Cosmos Sulphureus: Bright Yellow Flowers for a Vibrant Garden

Cosmos sulphureus or Sulfur Cosmos is also known as Klondike Cosmos, Yellow Cosmos and Orange Cosmos. It is a fast-growing annual, widely used as an ornamental plant for borders and flower beds. Sulphur cosmos has 2- to 3-inch orange, red or yellow single blooms and grows 1-6 feet tall. Sulphur cosmos are not impacted by drought or neglect, making them ideal for summer pollinator planting. Sulfur cosmos belongs to the Asteraceae Family (Daisy/Sunflower). The compound leaves are between 6-12 inches long with deeply cleft leaflets. The plant is native to Mexico, Central America and northern South America and naturalised in other parts of North and South America, Europe, Asia and Australia.

Some popular cultivars of this species are compacted to dwarf plants with semi-double to double orange-yellow or red flowers. The genus name, Cosmos, comes from the Greek word ‘cosmos’, meaning beautiful. The specific epithet, sulphureus, is the Latin word for sulphur and refers to the flower colour. The flower blooms are long-lasting and versatile, ideal as a border plant, or a cut flower for indoors and in flower beds. They can also be grown in a container in full sun. Cosmos flowers attract beneficial insects like lacewings, parasitic wasps, tachinid flies and hoverflies that feed on insects and help in pollination. If you allow your plants to die naturally, the dead flowers will fall into the soil. When the conditions are right, cosmos seeds will germinate.

See also: All about Zinnia Elegans

Read: about Cosmos Bipinnatus

see also all about Yellow Daisy

Cosmos sulphureus – Key facts 

Read also: Common summer flowers in India  

Cosmos sulphureus – Maintenance

Cosmos sulphureus is a low-maintenance plant. Sulfur cosmos has a growth pattern in which each plant has numerous flowers at different stages of development, from buds to fully open, maturing flower heads to seed maturation and shedding.

Sunlight

Cosmos needs full sun with at least 6-8 hours of sunlight. They can grow in partial shade but tend to get leggy after a few blooms. Cosmos are dry and warm-weather plants.

Soil and fertiliser

Cosmos sulphureus prefers neutral to slightly acidic soil but will tolerate poor soil. They grow easily in average, medium moisture, well-drained soils in full sun. Avoid planting them in rich fertile soils as they may grow too tall and droop over. Overly fertile soil can lead to plants with strong stems and leaves but few flowers.

Water

Cosmos sulphureus can tolerate a certain amount of drought and needs moderate water for daily care. In summer, water frequently. Even in tough, hot or dry conditions with little water they seem to flower. Always aim your watering can at the base of the stems. This helps avoid water splashing on the foliage or flowers.

Deadheading

Regularly deadhead the flowers. Just pinch off the dry, dead flower heads that contain seeds. This encourages new growth and more flowers. If the plant grows tall, it is better to provide a trellis support or a fence to lean on.

Pest and disease prevention

If grown properly, Cosmos sulphureus does not suffer from any serious insect or disease problems. But it may occasionally be attacked by aphids or red spider mites, which can be treated with insecticide soaps. Aphids can quickly infest and spread disease. To get rid of aphids, pour a strong stream of water. Powdery mildew can also be a problem during warm, humid conditions. To prevent powdery mildew, ensure that the plants have good circulation and bright light. If left in wet soil, they can suffer from fungal infections and root rot. Drooping or yellowing foliage is a common symptom of root rot, which occurs when Cosmos sulphureus has waterlogged soil. If the plant has fungus, use a horticultural fungicide. Cosmos may be susceptible to grey mould or mildew. Remove affected discoloured leaves and, if necessary, plants too. Slugs are a common pest that feeds on cosmos sulphureus. They will make small holes in the leaves. To control slugs, remove weeds and apply lime powder on infested flowerbeds.

Read how to grow and maintain Floribunda rose

Cosmos sulphureus – Propagation from seeds and cuttings

New Cosmos sulphureus can be grown from seeds. Potted plants are easily available in nurseries and can be planted at any time in gardens and containers.

Lightly cover the seeds with soil and thin out the seedlings to space them correctly. Cosmos grow quickly and modern hybrids can start blooming within 10 weeks of sowing. But in some climates cosmos sown in spring may not bloom until late summer. When you decide to grow a single plant, provide at least 8 cm of space on each side. Water well and keep the soil moist for 5-10 days after seeding. Seeds germinate in three weeks and bloom in two months.

To propagate from a Cosmos sulphureus cutting, use sharp scissors and a clean glass of water. Cut a couple of 6-inch shoots of new growth. Remove the leaves from the bottom half of the stem. Place it in a glass of water and ensure that the cleaned spots are underwater. Keep the glass on a bright window sill and change the water every few days. In a couple of weeks, roots will emerge. Transplant it into a pot.

Cosmos sulphureus – Uses

• Cosmos sulphureus is a showy plant. It is commonly seen along roadsides, beds and borders in many countries, especially in Korea and Japan.
• These plants attract pollinators so planting them with vegetable crops that require insect pollination can be beneficial.
• Cosmos sulphureus has edible flowers and young leaves and are used to add a dash of colour to salads or fruit dishes. The leaves are used in traditional malaria medicine in Indonesia and Brazil. In Thailand, the flowers are a source of anti-microbial compounds and consuming them helps to treat various diseases.
• The flower heads have flavonoid pigments, which make them a natural source of yellow and orange wool dye.

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