25 Flowers That Start With The Letter O

Oh, what joy flowers bring to our gardens! If you’re looking for something interesting, look no further than flowers that start with O. From drought-loving cacti to delicate orchids, there’s sure to be something on this list that will suit your garden.

If you enjoy vegetable gardening, take a look at oriental onions and oregano, both of which grow beautiful flowers that will complement your veggies.

Keep reading to learn about these gorgeous flowers that start with O.

Flowers That Start With O

Quick Look

1. Obedient Plant

obedient plant

  • Scientific Name: Physostegia virginiana
  • Sun: Full sun, partial shade
  • Water: Keep soil moist and occasionally wet
  • Size: 3-4 feet (0.91-1 meters)
  • Lowest Temperature: -50°F (-45.5°C)
  • Toxicity: None
  • Colors: Pink, purple, lavender, white

2. Obovate Peony

obovate peony

  • Scientific Name: Paeonia obovata
  • Sun: Partial shade
  • Water: Keep soil moist
  • Size: 1-2 feet (30-60 centimeters)
  • Lowest Temperature: -20°F (-28°C)
  • Toxicity: None
  • Colors: Red, purple, white

3. Obregonia (Artichoke Cactus)

obregonia

  • Scientific Name: Obregonia denegrii
  • Sun: Partial shade
  • Water: Drought tolerant, keep soil dry
  • Size: Up to 6 inches (15 centimeters)
  • Lowest Temperature: 20°F (-6°C)
  • Toxicity: None
  • Colors: Pink, yellow, white

4. Ocean Pearls

ocean pearls

  • Scientific Name: Agrostemma githago
  • Sun: Full sun, partial shade
  • Water: Drought tolerant, keep soil moist
  • Size: Up to 3 feet (91 centimeters)
  • Lowest Temperature: -30°F (-34°C)
  • Toxicity: Low, only if seeds are eaten
  • Colors: Pink, purple, lavender

5. Oconee Bells

oconee bells

  • Scientific Name: Shortia galacifolia
  • Sun: Partial shade, deep shade
  • Water: Keep soil moist
  • Size: 4-6 inches (10-15 centimeters)
  • Lowest Temperature: -10°F (-23.3°C)
  • Toxicity: None
  • Colors: Pink, white

6. Oenothera (Evening Primrose)

oenothera

  • Scientific Name: Oenothera biennis
  • Sun: Full sun, partial shade
  • Water: Keep soil moist, somewhat drought tolerant
  • Size: 3-5 feet (0.91-1.5 meters)
  • Lowest Temperature: -30°F (-34°C)
  • Toxicity: None
  • Colors: Yellow, gold

7. Ohio Spiderwort

ohio spiderwort

  • Scientific Name: Tradescantia ohiensis
  • Sun: Full sun, partial shade, deep shade
  • Water: Keep soil moist, tolerant of drought and wet conditions
  • Size: 2-3 feet (60-91 centimeters)
  • Lowest Temperature: -30°F (-34°C)
  • Toxicity: None
  • Colors: Red, burgundy, blue, purple, lavender

This species may be listed as invasive in some areas.

8. Old Lady Cactus

old lady cactus

  • Scientific Name: Mammillaria hahniana
  • Sun: Partial sun
  • Water: Drought tolerant, keep soil dry
  • Size: Up to 10 inches (25 centimeters)
  • Lowest Temperature: -5°F (-20.5°C)
  • Toxicity: None
  • Colors: Pink

9. Oleander Plant

oleander plant

  • Scientific Name: Nerium oleander
  • Sun: Full sun, partial shade
  • Water: Drought tolerant, keep soil moist
  • Size: 6.5-19.5 feet (1.9-5.9 meters)
  • Lowest Temperature: 10°F (-12°C)
  • Toxicity: High, can be fatal if eaten
  • Colors: Pink, red, burgundy, orange, yellow, gold, purple, lavender, white, cream, tan

10. Ophrys (Bee Orchid)

ophrys

  • Scientific Name: Ophrys apifera
  • Sun: Partial shade
  • Water: Drought tolerant, keep soil moist
  • Size: 6-20 inches (15-50 centimeters)
  • Lowest Temperature: -10°F (-23.3°C)
  • Toxicity: None
  • Colors: Pink, yellow, green, brown

11. Opuntia (Prickly Pear Cactus)

opuntia

  • Scientific Name: Opuntia polyacantha
  • Sun: Full sun
  • Water: Drought tolerant, keep soil dry
  • Size: Up to 8 inches (20 centimeters)
  • Lowest Temperature: -40°F (-40°C)
  • Toxicity: Low, causes skin irritation
  • Colors: Pink, orange, yellow, gold

12. Orange Blossom (Navel Orange)

orange blossom

  • Scientific Name: Citrus x sinensis
  • Sun: Full sun
  • Water: Keep soil moist
  • Size: Up to 30 feet (9.1 meters)
  • Lowest Temperature: 20°F (-6°C)
  • Toxicity: Low, fruit skin and plant material may cause skin irritation
  • Colors: White

13. Orange Coneflower

orange coneflower

  • Scientific Name: Echinacea “Tiki Torch”
  • Sun: Full sun, partial shade
  • Water: Drought tolerant, keep soil moist
  • Size: 2-3 feet (60-91 centimeters)
  • Lowest Temperature: -40°F (-40°C)
  • Toxicity: None
  • Colors: Orange

14. Orange Daylily

orange daylily

  • Scientific Name: Hemerocallis fulva
  • Sun: Full sun, partial shade
  • Water: Keep soil moist
  • Size: 3-6 feet (0.91-1.8 meters)
  • Lowest Temperature: -40°F (-40°C)
  • Toxicity: Toxic to cats
  • Colors: Orange

15. Orange Stonecrop

orange stonecrop

  • Scientific Name: Phedimus kamtschaticus
  • Sun: Full sun
  • Water: Drought tolerant, keep soil dry
  • Size: Up to 6 inches 15 centimeters)
  • Lowest Temperature: -40°F (-40°C)
  • Toxicity: Low
  • Colors: Pink, red, burgundy, orange, yellow, gold, purple, lavender, white

16. Orchid

orchid

  • Scientific Name: Phalaenopsis
  • Sun: Dappled sunlight, deep shade
  • Water: Keep soil moist
  • Size: 9-36 inches (22-91 centimeters)
  • Lowest Temperature: 30°F (-1.1°C)
  • Toxicity: None
  • Colors: Pink, green, purple, lavender, white

17. Oregon Grape

oregon grape

  • Scientific Name: Berberis aquifolium, Mahonia aquifolium
  • Sun: Full sun, partial shade
  • Water: Keep soil moist
  • Size: 3-10 feet (0.91-3 meters)
  • Lowest Temperature: -20°F (-28°C)
  • Toxicity: None
  • Colors: Yellow, gold

18. Orienpet Lily

orienpet lily

  • Scientific Name: Lilium “Scheherazade”
  • Sun: Full sun, partial shade
  • Water: Keep soil moist
  • Size: 4-7 feet (1-2.1 meters)
  • Lowest Temperature: -30°F (-34°C)
  • Toxicity: None
  • Colors: Red, yellow, white

19. Oriental Lily

oriental lily

  • Scientific Name: Lilium x “Double Beauty”
  • Sun: Full sun, partial shade
  • Water: Keep soil moist
  • Size: 2-3 feet (60-91 centimeters)
  • Lowest Temperature: -20°F (-28°C)
  • Toxicity: None
  • Colors: Pink, white

20. Oriental Poppy

oriental poppy

  • Scientific Name: Papaver orientale
  • Sun: Full sun, partial shade, dappled sunlight
  • Water: Drought tolerant, keep soil moist
  • Size: 2-3 feet (60-91 centimeters)
  • Lowest Temperature: -40°F (-40°C)
  • Toxicity: Low
  • Colors: Pink, red, burgundy, orange, purple, lavender, white, black

21. Orlaya (White Lace Flower)

orlaya

  • Scientific Name: Orlaya grandiflora
  • Sun: Full sun, partial shade
  • Water: Keep soil moist
  • Size: 2-3 feet (60-91 centimeters)
  • Lowest Temperature: -50°F (-45.5°C)
  • Toxicity: None
  • Colors: White

22. Ornamental Onion

ornamental onion

  • Scientific Name: Allium “Gladiator”
  • Sun: Full sun, partial shade
  • Water: Drought tolerant, keep soil dry
  • Size: 3-4 feet (0.91-1 meters)
  • Lowest Temperature: -30°F (-34°C)
  • Toxicity: None
  • Colors: Purple

Allium “Gladiator” may become weedy and hard to control. Some locations where they're invasive may ban them completely.

23. Ornamental Oregano

ornamental oregano

  • Scientific Name: Origanum vulgare
  • Sun: Full sun
  • Water: Drought tolerant, keep soil moist
  • Size: 1-3 feet (30-91 centimeters)
  • Lowest Temperature: -30°F (-34°C)
  • Toxicity: None
  • Colors: Pink, purple, white

24. Ornithogalum (Cape Hyacinth)

ornithogalum

  • Scientific Name: Orinthogalum
  • Sun: Full sun, partial shade
  • Water: Keep soil moist
  • Size: 1-3 feet (30-91 centimeters)
  • Lowest Temperature: -30°F (-34°C)
  • Toxicity: None
  • Colors: Green, white

25. Osteospermum (African Daisy)

osteospermum

  • Scientific Name: Osteospermum
  • Sun: Full sun
  • Water: Keep soil moist
  • Size: 8-24 inches (20-60 centimeters)
  • Lowest Temperature: 30°F (-1.1°C)
  • Toxicity: None
  • Colors: Purple, lavender, white