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.
To learn more about the various flowers available for your garden, make sure to check out our list of “Flower Names A to Z”.
25 Appealing Flowers That Start With O
1. 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
- 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)
- 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
- 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
- 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)
- 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
- 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
- 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
- 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
This beautiful flower can really light up a garden, but we warned it is highly poisonous.
10. Ophrys (Bee Orchid)
- 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)
- 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)
- 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
This flower is perfect for those looking for a backyard orchard-themed garden.
13. 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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)
- 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
- 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
- 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)
- 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)
- 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
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