of Cosmos bipinnatus are finely textured and wispy, adding to it’s soft and airy appearance.
This type grows quite tall, often reaching up to 4 feet in height, making it a great backdrop for any garden setting. The individual stem length is also long, making the flowers a great choice for cutting.
2. Cosmos sulphureus:
The flowers of Cosmos sulphureus have warm tones of yellow, orange, and golden hues. These blooms are slightly smaller and more compact, and the leaves are broader and less feathery than those of Cosmos bipinnatus.
Although this variety of cosmos can also be used as a cut flower, I tend to use it more as an edible flower.
Select The Right Seeds
Choose good quality and fresh seeds. Once you find cosmos plants you love, and grow them for a season, you can harvest your own seeds, to perpetuate the flowers year after year.
Select the colors and varieties that best suit your taste.
Often it takes a bit of growing experience before you find the varieties that you love best, and that grow well in your location. Sometimes the flowers look great in photos, however when you actually grow them they may not make the cut.
This was my experience with cosmos ‘apricot lemonade’. The plants always struggled to produce unblemished flowers in our own location, most likely from the high winds in our area.
Planting Cosmos Seeds
When To Plant
Starting your cosmos seeds indoors will give you a head start on the growing season. As a result you can have earlier blooms from your cosmos plants, depending on the timing of planting.
Sow cosmos seeds approximately 6 weeks before your last spring frost date.
Cosmos is known to be a quantitative short-day flowering plant, especially in immature plants.
What this means is that the flowers will bloom best when the daylight hours shorten to fourteen hours or less, at the end of the summer.
Younger plants are most apt to be sensitive to these shorter daylight hours, and more mature plants are less so.
If you plant your cosmos seeds indoors in late winter, come spring the plants will be more mature than if direct sown, and may also bloom in the long days of summer as well.
How To Plant
I plant cosmos cosmos seeds in cell trays, and grow the seedlings under grow lights until they are ready to be transplanted out. It’s an easy set up that allows me to grow quite a few flowers at the same time.
To plant the seeds:
- Fill the cell trays with a good quality seed starting mix.
- Make a little indent in the center of each cell, either with your finger or an object, into which you will plant the seed. Drop a seed into each little concave space.
- Cover the seeds with soil or vermiculite, because cosmos seeds don’t require light for germination. The vermiculite will help to keep the soil moist while the seeds are germinating.
- Bottom water the cell tray to moisten the soil, and make sure to keep the soil moist until the seeds have germinated. Bottom water thereafter as needed.
- Place on a heat mat, which will warm the soil, and aide in germination. Keep on the heat mat until 60% of the seeds have germinated.
- Then remove from the heat mat, and place under grow lights. Continue to grow under lights, and water as needed, until the seedlings are ready to be transplanted out.
Transplanting Into The Garden
Once the danger of frost has passed for your growing zone, the cosmos seedlings can be hardened off. This will help to acclimate them to the outdoor environment, helping to prevent transplant shock.
Following this process, the young plants will be ready to be transplanted into the garden.
Cosmos are sun-loving plants. Choose a bright and sunny spot for best flowering potential.
Plant into a well drained average soil, and space plants approximately 9 to 12 inches apart.
We grow our cut flowers in rows, and in landscape fabric, for functionality and ease of use. The cosmos do very well in the fabric, which helps to reduce weed pressure.
A cutting garden does not require landscape fabric however, and can be grown in any suitable garden area. Choose a full sun location for your seedlings, and transplant them into your garden.
Water the plants in well after planting. Once they take root and become well established, cosmos are fairly drought tolerant.
Maintenance And Care
Pinching
Cosmos will benefit from pinching, once the seedlings are about 8 to 12 inches high.
By pinching off the central stems or growing tips, down to a set of leaves below, the plants will be stimulated to produce new growth, and more side shoots.
This will result in bushier plants with more flower production.
Deadheading
Deadheading spent flowers, as well as pruning damaged foliage, can improve the appearance of the plant, as well as increase flower production.
Staking
If you live in a windy location, consider providing some support for your cosmos. Staking, corralling, and even flower netting can keep the plants upright during a wind storm.
Harvesting And Cut Flower Care
The stage at which you harvest cosmos flowers is important, for best vase life.
- Harvest when the flowers are just beginning to open, showing some color. You can even harvest in the bud stage if there is some color in the bud.
- I will often remove fully opened flowers from the stem at the time of harvest, because they will not last long in a bouquet.
- Cut long stems, deep into the plant.
- Strip the lower half of the leaves from the stem before placing into water.
- Condition the flowers in water or a holding solution for several hours, or ideally over night. Place in a cool and shaded location while conditioning.
- The foliage of cosmos can also be harvested, even without a flower bud. The foliage makes a great filler, with it’s soft and feathery texture.
- Cosmos are considered to be cut and come again flowers. The more stems that are harvested, the more stems will be produced.
- Vase life is approximately 7 days.
Frequently Asked Questions
How Long Does It Take For Cosmos Seeds To Germinate?
Cosmos seeds typically germinate relatively quickly. Under optimal conditions (ie. fresh seeds, bottom heat), you can expect cosmos seeds to sprout within 7 to 14 days.
Can Cosmos Be Grown In Containers?
Yes, cosmos can be successfully grown in containers. This makes them a great choice for gardeners who may not have a lot of ground space, such as those with balconies or patios.
Make sure the container is large enough to accommodate the growth of cosmos, which can grow to 4 feet in height depending on the variety.
While cosmos are relatively drought-tolerant, container-grown plants dry out faster than those in the ground. Regular watering is important, especially during hot, dry periods.
How Tall Will Cosmos Plants Grow?
The height of cosmos plants can vary depending on the species and variety.
Cosmos bipinnatus can reach heights ranging from about 2 to 4 feet (60 to 120 cm). Some taller varieties may grow up to 5 feet (150 cm) under optimal conditions.
Cosmos sulphureus are typically shorter than Cosmos bipinnatus, usually growing between 1 to 3 feet (30 to 90 cm) tall.
Conclusion
Planting cosmos from seed is a great gardening project for the cut flower garden. Cosmos is an excellent cut flower, with many varieties to choose from.
The plants grow quickly from seeds to seedlings. Before long, it’s time to harden them off and plant them out.
Not only are these blooms a joy to grow as cut flowers, they are also wonderful to experience in the garden itself.
These ethereal blooms not only offer a display of beautiful color, but they glow in the sunlight, and attract a host of beneficial pollinators to the garden beds as well.
So, sow your cosmos seeds, and watch your garden transform into a canvas of color and life. Happy planting, and may your garden flourish with the beauty of your wonderful cosmos flowers.
Have you ever started your cosmos by planting the seeds indoors? Be sure to leave a comment below to share your experience!
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