How To Grow Chocolate Cosmos From Seeds

Chocolate cosmos (Cosmos atrosanguineus) are all among the most rare flowers in the world, featuring a dark reddish brown color, almost black centers, and have a chocolate scent. 

Cosmos is enjoyed as a wonderful ornamental plant which attracts butterflies.

They have captivated gardeners since they were first discovered in Mexico during the mid-1800’s. 

The seeds germinate quickly and produce healthy, productive plants when sown and cared for correctly.

Cosmos require 5 to 7 days to germinate indoors and up to 14 days outdoors. The seedlings grow quickly and reach a size suitable for transplanting within four to six weeks of germination.

Chocolate cosmos should be planted in a warm, sheltered location with all day sun. In northern areas you may want to give them a head start by planting the tubers in pots several weeks before bringing them outdoors.

Chocolate cosmos are tender perennials and winter hardy only in zones 9-11.

If the plants are grown in very well-drained soil and are heavily mulched, they may survive the winter in zones 7-8. For best results, dig the tubers in fall and store them indoors for the winter where they can be kept cool and dry.

If the tubers eventually become crowded, they may be divided. This can be done in fall or spring. Make sure each tuber is attached to some viable stem tissue and has one or more “eyes."

Chocolate cosmos can take several years to mature. If you overwinter the tubers indoors you will usually get a larger plant and more flowers the next year.

You can also use them as a fast-growing annual hedge or in a cutting garden.

Since the taller cultivars are not always uniform in height, they’re perfect for adding an informal look to cottage gardens.

Shorter cultivars of both species are ideal near the front of the border, in containers, or as edgings.

How To Plant Cosmos From Seeds:

In mild climates, sow the seeds indoors four to six weeks before the preferred outdoor planting time in late spring, which should be after the soil has dried out and is no longer soggy. In areas that experience freezing temperatures, sow seeds indoors four weeks before the last frost and transplant them outside two weeks after the last frost date.

You can start seeds indoors, four to six weeks before the last frost, but cosmos sown outdoors directly in the garden will quickly catch up.

 

Sowing Chocolate Cosmos Seed Indoors:

✅ The seeds don't require deep planting. Sow the seeds on the surface of the pot or tray in a soil-less sterile seed compost which is thoroughly moistened before use, to prevent fungal problems on the developing plants. 
✅ Then, cover with a thin (3mm) layer of fine compost or vermiculite 
✅ Keep the soil moist at 65 F (18C). Maintaining a soil temperature of 65 degrees Fahrenheit encourages quick and even germination. Watering the soil prior to seeding then keeping the pots covered with a plastic bag conserves the soil moisture so the seedlings won't require watering until after they sprout. 
✅ Keep the pot covered with a kitchen foil until germination starts, so that the compost stays moist. Drying of the soil surface at this stage usually stops further germination and is probably a common cause of failure.

✅ Cosmos require up to 14 days to germinate. The seedlings grow quickly and reach a size suitable for transplanting within four to six weeks of germination.

✅ The plants don't require light until after they sprout, so you can keep the pots in a warm but dark room until they begin to emerge.

As soon as the seedlings emerge, provide plenty of light on a sunny windowsill or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Most plants require a dark period to grow, do not leave lights on for 24 hours.

✅ Before planting in the garden, seedling plants need to be “hardened off”.
Leave them out for a few hours each day, gradually increasing the length of time over the course of two weeks. 
✅ Then accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night bring containers indoors, then take them out again in the morning. This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.
✅ Then, transplant them 12 inches apart in a sunny bed with rich, fast-draining soil once the soil warms up.

 

Sowing Chocolate Cosmos Seed Directly In The Garden After Frost:

✅ Direct sow seeds in average soil in full sun after danger of heavy frost gone.
Select a location in full sun to part shade with good rich well-drained organic soil protected from wind.

✅ Prepare the bed by turning the soil under to a depth of 8 inches. Level with a rake to remove clumps of grass and stones.

Most plants respond well to soils amended with organic matter. Compost is a wonderful form of organic matter with a good balance of nutrients and an ideal pH level, it can be added to your planting area at any time. If compost is not available, top dress the soil after planting with 1-2 inches of organic mulch, which will begin to breakdown into compost. After the growing season, a soil test will indicate what soil amendments are needed for the following season.

✅ Sow seeds 4 inches apart and ¼ inch deep. The small seeds don't require deep planting. Placing the seeds on top the soil in the pot and placing just enough soil on top to cover them is sufficient. 

✅ Firm soil lightly, water and keep evenly moist by light spraying. Mulches also help retain soil moisture and maintain even soil temperatures.

✅ Seedlings will emerge in 7-14 days. The seeds may take up to 14 days to germinate depending on soil moisture.

✅ Thin plants to stand 10-12 inches when seedlings are 1 inch high.

✅ For annuals an organic mulch of shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.

✅ Keep soil evenly moist but not wet. Cosmos plants can withstand heat and drought conditions and should not be overwatered. Too much water will cause the roots to rot, but a once a week deep watering will keep them healthy and happy. Make sure to let the soil dry out between waterings as Cosmos flowers originated in a dry area.

✅ Avoid fertilizer, which will encourage the plants to produce foliage rather than flowers. After plants are about 6 inches tall, a light fertilizer may be applied. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release fertilizer, as higher rates may encourage root rots.

✅ Tall cultivars may need staking to prevent their thick, hollow stems from breaking due to heavy rain or wind.

✅ Pinch off spent flowers to encourage continuous bloom. Pinching stem tips can reduce height and encourage branching but isn’t necessary. Deadheading is recommended since it lengthens the bloom season. Cosmos plants that aren’t deadheaded will self-sow in warm regions. 

✅ If you are growing chocolate cosmos flowers as an annual, the best time to look for this is when you dig them up in the fall. If you are growing chocolate cosmos flowers as a perennial, every couple of years you can dig them up and divide them in early spring.

✅ Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating. 

✅ Remove plants after they are killed by heavy frost in fall to avoid disease issues the following year.

✅ Monitor for pests and diseases. Check with your local Service for pest controls recommended for your area.

 

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