What to Plant in August: Best Flowers & Seeds for Late Summer Gardens
August might feel like the tail end of summer, but for savvy gardeners it's one of the most strategic planting months of the year. The right seeds started now will reward you with vibrant color through September, October, and beyond — and set you up for a spectacular fall garden. Whether you're filling gaps in your beds, starting seeds indoors for fall transplants, or direct-sowing fast-maturing annuals, this guide covers exactly what to plant in August and why.
At Trailing Petunia, we specialize in premium pelleted and raw flower seeds chosen for performance, color, and reliability. Everything featured below is available in our shop — and every variety has been selected because it genuinely thrives when started in August.
Why August Is a Great Month to Plant Seeds
Most gardeners think of spring as the only seed-starting season, but August opens a second window that experienced growers take full advantage of. Soil temperatures are warm, days are still long enough to fuel germination, and many annuals started now will bloom right through the first frost. You're also getting ahead of the fall rush — plants started in August hit their stride just as summer-fatigued gardens need a refresh.
The key is choosing varieties with shorter days-to-bloom and good heat or cool tolerance depending on your climate zone. The six varieties below are our top picks for August planting.
6 Best Flowers to Plant in August
1. Zinnia Seeds — Crestar Mix
Zinnias are the quintessential August flower. Fast-maturing, heat-loving, and absolutely prolific, they go from seed to bloom in as little as 60 days. The Crestar Mix is a premium cut flower zinnia with large, fully double blooms in a rich palette of reds, oranges, pinks, and creams. Direct sow into warm soil now and you'll have armloads of cut flowers by late September.
👉 Shop Zinnia Crestar Mix Seeds — 100 Seeds
2. Marigold Seeds — Endurance™ Sunset Gold Triploid
Marigolds are one of the most reliable August-to-frost performers in any garden. The Endurance™ Sunset Gold Triploid is a standout African marigold — massive golden blooms on compact, well-branched plants that don't set seed, so they just keep flowering. Start seeds indoors now for transplants in 3–4 weeks, or direct sow in warmer zones.
👉 Shop Marigold Endurance™ Sunset Gold Seeds — 25 Seeds
3. Sunflower Seeds — Always Sunny Gold
Think it's too late for sunflowers? Not with a fast-maturing dwarf variety. Always Sunny Gold is a compact, multi-branching sunflower that produces a succession of cheerful golden blooms on manageable plants — perfect for containers, borders, or cutting gardens. Direct sow in August for blooms in 55–65 days.
👉 Shop Always Sunny Gold Sunflower Seeds — 15 Seeds
4. Pentas Seeds — Honey Cluster Red
Pentas is an underrated gem for late summer planting. These star-shaped clusters of flowers are heat-tolerant, drought-resistant, and absolutely beloved by butterflies and hummingbirds. Honey Cluster Red is a vivid, compact variety that thrives in containers and garden beds alike. Start seeds indoors in August for transplants ready to go out in 4–6 weeks.
👉 Shop Honey Cluster Red Pentas Seeds — 25 Pelleted Seeds
5. Nicotiana Seeds — Starmaker Mix
Nicotiana — flowering tobacco — is one of the most fragrant annuals you can grow, and it's surprisingly easy from seed. The Starmaker Mix produces compact, upright plants covered in star-shaped blooms in shades of white, pink, red, and lime green. Start indoors in August for transplants that will bloom right through fall. The evening fragrance alone is worth it.
👉 Shop Starmaker Mix Nicotiana Seeds — 25–100 Pelleted Seeds
6. Gerbera Daisy Seeds — Royal Deep Pink Dark Eye
Gerbera daisies are a premium cut flower that also make stunning container plants. The Royal Deep Pink Dark Eye variety features bold, jewel-toned blooms with a dramatic dark center — a real showstopper. Start seeds indoors in August for plants that will bloom in fall and can even be overwintered indoors in colder climates.
👉 Shop Gerbera Daisy Royal Deep Pink Dark Eye Seeds — 15 Seeds
Shop Now — August Planting Picks
Ready to get planting? Here are all six August favorites in one place:
Browse our full late summer seed collection: Trailing Petunia — All Flower Seeds
August Planting Tips by Region
Zones 3–5 (Northern US, Canada)
August is your last reliable window for direct-sowing fast annuals like zinnias and sunflowers. Focus on varieties with 55–65 day maturity. For everything else — marigolds, pentas, nicotiana, gerbera — start indoors now and keep plants in containers you can bring inside if an early frost threatens.
Zones 6–7 (Mid-Atlantic, Pacific Northwest, Midwest)
You have a comfortable window for both direct sowing and indoor starts. Zinnias and marigolds can go straight into the ground. Start pentas, nicotiana, and gerbera indoors for transplants in 4–6 weeks. Expect blooms well into October.
Zones 8–10 (South, Southwest, California)
August is prime time. The heat suits zinnias, marigolds, pentas, and sunflowers perfectly. You can also begin starting cool-season flowers like pansies and violas indoors now for fall planting — they'll be ready to go out when temperatures drop in September and October.
August Seed Starting: Indoors vs. Direct Sow
Knowing whether to start seeds indoors or direct sow is half the battle in August. Here's a quick breakdown for the varieties above:
- Direct sow outdoors: Zinnias, Sunflowers, Marigolds (warmer zones)
- Start indoors for transplants: Pentas, Nicotiana, Gerbera Daisy, Marigolds (cooler zones)
- Either works: Marigolds in zones 6–8
For indoor starts, use a quality seed-starting mix, maintain soil temps of 70–75°F, and provide 14–16 hours of light daily under grow lights. Pelleted seeds (like our pentas, nicotiana, and gerbera) make spacing and handling much easier — especially for small seeds.
Related Growing Guides
Want to go deeper on any of these flowers? We have full growing guides for many of our most popular varieties:
- African Marigold Seeds Growing Guide | Giant Marigold Flowers
- French Marigold Seeds Growing Guide | Compact Garden Marigolds
- Impatiens Seeds: The Complete Growing & Buying Guide
- Vinca Seeds: Complete Growing Guide for Endless Summer Color
- The Ultimate Guide to Growing Lobelia Seeds
- Start Dahlias from Seeds — Easy Growing Guide
Frequently Asked Questions: Planting in August
Is it too late to plant flower seeds in August?
No — August is actually an excellent time to plant many annuals. Fast-maturing varieties like zinnias, marigolds, and sunflowers can go from seed to bloom in 55–70 days, giving you color well into fall. In warmer zones (8–10), August is one of the best months to plant.
What flowers grow fastest from seed in August?
Zinnias are the fastest, often blooming in 55–60 days from direct sow. Marigolds and sunflowers are close behind at 60–70 days. For indoor starts, pentas and nicotiana typically reach transplant size in 4–6 weeks.
Can I start seeds indoors in August?
Absolutely. Starting seeds indoors in August is a great strategy for extending your season. Pentas, nicotiana, gerbera daisies, and even cool-season flowers like pansies and violas can all be started indoors now for fall transplanting.
What should I plant in August for fall color?
For fall color, focus on marigolds, zinnias, pentas, and nicotiana — all of which bloom prolifically right up to frost. In cooler zones, gerbera daisies started indoors now will bloom in fall and can be brought inside before frost to continue blooming.
Do I need pelleted seeds for August planting?
Pelleted seeds aren't required, but they make a real difference for small-seeded varieties like pentas, nicotiana, and gerbera. The clay coating makes seeds easier to handle, space accurately, and sow at the right depth — which improves germination rates, especially in warm August conditions.
What's the best way to water seeds started in August?
Keep soil consistently moist but not waterlogged. In August heat, outdoor direct-sown seeds may need watering twice daily until germination. For indoor starts, bottom-watering (setting trays in water and letting soil absorb from below) is ideal — it keeps the surface from drying out and reduces damping-off risk.
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