Complete Gardening
Timing is everything in the garden, especially when starting perennials from seed. May stands as that crucial turning point when some perennial varieties still eagerly sprout while others have missed their ideal window. Understanding which seeds still have potential and which should wait until fall can save you frustration and garden space. Let’s explore which perennial seeds you can successfully start now and which ones you should hold off on until cooler weather returns.
1. Blanket Flower (Gaillardia) – Heat-tolerant and fast to flower
Gardeners adore Blanket Flowers for their resilience in hot, dry conditions. These prairie natives sprout quickly in warm soil, often showing their first true leaves within just 10-14 days.
The cheerful daisy-like blooms in fiery red, orange, and yellow combinations attract butterflies while shrugging off summer heat waves. Even first-year seedlings typically flower by late summer when started in May.
Plant seeds just 1/8 inch deep in well-draining soil, keeping them consistently moist until germination. Once established, these drought-tolerant beauties need minimal care while providing years of reliable color.
2. Black-eyed Susan (Rudbeckia) – Prefers warm soil; blooms by midsummer
Golden sunshine on stems! Black-eyed Susans thrive when sown in May’s warming soil. Their cheerful yellow petals surrounding dark centers create instant summer cheer in any garden space.
Unlike fussier perennials, Rudbeckia seeds germinate readily without special treatment, typically emerging in just 7-14 days. First-year flowering is common when started now, with blooms continuing well into fall frost.
Simply scatter seeds on prepared soil and barely cover them – they need light to germinate. Water gently but consistently until seedlings establish. These native prairie flowers develop drought tolerance quickly, making them perfect for low-maintenance gardens.
3. Coneflower (Echinacea) – Germinates in 7–21 days, flowers late summer
Native prairie champions, Echinacea seeds respond beautifully to May’s warming temperatures. Their distinctive cone-shaped centers surrounded by downward-drooping petals make them garden standouts.
May-sown seeds typically germinate within three weeks when kept consistently moist. The seedlings grow steadily through summer, often producing their first blooms by season’s end – an unexpected bonus for first-year perennials!
Beyond their beauty, Echinacea brings medicinal value and crucial pollinator support to your garden. Plant seeds just 1/4 inch deep in well-draining soil where they’ll receive at least 6 hours of sunlight daily for best results.
4. Coreopsis – Bright, daisy-like blooms just weeks after sowing
Sunshine in plant form! Coreopsis ranks among the fastest perennials from seed to bloom, often flowering within 8-10 weeks of May planting. The cheerful yellow, orange, or bicolor blooms seem to float above delicate, lacy foliage.
These easy-going plants germinate readily in warm soil without fussy requirements. Simply press seeds lightly into prepared soil – they need some light to sprout effectively.
First-year flowering makes Coreopsis instantly rewarding for impatient gardeners. Their drought tolerance once established and ability to thrive in poor soils makes them perfect for beginning gardeners. Deadhead spent blooms to encourage continuous flowering all season long.
5. Shasta Daisy (Leucanthemum × superbum) – Easy germination and early bloom
Classic white daisies bring timeless charm to any garden, and May offers the perfect window to start them from seed. Their crisp white petals surrounding golden centers emerge from some of the easiest perennial seeds to germinate.
Sprinkle seeds on moistened soil and barely cover them – they need light to sprout. Germination typically occurs within 10-14 days at warm temperatures.
Many seedlings produce their first blooms by late summer when started in May. The plants form attractive rosettes of glossy green leaves before sending up sturdy stems loaded with flowers. Their long vase life makes them excellent cutting garden additions that return reliably year after year.
6. Phlox (Phlox paniculata) – Sow now for fragrant midsummer color
Fragrant clouds of color await gardeners who sow Phlox seeds in May. Unlike many perennials that delay flowering until their second year, these sweetly scented beauties often produce their first blooms by late summer when started now.
Garden phlox seeds benefit from the naturally warming soil temperatures of late spring. They typically germinate within 14-21 days when kept consistently moist.
Butterfly magnets extraordinaire, these native North American flowers produce dome-shaped clusters of tiny star-shaped blooms in pink, purple, white, or bicolor patterns. Plant in an area with good air circulation to prevent powdery mildew issues as the plants mature into stunning garden centerpieces.
7. Salvia (Salvia nemorosa) – Fast-growing spikes of purple or pink
Architectural and drought-tolerant, Salvia creates vertical drama in gardens with minimal fuss. May planting gives these seeds the perfect germination conditions – they sprout readily in warm soil within 10-14 days.
The spiky flower stalks in shades of purple, blue, or pink attract beneficial insects while deterring deer and rabbits with their aromatic foliage. Many varieties bloom their first season when started in May, creating months of pollinator-friendly blooms.
Space seeds about 1/4 inch deep in well-draining soil. Once established, these Mediterranean natives thrive with minimal watering. Deadheading spent flower spikes often triggers a second flush of blooms, extending their garden performance well into fall.
8. Yarrow (Achillea millefolium) – Hardy seedling, blooms in 8–10 weeks
Ancient healing herb meets modern garden workhorse in yarrow’s fern-like foliage and flat-topped flower clusters. These tough-as-nails perennials germinate rapidly in May’s warming soil, often sprouting within a week.
Their drought tolerance once established makes them perfect for challenging garden spots. The feathery foliage forms attractive mounds before sending up sturdy stems topped with flowers in white, yellow, pink, or red.
First-year blooming often occurs when started in May, providing instant garden gratification. Simply press seeds lightly into soil – they need some light to germinate effectively. Native yarrow varieties support beneficial insects while naturalizing beautifully in meadow gardens.
9. Campanula (Campanula carpatica) – Bellflowers appear by midsummer
Charming bell-shaped blooms make Campanula carpatica a cottage garden favorite. May-sown seeds germinate readily in 14-21 days when kept consistently moist, forming neat mounds of foliage.
Unlike taller Campanula varieties, these compact bellflowers grow just 8-10 inches tall, making them perfect for garden edges or container planting. The upward-facing blue or white bells appear surprisingly quickly, often flowering their first season when started in May.
Sprinkle seeds on moistened soil and barely cover them – they need light to germinate effectively. Their long blooming period from summer through fall provides continuous garden interest. Deadheading spent flowers encourages reblooming throughout the growing season.
10. Gaura (Gaura lindheimeri) – Whirling white blossoms in 60–75 days
Dancing butterflies seem to hover above the garden when Gaura blooms. These airy, wand-like stems covered in delicate white or pink flowers create movement and lightness in perennial borders.
May sowing provides ideal germination conditions – seeds typically sprout within 14-21 days when kept consistently moist. The plants grow quickly, often producing their first ethereal blooms within just 60-75 days of planting.
Native to American prairies, Gaura develops exceptional drought tolerance once established. Plant seeds 1/4 inch deep in well-draining soil where they’ll receive full sun. Their wispy nature makes them perfect for interplanting with more structural perennials for a naturalistic garden effect.
11. Sedum (Sedum spectabile) – Fleshy leaves, late-summer flower heads
Succulent foliage meets pollinator paradise in Sedum spectabile. These drought-resistant plants germinate readily in May’s warming soil, forming rosettes of fleshy leaves that store water like living reservoirs.
The flat-topped flower clusters in shades of pink or mauve appear by late summer, attracting countless butterflies and bees. Even in their first season, May-sown seedlings often produce modest blooms.
Sprinkle seeds on well-draining soil and barely cover – they need light to germinate effectively. Their ability to thrive in poor soil makes them perfect for problematic garden spots. As autumn approaches, the flower heads mature into attractive seed heads that provide winter interest and food for birds.
12. Bee Balm (Monarda didyma) – Sow in warm soil for hummingbird magnet by August
Native American healing plant turned garden superstar, Bee Balm creates spectacular whorls of spiky tubular flowers in red, pink, or purple. May sowing capitalizes on warming soil temperatures these seeds love, typically germinating within 10-14 days.
The fragrant, mint-family foliage forms bushy clumps before sending up flower stems by late summer. Hummingbirds find these nectar-rich blooms irresistible, often visiting repeatedly throughout the day.
Scatter seeds on prepared soil and barely cover – they need some light for effective germination. Provide good air circulation to prevent powdery mildew issues. Even first-year plants often produce modest blooms when started in May, with spectacular flowering in subsequent seasons.
1. Delphinium – Requires cool germination and fall stratification
Towering blue spires make Delphinium garden royalty, but May planting spells disappointment. These cool-weather lovers need specific conditions to break dormancy – namely extended cold periods followed by gradual warming.
When started in May’s warmth, seeds either fail to germinate or produce weak, spindly seedlings prone to flopping. The natural cycle for Delphinium involves seeds ripening in summer, falling to earth, and experiencing winter’s chill before spring germination.
Save these seeds for September planting in pots kept outdoors through winter, or refrigerate them for 2-3 weeks before February indoor starting. Patience brings reward – properly stratified seeds produce those magnificent 4-6 foot flower spikes that define English cottage gardens.
2. Lupine (Lupinus polyphyllus) – Best sown in fall for strong spring seedlings
Those magnificent spires of pea-like flowers in rainbow hues require winter’s touch to break dormancy effectively. May-planted Lupine seeds struggle with their hard seed coats intact, resulting in spotty germination and weak growth.
Wild lupines naturally drop seeds in summer that remain dormant until winter freezes crack their protective coatings. This cold stratification process triggers spring’s explosion of color.
For best results, sow lupine seeds directly outdoors in October-November where they’ll experience natural winter conditions. Alternatively, nick the seed coat with a file and refrigerate for 4-6 weeks before February indoor starting. Your patience yields those spectacular flower spikes that grace cottage gardens in late spring.
3. Foxglove (Digitalis purpurea) – Biennial; seed in autumn for spring flowering
Stately spires of spotted, tubular bells make foxgloves woodland garden stars, but their biennial nature demands specific timing. May planting leads to stunted growth and delayed flowering by an entire year.
These woodland natives follow a distinct two-year cycle: first forming rosettes of fuzzy leaves, then flowering spectacularly in their second spring before setting seed and dying. Fall sowing mimics their natural cycle, allowing seedlings to establish before winter dormancy.
Save these seeds for August-September planting either in pots or directly in the garden. The resulting rosettes will overwinter successfully before producing those magnificent 3-5 foot flower spikes that attract bumblebees and create cottage garden magic the following spring.
4. Columbine (Aquilegia vulgaris) – Prefers a cool period—autumn sowing ideal
Dancing fairy-like blooms on delicate stems make columbines spring garden treasures, but May planting leads to germination frustration. These woodland natives evolved to drop seeds in summer that require winter’s cold touch to wake up properly.
May-sown seeds typically sit dormant or germinate sporadically and weakly. Their natural cycle includes a period of cold stratification that breaks internal dormancy mechanisms.
Mark your calendar for September-October sowing either in pots kept outdoors through winter or directly in the garden. This timing allows seeds to experience natural temperature fluctuations that trigger robust spring germination. Your patience rewards you with those distinctive spurred flowers that attract hummingbirds and early pollinators.
5. Primrose (Primula vulgaris) – Needs winter chilling for reliable germination
Early spring’s cheerful harbingers, primroses bring woodland charm with their clusters of yellow, pink, or purple blooms. Unfortunately, May planting works against their natural germination requirements – these seeds need extended cold periods to break dormancy.
In nature, primrose seeds ripen in early summer, fall to the ground, and remain dormant until winter’s chill triggers spring germination. This cold stratification process is essential for reliable sprouting.
Save these seeds for autumn sowing in pots kept outdoors through winter, or refrigerate them for 4-6 weeks before February indoor starting. Your reward comes in those early spring clusters of bright blooms when the garden awakens from winter’s sleep.
6. Oriental Poppy (Papaver orientale) – Sow in autumn for robust spring growth
Those spectacular dinner-plate sized blooms in vibrant orange, red, or pink require nature’s timing, not May planting. Oriental poppy seeds need extended cold periods to break dormancy effectively – a process completely bypassed with late spring sowing.
In their natural cycle, seeds ripen in early summer, scatter, and remain dormant until fall rains and winter chilling prepare them for spring germination. This cold stratification breaks internal dormancy mechanisms.
Mark your calendar for September-October sowing either directly in the garden or in pots kept outdoors through winter. The resulting seedlings develop strong tap roots before dormancy, enabling those spectacular spring blooms that stop garden visitors in their tracks.
7. Sweet William (Dianthus barbatus) – Biennial seed needs fall sow to bloom next year
Clusters of fragrant, fringed flowers make Sweet William cottage garden classics, but their biennial nature requires specific timing. May planting results in poor germination and delays flowering by an entire year.
These old-fashioned favorites follow a distinct two-year cycle: forming leafy rosettes their first year, then producing flower clusters in their second spring before setting seed and dying. Fall sowing aligns with their natural cycle.
Save these seeds for August-September planting either in pots or directly in the garden. The resulting rosettes establish strong root systems before winter dormancy, then burst into those spectacular clove-scented bloom clusters the following May-June. Their sweet fragrance and butterfly appeal make the wait worthwhile.
8. Meadow Rue (Thalictrum aquilegiifolium) – Fall sowing gives best spring emergence
Airy clouds of tiny lavender blooms dancing atop tall stems make Meadow Rue garden aristocracy, but May planting leads to dormancy issues. These woodland natives evolved to drop seeds in summer that require winter’s cold touch to germinate effectively.
The natural cycle includes extended cold stratification that breaks internal dormancy mechanisms. Without this cold period, seeds either fail to sprout or germinate sporadically and weakly.
Plan for September-October sowing either in pots kept outdoors through winter or directly in the garden. This timing allows seeds to experience natural temperature fluctuations that trigger robust spring germination. Your patience yields those ethereal flower plumes that bring height and movement to partly shaded garden areas.
9. Canterbury Bells (Campanula medium) – Fall seed ensures spring flowers
Gorgeous bell-shaped blooms in blue, pink, or white make Canterbury Bells garden showstoppers, but their biennial nature demands specific timing. May planting pushes flowering back by an entire year.
Unlike their perennial Campanula cousins, Canterbury Bells follow a strict two-year life cycle: forming rosettes their first year, then producing magnificent flowering stalks in their second spring before setting seed and dying. Fall sowing aligns perfectly with this natural rhythm.
Save these seeds for August-September planting either in pots or directly in the garden. The resulting rosettes establish strong root systems before winter dormancy, then transform into those spectacular 2-3 foot flower spikes the following summer. Their classic cottage garden appeal makes them worth the wait.
10. Pasque Flower (Pulsatilla vulgaris) – Requires cold stratification over winter
Silky, cup-shaped blooms followed by feathery seed heads make Pasque Flowers early spring treasures, but May planting works against their natural germination requirements. These alpine natives evolved to drop seeds in early summer that remain dormant until winter’s chill triggers spring germination.
The name “Pasque” references Easter, highlighting their very early bloom time after winter dormancy. This emergence pattern requires seeds to experience extended cold periods to break internal dormancy.
Plan for September-October sowing either in pots kept outdoors through winter or directly in the garden. Alternatively, refrigerate seeds for 4-6 weeks before February indoor starting. Your patience yields those beautiful purple, white, or red blooms that open while snow still lingers in garden corners.
11. Aster (Symphyotrichum spp.) – Autumn sow leads to sturdier clumps
Late-season stars with their daisy-like blooms in purple, pink, or white, asters provide crucial fall pollinator support. While some varieties tolerate May sowing, most perform significantly better with autumn planting.
Native asters evolved to drop seeds in fall that experience winter’s cold before spring germination. This natural cold stratification process results in stronger seedlings with better branching habits.
For best results, sow aster seeds in September-October either directly in the garden or in pots kept outdoors through winter. The resulting seedlings develop robust root systems their first season, producing fuller flower displays in subsequent autumns. Their late-season color and pollinator value make them garden essentials worth planting properly.
12. Bleeding Heart (Dicentra spectabilis) – Needs cool, moist conditions to germinate
Romantic heart-shaped blooms dangling from arching stems make Bleeding Hearts woodland garden treasures, but May planting leads to germination failure. These shade-lovers evolved to drop seeds in early summer that require multiple cold-warm cycles to break complex dormancy.
In nature, bleeding heart seeds experience summer warmth, fall moisture, winter cold, and spring warming before germination. This complex stratification can’t be replicated with May planting.
Save these seeds for autumn sowing in pots kept outdoors through winter, or use specialized techniques involving refrigeration phases. Even with perfect timing, expect slow germination – often taking two years from seed to first bloom. The spectacular spring display of dangling pink or white hearts makes the extended process worthwhile.