You can sow several annual flower seeds outdoors in summer, including zinnias, cosmos, sunflowers, marigolds, calendula, bachelor’s buttons and nasturtiums. The right choice depends on your local frost dates, soil warmth and how much growing time remains: late-spring sowings can provide summer flowers, while midsummer sowings are a shorter-window bet for late-season color.
Which flower seeds can you plant in summer?
For a late-spring sowing intended to bloom through summer, UMass Amherst Extension recommends sowing calendula, cosmos, bachelor’s button, nasturtium, sunflower and zinnia in prepared soil in late May in its regional context. Iowa State University Extension and Outreach also lists bachelor’s button, cosmos, marigold, nasturtium, sunflower and zinnia among annuals that can be direct-seeded.
Those recommendations are useful starting points, not a single calendar for every climate. Check your seed packet for the variety’s sowing window, days to bloom, light and moisture needs, mature height and spacing. Choose flowers suited to your intended use—such as a border, container or cut flowers—and whether the species is a good candidate for direct sowing.
Good candidates for late-spring sowing
- Zinnias: Listed by both UMass Amherst and Iowa State as a summer-sowing or direct-sowing option.
- Cosmos: Recommended for prepared-soil sowing by UMass Amherst and listed as direct-sowable by Iowa State. Iowa State reports 5–7 days to germination under its table conditions; that is not the time to flowering.
- Sunflowers: Included in UMass Amherst’s late-May recommendations and Iowa State’s direct-sow list. Iowa State’s germination table reports 5–7 days to germination and flags sunflower as a species that does not transplant well.
- Marigolds: Iowa State lists marigold among annuals that can be direct-seeded.
- Calendula, bachelor’s button and nasturtium: UMass Amherst recommends these for late-May sowing; Iowa State also lists bachelor’s button and nasturtium as direct-sowable. Nasturtium is flagged by Iowa State as a species that does not transplant well.
Is it too late to sow flower seeds?
Not necessarily. For midsummer sowing, look for varieties with a short interval from germination to bloom that can keep flowering as days shorten. In a 2024 response to a July–August sowing question from Hamilton County, Ohio (Zone 6b), Ask Extension expert Deborah recommended that approach and cited 65–70 days to bloom for Cosmos sulphureus ‘Diablo’ and 60–70 days for dwarf French marigolds. She said zinnias might also work and suggested trying some seeds in trays and others directly in the garden under the local heat conditions. These are regional examples, not guarantees for every variety or location.
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To judge your own window, compare the packet’s days-to-bloom information with the time remaining before your first expected frost, and account for local temperatures and conditions. Days to germination are not days to flowering: for example, Iowa State’s 5–7-day cosmos and zinnia figures describe germination under its table conditions, not when flowers will appear.
When should you sow seeds outdoors?
There is no universal summer sowing date. Use your local frost calendar, soil warmth and the time remaining before frost. For warm-weather annuals, Virginia Cooperative Extension advises generally waiting until after the last frost; its guidance says most such seeds do not germinate well when soil is below 60°F. Treat that as Virginia Extension’s source-specific guidance, not a universal threshold for every species or climate.
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Regional examples illustrate why timing needs to be localized: UMass Amherst’s late-May recommendation addresses its regional context, while the Ohio Zone 6b response concerns July–August sowing for late-season flowers. Elsewhere, follow your local planting calendar and the instructions for the specific variety.
How to direct-sow flower seeds
- Prepare the bed. Make a fine, weed-free seedbed with good seed-to-soil contact. Iowa State recommends working and raking the annual-flower bed to remove large clods.
- Sow at the packet’s depth. Seed-covering needs differ by species; some seeds need light to germinate. Follow the packet rather than applying one depth to every flower.
- Maintain moisture. Keep the seedbed moist while seeds germinate, then thin seedlings to the recommended spacing.
- Watch for surface crusting. Virginia Cooperative Extension describes how a crusted soil surface can keep water from reaching outdoor-sown seeds. Its suggested technique is to sow in furrows filled with vermiculite and water with a fine mist; this is one optional method, not a universal requirement.
Should you sow directly or start seeds indoors?
Direct sowing skips the indoor seedling and transplant stages and suits species that do not transplant well, including sunflower and nasturtium in Iowa State’s guidance. The trade-off is timing: Iowa State cautions that most annuals sown directly in the garden will flower later than those started indoors and transplanted.
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Indoor starting can bring earlier flowers for many annuals, but it requires containers, growing medium, suitable light, moisture and temperature. For a late sowing, the Ohio Extension response’s suggestion to split seeds between trays and the garden offers a practical way to compare methods under your own conditions without assuming one will work everywhere.
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