From sunflowers and nasturtiums to zinnias and celosia, there are so many beautiful flower seeds that you can plant in May. With the right preparation, you can have your garden bursting with vibrant blooms all summer. Let’s look through some of our top picks for flowering plants to sow from seed this month.
1. Sunflower
Sunflowers are a quick and easy flower to plant from seed in May. The soil outdoors is warm enough for fast germination, and the plants will have time to grow strong before summer heat sets in. And no matter the size of the plant you choose, sunflowers are easy to grow and loved by pollinators.
Sunflower seeds typically sprout in 7–10 days, and most varieties bloom about 70–100 days after planting. That means seeds sown in May usually produce flowers by mid to late summer. For best results, choose a sunny spot with well-drained soil, remove weeds, and plant seeds ½ inch deep. Space them about 6–12 inches apart, depending on how large the variety grows.
Sunflowers come in a wide range of sizes. Dwarf varieties like ‘Suntastic,’ ‘Music Box,’ and ‘Teddy Bear’ stay under 3 feet tall and are great for containers or front borders. Medium-height types like ‘Autumn Beauty’ or ‘Lemon Queen’ grow 4–6 feet tall and work well in most garden beds. Tall varieties like ‘Mammoth’ or ‘American Giant’ can easily reach 8–12 feet or more. These taller cultivars often need staking or wind protection and make striking focal points in the garden.
2. Nasturtium
Nasturtium is an easy-to-grow annual flower that’s easy to plant from seed in May. The soil is warm enough for seeds to sprout quickly, usually within 7–14 days. Most nasturtium varieties bloom about 35–60 days after planting, so seeds sown in May will typically start flowering by early to mid-summer.
Choose a sunny spot with well-draining soil. Avoid over-fertilizing, as nitrogen-rich soil encourages leaf growth at the expense of flowers. Plant the seeds ½ inch deep and space them 8–12 inches apart for compact varieties or up to 18 inches for trailing types.
Nasturtiums come in both bush and trailing forms. Compact cultivars like ‘Tom Thumb’ stay under 12 inches tall and are ideal for borders or containers. Mounding varieties like ‘Empress of India’ grow 12–16 inches tall with a bushy habit and rich dark foliage. Trailing and climbing types such as ‘Jewel of Africa’ or ‘Alaska’ can spread 3–6 feet and look great spilling from hanging baskets or climbing up trellises. All types produce bright, edible flowers in shades of red, orange, yellow, and cream.
3. Zinnia
Zinnias are ideal to plant from seed in May after the last spring frost. Zinnia seeds usually germinate within 5–10 days and begin to bloom about 60–70 days after planting. That means seeds sown in early May often start flowering by mid to late July. Zinnias bloom heavily until the first fall frost, especially if deadheaded regularly.
Choose a full sun location for best results (the most flowers per plant). Plant zinnia seeds ¼ inch deep in well-draining soil and space them 6–12 inches apart depending on the variety.
Zinnias vary widely in size and form. Compact varieties like ‘Profusion’ stay around 12–18 inches tall and are great for borders or containers. Medium-sized types like ‘Zahara’ grow 12–24 inches tall and have strong disease resistance. Tall cultivars such as ‘Benary’s Giant’ can reach 3–4 feet and produce large, dahlia-like blooms perfect for cutting.
4. Celosia
Celosia seeds need warm soil to germinate (typically above 60°F (16°C)). Celosia seeds germinate in 5–15 days in warm weather and usually bloom about 60–90 days after sowing. That means May plantings often begin flowering in July or August. These plants thrive in hot weather, tolerate drought once established, and work well in both gardens and cut flower arrangements.
Celosia comes in three main types: plume (Celosia plumosa), cockscomb (Celosia cristata), and wheat-type (Celosia spicata). Dwarf plume varieties like ‘Fresh Look Red’ stay around 12 inches tall and are good for edging beds. Mid-sized types like ‘Dragon’s Breath’ grow about 20–24 inches and produce vibrant, feathery plumes. Cockscomb varieties such as ‘Chief Mix’ can reach 2–3 feet with large, crinkled blooms.
5. Cosmos
Cosmos seeds germinate quickly once the soil warms to at least about 60°F (16°C). Sow seeds directly into well-drained garden soil in full sun. They usually germinate within 7–10 days and begin blooming about 60–90 days after planting. This means cosmos seeds planted in May often start flowering by late July or early August. For a longer bloom season, sow seeds every 2–3 weeks through to early summer.
Cosmos plants grow with tall, airy stems and fern-like leaves. They branch freely and bloom heavily, attracting pollinators throughout the season. Popular tall varieties like ‘Sensation Mix’ and ‘Double Click’ grow 3–5 feet tall and work well at the back of flower beds. Dwarf types such as ‘Sonata’ and ‘Cosmic Orange’ stay around 12–24 inches tall and are good for borders or containers.
All cosmos varieties prefer lean soil and minimal fertilization for best flowering. Deadheading spent blooms can help extend the blooming season.
6. Nigella
Nigella, also known as love-in-a-mist, is a popular annual flower typically planted in mid-spring. Nigella does not transplant well, so direct seeding is best. It also self-seeds easily, so you may see volunteer plants next season if you leave some seed pods in place.
Sow seeds directly into well-drained soil in full sun. Gently press them into the surface, as they need light to germinate. Seeds typically sprout in 10–14 days, and flowers bloom around 65–80 days after planting. If you plant in mid-May, you can expect blooms by late July or early August. Nigella prefers cooler weather, so late spring sowing is best in cooler climates.
Nigella grows in a soft, bushy mound with feathery leaves and delicate flowers that almost seem to float. Most varieties grow 12–24 inches tall and form dense clusters. Popular cultivars include ‘Miss Jekyll’ with light blue blooms and ‘Persian Jewels’, which features shades of pink, white, and lavender. The seed pods are ornamental and often used in dried arrangements.
7. Sweet peas
Sweet peas are an old-fashioned favorite that can be planted in May in cooler climates or regions where spring has arrived late. While they prefer to be sown in early spring or even late winter, May plantings can still succeed with careful timing and proper site selection.
Sow the seeds directly into rich, well-drained soil in a sunny location, spacing them about 1 inch deep and 2–3 inches apart. Germination usually takes 10–21 days, and blooms appear approximately 10–12 weeks after planting. That means May-sown sweet peas typically start blooming by mid to late summer.
Sweet peas need support to grow well. They can reach 4–8 feet tall, depending on the cultivar and growing conditions. Dwarf bush types like ‘Knee High Mix’ or ‘Explorer’ stay under 2 feet and are great for containers. Popular smaller cultivars like ‘Cupani’ and ‘Old Spice’ are known for their strong fragrance and compact growth. Others, such as ‘Spencer’ types, produce large, ruffled blooms on long stems, ideal for cutting.
8. Chamomile
Chamomile seeds can be planted when soil has warmed in the spring. Choose a sunny spot with well-drained soil, and scatter the seeds on the surface, pressing them in gently without covering them too much. Chamomile seeds need light to germinate. Keep the soil moist until germination, which typically takes 7–14 days. Blooms usually appear about 6–10 weeks after planting, meaning May sowings will begin flowering by mid to late summer.
Chamomile reaches about 8–24 inches tall depending on the type. German chamomile (Matricaria chamomilla) is an annual that grows up to 2 feet tall and is widely used for tea. It tends to self-seed readily. Roman chamomile (Chamaemelum nobile) is a perennial ground cover that grows about 6–12 inches tall and spreads horizontally.
Popular cultivars include ‘Bodegold’ for German chamomile (known for high oil content and upright growth) and ‘Treneague’ for Roman chamomile (a non-flowering, low-maintenance lawn alternative). Both types produce daisy-like flowers with white petals and yellow centers that attract pollinators and lend a soft, wild look to the garden.
9. Marigold
Marigolds are easy to plant in May once the soil has warmed and frost risk is gone. They typically germinate within 5–7 days when sown directly into the garden. Sow seeds about 1 inch apart and cover lightly with soil. Expect blooms to appear 45–60 days after planting, which means you’ll likely see your first flowers in late June or early July.
Marigolds thrive in full sun and well-drained soil, and they’re often used in borders, vegetable beds, and containers for both color and pest deterrence. They come in three main types with different growth habits and sizes.
- African marigolds (Tagetes erecta) are the tallest, growing 2–3 feet high with large, globe-like blooms. ‘Crackerjack’ and ‘Inca II’ are popular cultivars.
- French marigolds (Tagetes patula) are more compact at 6–12 inches tall and are ideal for edging. ‘Bonanza’ and ‘Safari’ are common choices.
- Signet marigolds (Tagetes tenuifolia) like ‘Lemon Gem’ and ‘Tangerine Gem’ are fine-leaved, mound-forming plants that reach about 10–12 inches and are known for their edible, citrus-scented blooms.
10. Bachelor’s button
Bachelor’s button, also known as cornflower, is an easy-to-grow annual that can be planted from seed in May, especially in cooler regions or where earlier sowings weren’t possible. These seeds germinate best in soil temperatures between 60°F and 70°F.
After sowing, expect seedlings to emerge within 7–10 days. Bloom time is generally about 60–80 days after planting, depending on the weather and cultivar.
For best results, sow seeds about 1/4 inch deep in a sunny, well-drained spot and thin seedlings to about 6 inches apart once they sprout.
Bachelor’s buttons have an upright, branching habit and grow between 12–36 inches tall, depending on the variety. Popular cultivars include ‘Blue Boy’ (classic bright blue, 24–30 inches tall), ‘Black Ball’ (deep burgundy, 24 inches), and ‘Polka Dot Mix’ (a colorful blend of blues, pinks, whites, and purples, about 16 inches tall).
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