đź“Ś Quick Reference

🔵 Database: Blue & Blue-Adjacent Flowering Plants

Plant Name Genus/Species True Blue? Bloom Season Sun Needs Water Needs Annual/Perennial Height Notes
Cosmos (Pink) Cosmos bipinnatus ❌ No Summer–Fall Full sun Low–moderate Annual 2–4 ft Most common cosmos color
Cosmos (Purple) Cosmos bipinnatus ❌ No (closest to blue) Summer–Fall Full sun Low–moderate Annual 2–4 ft Can look bluish in low light
Cosmos (Orange) Cosmos sulphureus ❌ No Summer–Fall Full sun Low–moderate Annual 1–3 ft Heat-tolerant
Cosmos (Yellow) Cosmos sulphureus ❌ No Summer–Fall Full sun Low–moderate Annual 1–3 ft Bright, seasonal
Delphinium Delphinium spp. ✅ Yes Early–Mid Summer Full sun–partial Moderate–high Perennial 3–6 ft True vivid blue spires; toxic if ingested
Lobelia Lobelia erinus ✅ Yes Spring–Fall Partial–full sun Moderate Annual 4–8 in Great for borders/hanging baskets
Salvia (Blue) Salvia farinacea ✅ Yes Summer–Fall Full sun Low–moderate Perennial/Annual 1–3 ft Attracts pollinators
Hydrangea (Blue) Hydrangea macrophylla ✅ Yes (pH-dependent) Summer Partial shade High Perennial (shrub) 3–6 ft Blue only in acidic soil (pH <6)
Cornflower Centaurea cyanus ✅ Yes Late Spring–Summer Full sun Low Annual 1–3 ft Classic true-blue wildflower
Morning Glory Ipomoea tricolor ✅ Yes Summer–Fall Full sun Moderate Annual (vine) 6–10 ft (vine) Fast-growing climber
Himalayan Blue Poppy Meconopsis betonicifolia ✅ Yes Late Spring Partial shade High Perennial 3–4 ft Difficult to grow; cool climates only
Forget-Me-Not Myosotis scorpioides ✅ Yes Spring Partial shade High Biennial/Perennial 6–12 in Naturalizes in moist soil
Bachelor's Button Centaurea cyanus ✅ Yes Summer Full sun Low Annual 1–2.5 ft Same species as Cornflower
Balloon Flower Platycodon grandiflorus ✅ Yes Summer Full sun–partial Moderate Perennial 1–2.5 ft Buds inflate like balloons before opening
Blue Star (Amsonia) Amsonia tabernaemontana ✅ Yes Late Spring Full sun–partial Low–moderate Perennial 2–3 ft Great fall foliage color too
Siberian Iris Iris sibirica ✅ Yes Late Spring–Summer Full sun–partial Moderate–high Perennial 2–4 ft Tolerates wet soil
Chicory Cichorium intybus ✅ Yes Summer Full sun Low Perennial (short-lived) 1–4 ft Roadside wildflower, edible root
Blue Salvia (Meadow Sage) Salvia pratensis ✅ Yes Late Spring–Summer Full sun Low Perennial 1.5–3 ft Drought-tolerant
Nigella (Love-in-a-Mist) Nigella damascena ✅ Yes Summer Full sun Low–moderate Annual 1–2 ft Ornamental seed pods after bloom
Plumbago Plumbago auriculata ✅ Yes Summer–Fall Full sun Low–moderate Perennial (shrub) 3–6 ft Frost-tender, warm-climate favorite
Agapanthus (Blue) Agapanthus africanus ✅ Yes Summer Full sun Moderate Perennial 2–4 ft Bold globe-shaped flower clusters

âť“ FAQ / Troubleshooting

Q: Is blue cosmos a real cultivar I can buy seeds for? A: No. Any "blue cosmos" seed listing is either mislabeled, digitally altered in photos, or refers to a dyed/painted flower — not a genetic trait.

Q: My purple cosmos looks blue in photos — is that normal? A: Yes. Purple cosmos petals can appear blue-shifted under certain lighting or camera white balance, especially in shade or overcast light.

Q: Which plant on this list is easiest for beginners who want true blue? A: Cornflower and Lobelia — both are low-maintenance annuals with high germination rates and tolerate average soil.

Q: Why won't my cosmos flower? A: Usually excessive fertilizer or insufficient sun. Reduce feeding and ensure 6+ hours of direct light.

Q: Can I turn my hydrangea blue on purpose? A: Yes — lower soil pH below 6.0 using soil acidifier or aluminum sulfate; blue coloring is pH-dependent, not genetic in the same way as delphinium or cornflower.

Data compiled from and expanded on this guide: Blue Cosmos Flower: Facts, Colors & Meaning