When to Plant Cosmos in Clarks Hill, South Carolina (29821)

Location

Clarks Hill, South Carolina

ZIP Code

29821

USDA Zone

Last Frost

Sunday, March 15, 2026

📅 Your 2026 Planting Dates

Direct Sow Outdoors

Sunday, March 15, 2026

Based on last frost Sunday, March 15, 2026 · Zone 8b

Pro tip: Sow Cosmos directly outdoors around your last frost date when soil starts to warm.

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🌿 Plant Details

Scientific Name Cosmos bipinnatus

Days to Maturity 60 days

Mature Height 24-60"

Spread 18"

Type Annual

☀️ Growing Requirements

☀️

Sun

Full Sun (6-8 hours)

💧

Water

Low-Moderate

↔️

Spacing

18" apart

🌱

Planting Depth

0.25" deep

Seeds typically germinate in 7-14 days

Ready to Plant Cosmos in Clarks Hill?

Get your seeds now so they're ready by Sunday, March 15, 2026.

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🤝 Good Companions

CornSquashTomato

🤝

Full Companion Planting Guide for Cosmos

See which plants help Cosmos thrive, which to keep away, and raised bed layout tips →

🛠️ Supplies You'll Need

🌍 Flower Garden Soil ✂️ Pruning Shears 🚿 Watering Can

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🌾 Seed Saving Guide

🟢 Easy

✅ Open-pollinated — seeds grow true to parent

When to Harvest Seed

Harvest narrow seed heads when flower petals drop and the base turns brown and dry.

Processing

Pull seeds directly from dried flower heads, dry 1 week in an open envelope.

Seed Viability

Up to 3 years when stored cool, dark, and dry.

Pro Tip

Cosmos cross freely within the species — isolate by 150 feet from other cosmos for pure color.

🪴

Raised Bed Planting Guides

A 4×8 bed fits 14 plants of Cosmos. See plant counts, spacing grids, and companion pairings for every bed size →

Frequently Asked Questions

When should I plant Cosmos in Clarks Hill, South Carolina? +

In Clarks Hill (Zone 8b), direct sow Cosmos outdoors around Sunday, March 15, 2026.

What is the last frost date for Clarks Hill, South Carolina? +

The average last spring frost date for Clarks Hill, South Carolina (ZIP 29821) is around Sunday, March 15, 2026. This is based on NOAA climate normals for USDA Zone 8b.

How long does Cosmos take to grow? +

Cosmos typically matures in about 60 days from direct sowing. In Clarks Hill, that means you can expect harvest around Sunday, March 15, 2026 plus 60 days.

Should I start Cosmos indoors or direct sow in South Carolina? +

Cosmos does best when direct sown outdoors. In Clarks Hill, sow directly around Sunday, March 15, 2026.

📚 More Cosmos Planting Guides

🗺️

Cosmos in South Carolina

Zone-by-zone breakdown · Full state guide

→ 🌡️

Zone 8b Cosmos Guide

All cities in your zone · Avg dates

→

Other Plants for Clarks Hill

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Growing Cosmos in Zone 8b

Cosmos (Cosmos bipinnatus) is a popular garden vegetable. In Clarks Hill, South Carolina, which is in USDA Hardiness Zone 8b, you should direct sow seeds around Sunday, March 15, 2026.

Your average last frost date is Sunday, March 15, 2026. Cosmos grows well when direct sown, as it doesn't transplant well or germinates quickly outdoors.