Quick Reference

Type of Harvest: Continuous harvest

Transplant/Direct Sow: Direct sow or transplant

When to Plant: Start seeds indoors 8 weeks before the average last frost date for spring planting. Direct sow seeds when outside temps are around 70°F.

Days to Germinate: 7-10 days

Days to Maturity: 60-90 days

Planting Depth: ½ ” deep

Germination Temp:70°F

Seed Spacing: Plant 3” apart. Thin to 12” apart.

Row Spacing: 2-3' apart or against a fence.

Light: Full sun

Soil pH: 6.0-6.8 pH

Water: 1- 1 ½” of water per week

Soil Temperature: Minimum 70°F. These are cool weather loving plants.

Fertilizer: No fertilizer - it will weaken the plant.

Rotation: Not needed for cosmos, which are flowering plants that like poor soil.


Harvest Type

Cosmos will produce flowers once the weather warms until the first frost.

Transplant / Direct Sow

In the spring, start seeds indoors about eight weeks before the average last frost date. Because cosmos do not tolerate frost, there is no real option for fall planting. Direct sow cosmos seeds when the outside temperature is around 70°F.


Full Sun

When to Plant:

Transplant or direct sow seeds when the soil temperature is 70°F.

Days to germinate

It takes most Cosmos cultivars 7-10 days to sprout.

Days to maturity

It takes about 60-90 days for cosmos seeds to bloom.

Planting Depth

Plant seeds 1/2" deep.

Germination Temperature Range

Germination is best when the soil is 70°F.

Spacing Between Plants

Plant seeds 2" apart and thin to 12-18". Cosmos has a narror root zone but becomes a broad plant. For best bloom production, space plants 18 inches apart.

TIP: Cosmos are tall and lanky plants. Plant them on a trellis or along a fence.

Companion Plants

Zinnia, sunflowers, and verbena make excellent companion plants for cosmos.

Growing conditions

Cosmos like poor soil. Don't over water them, or they will drop blooms. Hard, clay and poor soil are ideal for cosmos.

Tip: Cosmos are excellent for attracting pollinators. If you plant cosmos around your garden you will attract pollinators to ever zone of your garden and that can increase yields.


There is no real need to rotate cosmos as they like poor soil. You can rotate them throughout your garden in places where heavy feeders have grown. Rotating them helps bring in pollinators to all parts of your garden.

Anticipated yields

Plan your garden yield at 40 blooms per plant for cosmos. Cosmos will continue to bloom throughout the warm summer and fall and die when frost occurs. Dead heading cosmos is one way to increase the number of quality blooms from each plant.

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