Cosmos are charming annual flowers with colorful, daisy-like blooms perched on long, slender stems. Blooming from summer through fall, they attract birds, bees, and butterflies, adding life and vibrancy to gardens.

These low-maintenance plants grow easily from seeds and thrive even in poor soil conditions. Here's how to plant and grow cosmos successfully.

About Cosmos

A member of the Asteraceae family, cosmos are native to Mexico and are also known as Mexican asters. These plants produce 3- to 5-inch daisy-like flowers in various colors, including pink, orange, red, yellow, white, and maroon. Their flowerheads may be bowl- or open-cup-shaped, and the plants can reach heights of up to 6 feet.

Planting

Cosmos thrive in well-draining soil and do not require special soil preparation. They prefer soil that is not too rich, as overly fertile soil encourages foliage growth at the expense of blooms. These plants are tolerant of most soil pH levels, performing best in neutral to alkaline soils with a pH of 7.0–7.5. Cosmos are also highly drought-tolerant and can withstand warm, dry weather.

When to Plant Cosmos

Sow seeds outdoors after the danger of frost has passed.

For an earlier start, sow seeds indoors 4–6 weeks before the last spring frost date in seed trays or pots. Transfer seedlings to 5-inch pots once they reach 3–4 inches in height.

Young transplants can be planted outdoors once frost risks are over.

How to Plant Cosmos

Sow seeds no more than 1/4-inch deep.

Thin seedlings to 12–18 inches apart once they are a few inches tall.

Plan spacing based on variety, as cosmos can grow between 18–60 inches tall.

Cosmos from seeds will take about 7 weeks to bloom and continue flowering until the first fall frost.

Growing

Dear Lykkers, to ensure a continuous and healthy bloom, follow these care tips:

Deadheading and Pruning

Deadhead faded flowers to promote faster flowering and better branching. For taller varieties, consider staking or growing against a fence for support. Pinching out central shoots can also encourage balanced growth.

Watering

Water regularly until plants are well-established, especially during dry spells. Avoid overwatering, as it can reduce flowering and encourage excessive foliage growth.

Managing Self-Seeding

Cosmos self-seed easily, which can lead to weedy beds. Remove spent flowers before they go to seed or thin out seedlings in the spring to maintain a tidy garden.

Types

‘Picotee’: White flowers with a crimson border or flecks of crimson.

‘Sea Shells’: White, pink, or red blooms with tube-shaped petals.

‘Purity’: Classic white flowers, stunning when paired with dark-maroon hollyhock or purple basil.

‘Cosmos Sonata Series’: Complements Bells of Ireland beautifully.

‘Chocolate’ Cosmos: Distinct dark hues, pairing well with white campanula or dianthus.

Tall Cosmos: Ideal for the back of gardens or mixed borders with perennials like phlox and delphiniums or annuals like asters.

Dwarf Cosmos: Suitable for zinnias, pansies, or dark-blue morning glory.

Harvesting

Harvesting Seeds

Leave some flowers on the plant to self-seed for future blooms.

Cut Flowers

Harvest flowers once the petals have just opened for the longest vase life, lasting over a week in water. Remove lower leaves before placing them in vases.

Cosmos bring the heart of summer into gardens, offering vibrant colors and an elegant charm that enhances bouquets and landscapes alike.