March is a useful indoor-sowing window for several annual flowers, but it is not a universal planting date—and seeds started now will often flower later, after seedlings are planted outside. Choose by counting back from your local, frost-safe planting date and following the seed packet, rather than sowing every variety on the same day.
How to decide what to sow in March
“Annuals are plants that complete their life cycle in one growing season,” according to the Royal Horticultural Society. For starting seeds, the important date is when young plants can safely go outdoors—not simply the first day of March.
Extension schedules use different reference points. Purdue University Extension gives many flower sowing times as weeks before the last frost; Iowa State University Extension and Outreach describes how long seedlings generally need from sowing until they are ready to plant outside. The University of Missouri Extension calendar is approximate for mid-Missouri (Zone 5), with adjustments needed farther north or south. Minnesota and Indiana schedules likewise reflect local conditions, not a single calendar for every gardener.
- Estimate your local last-frost date and intended planting-out date. Use local guidance for your area.
- Count back the recommended indoor lead time for each flower below. Treat the cited schedule as a starting point, not a guarantee.
- Check the packet for germination light, temperature, covering, and moisture requirements before sowing.
- Plant seedlings outdoors only when local conditions are suitable; harden them off as directed by your local extension service or seed supplier.
Seven annual flowers to start indoors
These are seven defensible March candidates, not a prescription to sow all of them on one date. Their schedules vary by region and source.
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1. Snapdragon (Antirrhinum majus)
Snapdragons need a relatively long indoor start. Purdue recommends sowing nine weeks before the last frost; Missouri lists early March for mid-Missouri. Iowa State gives eight to ten weeks from sowing to planting out and a germination range of seven to fourteen days. Missouri notes that snapdragon seeds need light to germinate and that seedlings grow best in cool conditions. Follow your packet’s sowing depth and local schedule. Purdue University Extension; University of Missouri Extension; Iowa State University Extension and Outreach.
2. Dianthus or pinks
The University of Minnesota Extension includes dianthus in its mid-March indoor schedule, at about nine weeks before planting out. Missouri lists early March for mid-Missouri and advises covering the seeds lightly and growing seedlings in cool conditions. Local timing may differ. University of Minnesota Extension; University of Missouri Extension.
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3. Salvia (scarlet sage)
Minnesota’s schedule puts scarlet sage, or salvia, in mid-March, about nine weeks before planting out. Missouri lists mid-March and notes that salvia seeds need light to germinate. Check the packet before covering the seeds. University of Minnesota Extension; University of Missouri Extension.
4. Statice (Limonium sinuatum)
Minnesota Extension places statice in its mid-March schedule, about nine weeks before planting out; Purdue’s general schedule gives eight weeks before last frost. Use the lead time that matches your intended outdoor date and regional guidance. University of Minnesota Extension; Purdue University Extension.
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5. Nicotiana (flowering tobacco)
Minnesota lists nicotiana for mid-March, about nine weeks before planting out. Missouri’s mid-Missouri calendar places it in late March and notes that the seeds need light to germinate. Since the schedules differ, use your local planting date and packet instructions rather than treating either date as universal. University of Minnesota Extension; University of Missouri Extension.
6. Ageratum
Minnesota’s early-March schedule gives ageratum a longer indoor lead time of ten to eleven weeks before planting out. Purdue recommends sowing it nine weeks before the last frost. Plan from the date seedlings can move outside in your area. University of Minnesota Extension; Purdue University Extension.
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7. Annual phlox
Minnesota includes annual phlox in its mid-March schedule, about nine weeks before planting out. Missouri lists late March and advises direct seeding into containers. If using containers, sow according to the packet and avoid disturbing the seedlings when moving them. University of Minnesota Extension; University of Missouri Extension.
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Use clean containers and seed-starting mix, and provide adequate light after germination. The University of Minnesota Extension recommends seed-starting mix and says to follow seed-packet or catalog directions. Requirements vary: some seeds need light to germinate, while others should be covered. Iowa State’s germination guide explains that light and temperature needs differ by species, so do not assume one sowing depth or growing condition suits all seven.
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When direct sowing may be better
Most annual flowers are best sown outdoors after frost danger has passed and the soil has warmed, according to Iowa State’s guidance on direct seeding annuals. Some cool-season annuals, including nasturtium, can be sown three to four weeks before the last frost. Direct sowing can also suit flowers that are difficult to transplant. Iowa State notes that nasturtium and zinnia do not transplant well; if starting either indoors, peat pots can reduce disturbance. For other candidates, choose between indoor starts and direct sowing based on their transplant tolerance and your local conditions.
Why some familiar annuals are not on this March list
Calendula, French marigold, nasturtium, cosmos, and zinnia can be good choices for later spring sowing or direct seeding, but their timing does not make them universal early- or mid-March indoor starts. Minnesota lists calendula and French marigold in early April, and cosmos and zinnia in mid-April. Purdue places marigold, cosmos, and zinnia at six weeks before last frost. Use those later schedules where they fit your climate, rather than moving them earlier just to fill a March tray.
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