Flowers to Plant in Centennial, CO
Centennial’s zone 6a offers one of the longest and most versatile flower-growing seasons in the country. Your moderate climate supports an exceptionally wide range of flowers — cold-hardy perennials that also tolerate summer heat, spring bulbs that get the winter chill they need, and warm-season annuals that thrive from June through October. The key advantage of gardening in Centennial is that you can grow flowers from almost every category: spring-blooming bulbs, classic cottage garden perennials, heat-loving summer annuals, and fall bloomers that extend color well into November. With proper planning, continuous bloom from March through Thanksgiving is entirely achievable.
Spring Flowers for Centennial
Best spring-blooming flowers for USDA zone 6a
In moderate zones, tulips bloom 2–3 weeks earlier than in cold climates and offer an even longer season when you layer early, mid, and late cultivars. Species tulips like Tulipa clusiana return more reliably year after year than large-flowered hybrids.
10–24 inches · full sun · Spring
Tip: Plant in November after soil cools below 55°F. In zone 7, pre-chill large hybrid tulip bulbs for 6–8 weeks in the refrigerator (away from fruit) before planting for the best show.
Virginia Bluebells are a native woodland wildflower that carpets the forest floor with nodding blue bells in early spring. They are one of the finest native plants for naturalizing in shade gardens.
12–24 inches · part shade · Spring
Tip: Plant in moist, humus-rich soil under deciduous trees. They go dormant by midsummer, so interplant with ferns, hostas, or astilbe to fill the void. Mark their location so you don’t accidentally dig them up.
Perennial salvia is a drought-tolerant, deer-resistant workhorse that blooms for months. The upright flower spikes attract hummingbirds and butterflies while requiring almost no maintenance beyond occasional shearing.
18–24 inches · full sun · Spring to Summer
Tip: Plant in full sun with lean, well-drained soil. Shear spent flower spikes back by one-third after the first flush to trigger a strong rebloom. 'May Night' and 'Caradonna' are top cultivars for moderate zones.
Creeping Phlox transforms slopes, rock walls, and border edges into cascading sheets of color each spring. Its evergreen, needle-like foliage provides year-round ground cover.
4–6 inches · full sun · Spring
Tip: Plant in spring or fall in well-drained soil. After flowering, shear back by half to promote dense, compact growth and prevent the center from dying out. Space plants 12–18 inches apart for full coverage within 2 years.
Bearded Iris produces some of the most elegant and fragrant flowers in the spring garden, with an astonishing range of color combinations. Their sword-like foliage adds vertical structure to borders even when not in bloom.
24–40 inches · full sun · Spring
Tip: Plant rhizomes in late summer with the top of the rhizome exposed to the sun—burying them too deep invites rot. Divide clumps every 3–4 years after blooming to maintain vigor and prevent iris borer damage.
Summer Flowers for Centennial
Heat-tolerant flowers that thrive in zone 6a summers
Butterfly Weed is a native milkweed essential for monarch butterfly reproduction—it is the only food source for monarch caterpillars. Its brilliant orange flower clusters also attract a wide array of beneficial pollinators.
18–24 inches · full sun · Summer
Tip: Plant in full sun with very well-drained soil; it thrives in poor, sandy conditions and rots in clay. Has a deep taproot and resents transplanting, so choose your spot carefully. Emerges very late in spring—mark its location.
Coneflowers are native prairie plants that perform beautifully in moderate zones with minimal care. They bloom for months, attract butterflies and bees, and their seed heads feed goldfinches through winter.
24–48 inches · full sun · Summer
Tip: Plant in spring or fall in average, well-drained soil. Avoid overly rich soil or excessive mulch around the crown, which can lead to rot. The straight species is more reliable than many fancy hybrid cultivars.
Zinnias provide an explosion of color from midsummer through frost with almost no effort. In moderate zones they enjoy a longer season than in cold climates, often blooming well into October.
12–48 inches · full sun · Summer
Tip: Direct sow after last frost when soil reaches 70°F. For continuous bloom, make succession sowings every 2–3 weeks through early July. Water at the base to prevent powdery mildew on foliage.
Hydrangeas are the queens of the summer shade garden, producing enormous flower heads that last for months. In moderate zones, bigleaf hydrangeas reliably bloom on old wood without the winter die-back that plagues colder regions.
3–6 feet · part shade · Summer
Tip: Plant in morning sun with afternoon shade. Flower color depends on soil pH: acidic soil (below 5.5) produces blue flowers; alkaline soil (above 6.5) produces pink. Amend soil with aluminum sulfate for blue or lime for pink.
'Goldsturm' is the gold standard of reliable perennials, forming tidy clumps that erupt with golden daisies from midsummer through fall. It is tough, long-blooming, and adapts to a wide range of soils.
24–30 inches · full sun · Summer to Fall
Tip: Plant in spring or fall in average soil. It spreads by short runners but is not aggressive. Divide every 3–4 years when clumps become crowded. Pairs perfectly with purple asters for a classic late-summer combination.
Fall Flowers for Centennial
Flowers that extend your garden color into autumn
Garden Mums are a fall staple, providing dense mounds of long-lasting color for borders, containers, and entryways. In moderate zones they overwinter more reliably than in colder areas.
12–24 inches · full sun · Fall
Tip: For perennial performance, plant in spring rather than fall. Pinch tips through mid-July for the bushiest plants. Provide winter mulch after the ground freezes to prevent heaving.
Sasanqua camellias bloom from October through December, filling the garden with color when little else is flowering. They are more cold-hardy than japonica types and have a graceful, open habit.
6–10 feet · part shade · Fall to Early Winter
Tip: Plant in acidic, well-drained soil (pH 5.5–6.5) in part shade protected from cold winter winds. Mulch heavily but keep mulch away from the trunk. Choose cold-hardy cultivars like 'Yuletide' or 'Winter’s Star' for zone 6.
Aromatic aster is a native wildflower that forms tidy, dense mounds smothered in blue-purple daisy flowers throughout fall. It is drought tolerant, deer resistant, and thrives in lean soils.
18–24 inches · full sun · Fall
Tip: Plant in full sun with well-drained soil—it actually performs better in poor soil than rich. Cut back by half in June for a more compact habit. 'October Skies' is a top cultivar for garden use.
Winter Interest for Centennial
Flowers and plants that provide color and structure through winter
Hellebores begin blooming in January in moderate zones, providing flowers when the garden is at its barest. Their evergreen foliage and long-lasting blooms make them essential for winter shade gardens.
12–18 inches · part shade · Late Winter
Tip: Plant in rich, well-drained soil in part shade. Remove old, tattered foliage in late December to showcase winter blooms. Mulch with leaf mold or compost. They self-sow gently, creating lovely naturalized colonies.
Winter Jasmine produces bright yellow flowers on bare green stems from January through March, adding unexpected color to the dormant winter landscape. It is tough, adaptable, and virtually pest-free.
6–10 feet (spreading) · full sun · Winter
Tip: Train on a wall, fence, or let it cascade over a retaining wall. It roots where stems touch the ground, which can be useful for erosion control or a nuisance if not managed. Prune hard after flowering to keep it tidy.
Best Perennials for Centennial
Perennials that return year after year in zone 6a
Russian Sage creates an airy, silvery-blue haze in the garden from midsummer through fall. It is extremely drought tolerant, deer resistant, and thrives in the heat and humidity of moderate zones.
36–48 inches · full sun · Summer to Fall
Tip: Plant in full sun with lean, well-drained soil—rich soil causes floppy growth. Cut back to 6–12 inches in early spring as new buds appear on the woody stems. Do not cut back in fall as the stems provide winter interest.
Catmint is one of the longest-blooming perennials available, producing soft lavender-blue spikes from late spring through fall if sheared after each flush. Its aromatic foliage repels deer and rabbits.
12–18 inches · full sun · Spring to Fall
Tip: Plant in full sun with well-drained soil. Shear back by two-thirds after the first flush of bloom for a fresh mound of flowers in 2–3 weeks. 'Walker’s Low' is the industry standard cultivar for borders.
Must-Plant Bulbs for Centennial
Essential bulbs for zone 6a gardens
Camassia is an underused native bulb that thrives in moist meadow conditions where many other bulbs fail. Its tall spikes of starry blue flowers are a magnet for bees and add a wildflower charm to the garden.
24–36 inches · full sun · Late Spring
Tip: Plant bulbs 4–6 inches deep in fall in moist, heavy soil—unlike most bulbs, Camassia actually prefers clay. It naturalizes slowly but reliably in meadow plantings and along stream banks.
Monthly Planting Calendar for Centennial
Zone 6a flower planting schedule \u2014 Moderate (Zones 6–7)
| Month | What to Plant | What's Blooming | Key Tasks |
|---|---|---|---|
| January | Force branches of forsythia and quince indoors | Hellebore, Winter Jasmine | Order seeds and plan garden layout; Prune dormant deciduous trees and shrubs; Apply dormant oil spray to fruit trees and roses |
| February | Start seeds indoors under grow lights; Plant bare-root roses on mild days | Hellebore, Crocus (late month), Winter Jasmine | Cut back ornamental grasses before new growth; Prune roses on Washington’s Birthday (traditional timing); Begin removing winter mulch as soil warms |
| March | Direct sow sweet peas and larkspur; Set out pansies and violas | Crocus, Daffodil, Virginia Bluebells (late), Creeping Phlox (late) | Divide summer and fall perennials as they emerge; Apply pre-emergent herbicide to flower beds if desired; Top-dress beds with compost |
| April | Plant perennials and shrubs; Set out cool-season annuals | Tulip, Daffodil, Virginia Bluebells, Creeping Phlox, Iris (late) | Stake tall perennials (peonies, delphiniums); Begin regular fertilizing schedule; Monitor for aphids and treat with insecticidal soap |
| May(now) | Plant warm-season annuals after last frost; Direct sow zinnias and sunflowers | Iris, Salvia, Peony, Allium, Camassia | Mulch beds with 2–3 inches of organic mulch; Deadhead spent spring bulb flowers (leave foliage); Begin pinching mums for fall bloom |
| June | Succession sow zinnias; Plant tropical bulbs (cannas, dahlias) | Butterfly Weed, Coneflower, Hydrangea, Daylily, Salvia | Shear catmint and salvia after first bloom for rebloom; Water deeply once per week during dry spells; Scout for Japanese beetles and handpick or trap |
| July | Sow biennials (foxglove, hollyhock) for next year | Zinnia, Coneflower, Black-Eyed Susan, Hydrangea, Russian Sage (begins) | Stop pinching mums by mid-July; Deadhead annuals and perennials regularly; Water containers daily in hot weather |
| August | Divide and replant bearded irises; Order spring bulbs | Zinnia, Black-Eyed Susan, Russian Sage, Catmint (rebloom) | Take cuttings of tender perennials; Begin reducing fertilizer applications; Divide spring-blooming perennials |
| September | Plant spring bulbs; Plant perennials for fall root establishment | Garden Mum, Aster, Sedum, Goldenrod | Collect seeds from open-pollinated plants; Plant cover crops in empty annual beds; Begin fall garden cleanup of diseased material |
| October | Continue planting spring bulbs; Plant sasanqua camellias | Camellia sasanqua, Garden Mum, Aster | Dig tender bulbs (dahlias, cannas) after frost; Leave healthy perennial stems for winter interest; Apply 3–4 inches of mulch to new plantings |
| November | Finish planting spring bulbs; Plant bare-root shrubs | Camellia sasanqua, Hellebore (late month in mild years) | Protect borderline-hardy plants with extra mulch; Clean and store garden tools; Compost fallen leaves or shred for mulch |
| December | — | Camellia sasanqua (early), Hellebore (in mild winters) | Force paperwhites and amaryllis indoors; Plan next year’s garden and order catalogs; Inspect stored tender bulbs for rot or desiccation |
Common Flower Garden Mistakes in Centennial
Site hydrangeas where they receive morning sun and afternoon shade, especially in zone 7 where summer heat can scorch leaves and wilt blooms.
Large hybrid tulips need 10–12 weeks of cold below 45°F to bloom well. In zone 7, refrigerate bulbs before planting, or switch to species tulips that need less chilling.
Spring bloomers (azaleas, forsythia, camellias) set buds on old wood. Prune immediately after flowering, never in fall or winter, or you will remove next year’s buds.
Many flower problems blamed on watering or fertilizing are actually pH issues. Test soil every 2–3 years and amend to the 6.0–6.8 range for most flowers. Acid-loving plants need dedicated beds.
Soil & Pollinator Notes
Soil Notes for Zone 6a
Moderate-zone soils vary widely from heavy Piedmont clay to coastal sand. Amend clay soils with compost and coarse organic matter to improve drainage; amend sandy soils to increase moisture retention. Most garden flowers prefer a pH of 6.0–6.8. Hydrangeas and camellias need acidic soil (pH 5.0–5.5), so amend with sulfur or plant in dedicated beds.
Pollinator Notes
Moderate climates support pollinators from February through November—a much longer season than cold zones. Emphasize native plants like coneflower, butterfly weed, and asters that co-evolved with local bee and butterfly species. Avoid double-flowered cultivars that lack pollen and nectar.
Frequently Asked Questions
What are the best flowers to plant in Centennial, CO?
The best flowers for Centennial’s zone 6a (Moderate (Zones 6–7)) include spring bloomers like Tulip and Virginia Bluebells, summer favorites like Butterfly Weed and Coneflower, and reliable perennials like Russian Sage and Catmint. These varieties are matched to your climate and will thrive with proper care.
When should I plant flowers in Centennial?
In Centennial (zone 6a), spring bulbs go in the ground in fall. Spring and summer annuals should be planted after the last frost date. Perennials can be planted in spring or early fall. Check the monthly planting calendar above for specific timing by month.
What flowers bloom all summer in Centennial?
Long-blooming summer flowers for zone 6a include Butterfly Weed, Coneflower, Zinnia. Deadheading spent blooms and consistent watering will keep these flowering from June through September or later.
What perennials come back every year in Centennial?
Top returning perennials for Centennial’s zone 6a include Russian Sage, Catmint. These are hardy in your zone and will return larger and stronger each year once established.
What bulbs should I plant in Centennial?
The best bulbs for Centennial include Camassia. Plant bulbs 4–6 inches deep in fall in moist, heavy soil—unlike most bulbs, Camassia actually prefers clay. It naturalizes slowly but reliably in meadow plantings and along stream banks.