7 Annual Seeds to Start in March for Spring Flowers

Sunflowers

Few things make a garden more cheery than a brightly colored, oversized sunflower (Helianthus annuus) that chases those golden rays all day long. Best of all, they come in a variety of shapes, sizes, and hues—including yellow, orange, brown, and red—which means they’re adaptable to any garden. 

“They are garden wonders, adding a lot of drama since the flower head can grow to 6-inches to 2-feet wide,” says Madeline Hooper, gardening expert and host of the PBS show Garden Fit. “A big bonus is that their seeds can be harvested by drying the flower heads. They need soaking, salting, and baking, but the reward is you produce very tasty and healthy snacks.” 

Growing Tips: They can be started indoors or the seeds can be directly sown outdoors when there is no danger of another frost. In either case, it takes about 70 to 100 days for them to reach maturity. Hooper adds, “To ensure their stability in the garden, I add a strong tall sturdy stake to hold up their large flower heads next to the seedlings as soon as they are almost a foot tall.” 

• Hardiness Zone: USDA zones 2-11
• Light: Full sun
• Water: Keep seedlings moist; tolerates drought once established, but regular watering is ideal
• Soil: Neutral, acidic, or alkaline; well-draining

Zinnia

These easy-to-grow annuals are great to start early as seedlings indoors because they produce long-lasting blooms once sprouted. Available in basically every color of the rainbow, you can choose a specific hue or opt for a mix. (Many seed packets offer color blends for a dazzling show). 

“The vibrant colors of zinnias (Zinnia elegans) burst forth while their ability to thrive in sunlight makes them my favorite plants to grow,” says Tammy Sons, horticulturist and founder of TN Nursery in Altamont, Tennessee. 

Growing Tips: These hardy annual plants bloom in roughly 60 days which makes them ideal for an instant burst of spring color. “When cool weather persists, I begin growing them indoors but move them outdoors once the warmth becomes dependable,” Sons says. They thrive in full sun and well-drained soil, making them a favorite for summer flower beds, cutting gardens, and pollinator-friendly landscapes. 

• Hardiness Zone: USDA zones 2-11
• Light: Full sun
• Water: Keep seedlings moist; tolerates drought once established but regular watering is ideal
• Soil: Neutral, acidic, or alkaline; well-draining

Snapdragons

With their peculiar-shaped blooms, tall stalks, and splashy colors, snapdragons (Antirrhinum majus) are a great way to add some whimsy to your spring garden. These cool-season bloomers thrive when started early and can handle light frosts, making them perfect for an early start.  

Snapdragons are unique in that their blooms open from the bottom of the stalk upward, providing a long-lasting display of color. Their velvety petals also do a great job of attracting local pollinators like bees, butterflies, and hummingbirds, ushering even more life into your yard. 

Growing Tips: Snapdragons can be started indoors about 8 to 10 weeks before the last frost for an early-season display, or sown directly outdoors in cooler climates. They prefer full sun and well-drained soil, thriving in temperatures between 60 and 75°F. To encourage bushier growth and more blooms, pinch back the tips of young plants once they have a few sets of leaves.

• Hardiness Zone: USDA zones 7-11
• Light: Full sun to partial shade
• Water: Keep seedlings moist; water weekly during dry periods once established
• Soil: Neutral; moist and well-draining

Nasturtium

Nasturtiums (Tropaeolum majus) are fast-growing, trailing, or bushy annuals known for their vibrant, edible flowers and round, lily pad-like leaves. Given their vining habit, Hooper says that a single plant is usually enough for a garden.

“These plants have a wonderful way of covering the ground with profuse leafy vines that suppress weeds while they enchant you with their beautiful blooms that are also edible,” Hooper says. She adds, “They’re also great to garnish dishes and [to add a] super peppery taste in salads.” 

Growing Tips: Hooper recommends directly sowing nasturtium into the ground after the last frost. “The seeds benefit from soaking in water overnight, and then planted in well-drained soil,” she says. “They should be topped with a half inch of soil, and they’ll want direct sunlight.” Once the seedlings emerge, thin them out so they are spaced by at least a foot apart. 

• Hardiness Zone: USDA zones 9-11
• Light: Full sun to partial shade
• Water: Keep seedlings moist; water weekly during dry periods once established
• Soil: Neutral, acidic, or alkaline; moist and well-draining

Marigold

This hardy golden annual remains a garden staple for a reason—they’re easy to grow, low-maintenance, are resistant to pests, and come in a cheery assortment of yellow, orange, and red. Sons says marigolds (Tagetes patula) are especially great as a bordering plant in flower or vegetable beds to repel insects. 

Growing Tips: Start marigold seeds indoors four to six weeks before the last expected frost, or sow directly outdoors after any danger of frost has passed. “They reach full bloom between 60 to 70 days and display adaptability by growing successfully in numerous climate zones,” says Sons. “I plant them in soil that drains well, and carefully control watering which promotes their healthy growth.”

• Hardiness Zone: USDA zones 2-11
• Light: Full sun
• Water: Keep seedlings moist; water weekly during dry periods once established
• Soil: Slightly acidic to neutral; moist and well-draining

Bluemink

Bluemink (Ageratum houstonianum) is an annual flower that grows low to the ground and produces soft, fuzzy clusters of blue or purple flowers. You can get a jumpstart on them now by starting seeds indoors or sowing them as soon as the soil warms up, and their blooms will last through the summer and fall. 

“I love to have flowers in my garden I can cut for indoor arranging, and Ageratums are a perfect choice because, if you keep deadheading them, they will produce flowers all summer long,” Hooper says. “Another strong attribute is the range of blue colors and sizes they now come in. There are  more than 60 different cultivars to choose from.” 

Growing Tips: Hooper recommends starting these indoors so that, by the time of the last frost, you have substantial seedlings to add to the garden. They need eight to 10 weeks of growth indoors. “Bluemink likes sunlight but will tolerate some shade, and I tend to add garden stakes, such as dried ends of branches that have multiple arms of support so they can grow through them,” she adds. “In the right conditions they grow 6 to 12 inches wide on one stem, so I want assurance they stay upright to show off their blooms all season.” 

• Hardiness Zone: USDA zones 2-11
• Light: Full sun to partial shade
• Water: Keep seedlings moist; tolerates drought once established, but regular watering is ideal
• Soil: Neutral; moist and well-draining

Cosmos

This tall and feathery annual produces delicate, daisy-like blooms in pink, white, magenta, and red. Cosmos (Cosmos bipinnatus) have a sort of wildflower-like charm to them, making them a great option for cottage gardens, pollinator-friendly spaces, and areas where you want to add a bit of whimsy. 

“These plants give a tranquil appearance which complements any garden while thriving across different environmental conditions,” Sons adds. They tend to thrive even in less-than-ideal conditions and require little maintenance, making them a great choice for those who want a low-maintenance annual. 

Growing Tips: You can start cosmos seeds indoors four to six weeks before the last frost. Alternatively, Sons likes to sow seeds directly outdoors after the last frost in sunny locations to promote vigorous plant development. They’ll start producing flowers about 70 to 80 days later. They prefer full sun and well-drained soil, growing quickly and often self-seeding for blooms year after year. 

• Hardiness Zone: USDA zones 2-11
• Light: Full sun
• Water: Keep seedlings moist; tolerates drought once established
• Soil: Alkaline to neutral; well-draining