Organic Gardening

11 Outrageous Flowers That Start With O + Growing Guides

Organizing the optimal garden is not just about getting ornamental flowers that ooze opulence. Rather, it is about observing the particular characteristics and needs of flowers and optimizing your garden to facilitate growth. 

Purple Ornamental Onion
Purple Ornamental Onion

Open up to your endless options when looking for flowers, starting with O. In this article, I cover the A to Z about planting these flowers and give you opportunities to enhance your gardening journey. 


1. Obedient Plant (Physostegia virginiana)

Obedient Plant
Pink flowering Obedient Plant

The obedient plant gets its name from its flexible stems. The soft stems can be bent into different positions and will retain that form permanently. This unique behavior has earned the plant its name, ‘obedient plant,’ as if it were obeying the gardeners’ directions. 

This tall pink perennial forms long tubular stems, often reaching 2 to 4 feet in length. They have long cones that are packed densely with buds that will bloom to reveal small trumpet-shaped flowers. These can be purple, pink, or white in color. 

Botanical Name:  Physostegia virginiana 
Growth Rate:  Moderate to fast 
Native Range:  North America 
Hardiness Zones: 3-9
Dangers: Non-toxic 
Soil Needs:  Moist to wet soil 
Exposure: Full sun to partial shade 
Ease of Care: Moderate 
Diseases: Rust, brown spot
Propagation: Seeds or division 
Fertilizer: None needed 
Pests: Spider mites, aphids, 
Blooming Period: Summer to early fall 
Pruning: Light pruning to manage the shape of growth 
Water needs: Moderate to high 
Obedient Plant Growing Guide Chart

2. Oregano (Origanum vulgare)

Oregano
Bee taking pollen from a purple flowering Oregano plant

Origanum vulgare is the common oregano herb used in cooking. While most people only know this as an herb, it actually makes for a fantastic garden plant. 

Not to mention, you also get a supply of extremely fragrant fresh oregano that adds some cheer and joy to your kitchen creations as well. Oregano is a sun-loving ground cover that will creep across your garden given enough time.

This is one of the oldest herbs used for culinary and medicinal purposes in the Mediterranean region for several centuries. Oregano is associated with joy, well-being, and positive energy — and is even used as a symbol of good luck. 

Botanical Name:  Origanum vulgare 
Growth Rate:  Moderate 
Native Range:  Mediterranean region
Hardiness Zones: 4-9
Dangers: None 
Soil Needs:  Well-drained soil, loam, sand 
Exposure: Full sun 
Ease of Care: Easy 
Diseases: Antracnose, damping off, verticillium wilt, powdery mildew, mint rust
Propagation: Seeds or cuttings 
Fertilizer: None needed 
Pests: Aphids, spider mites, leaf miners 
Blooming Period: Summer 
Pruning: Light pruning will encourage more growth 
Water needs: Moderate watering 
Oregano Growing Guide Chart

3. Oregon Grape (Mahonia)

Oregon Grape
Yellow clusters of flowers on the Oregon Grape plant

Mahonia is a beautiful little shrub with several benefits besides its unique look. This particular berry bush holds a special place in the hearts of Native Americans. 

Oregon grape has been used by Native Americans for centuries in various ways. It produces small grape-like berries, which are used to create dyes, and its roots are used for medicinal purposes. 

It features spiky, leathery leaves, and after the berries are gone, it will develop small yellow flowers that look amazing in contrast to the thick green leaves. 

The berries are also a favorite with wildlife, so be ready to accept some visitors. 

Botanical Name:  Mahonia 
Growth Rate:  Slow to moderate 
Native Range:  North America 
Hardiness Zones: 5-9
Dangers: Berries can be toxic to pets in large quantities 
Soil Needs:  Loam, sand, clay
Exposure: Full sun to shade 
Ease of Care: Easy to moderate 
Diseases: Pierce’s disease, fan-leaf virus 
Propagation: Seeds or stem cuttings 
Fertilizer: None needed 
Pests: Grapevine moth, vine mealybug 
Blooming Period: Spring 
Pruning: Prune after flowering to maintain shape 
Water needs: Moderate 
Oregon Grape Growing Guide Chart

4. Oyster Plant (Tradescantia Spathacea)

Oyster Plant
Oyster plant white flowers

The oyster plant is a great starter plant for new gardening enthusiasts. It is colorful, perennial with white flowers, extremely easy to maintain, and quite sturdy. 

This plant features long, lance-shaped leaves that are dark green on the upper side and purple/magenta underneath. The leaves tend to curl upwards, creating a boat-like shape. This exposes the colorful underside and creates an interesting texture. 

The oyster plant occasionally develops small white flowers that are nestled in the long leaves, which look like an oyster nestled in its shell. 

Botanical Name:  Tradescantia spathacea 
Growth Rate:  Moderate 
Native Range:  Mexico and Central America 
Hardiness Zones: 9-11
Dangers: The sap can be a skin irritant 
Soil Needs:  Well drained soil, sand
Exposure: Indirect light to partial shade 
Ease of Care: Easy 
Diseases: Root rot, leaf spot
Propagation: Stem cuttings or division 
Fertilizer: None 
Pests: Spider mites, mealybugs, caterpillars 
Blooming Period: Can occasionally develop flowers 
Pruning: None 
Water needs: Moderate 
Oyster plant Growing Guide Chart

5. Oriental Poppy (Papaver orientale)

Oriental Poppy
Orange Oriental Poppy flowers

The Oriental Poppy is a much larger version of the common poppy/California poppy flower. 

These orange perennial flowers can typically reach 6 inches in diameter. They have an interesting dark orange, nearly plastic-orange type of color and a dark brown and almost black center. 

There are many different kinds of poppy flowers, and they hold importance in many cultures and societies around the world. They are considered a sign of beauty and luxury and in the sphere of gardening, they are a prized asset to have in your garden. 

Botanical Name:  Papaver Orientale 
Growth Rate:  Moderate 
Native Range:  Eastern Mediterranean region
Hardiness Zones: 3-8
Dangers: The sap can irritate the skin 
Soil Needs:  Well drained soil 
Exposure: Full sun 
Ease of Care: Moderate 
Diseases: Powdery mildew, botrytis 
Propagation: Seeds or division 
Fertilizer: Apply a slow-release fertilizer in spring.
Pests: Aphids, slugs, snails
Blooming Period: Late spring to early summer 
Pruning: None 
Water needs: Moderate 
Oriental Poppy Growing Guide Chart

6. Ornamental Onion (Allium sp.)

Ornamental Onion
Tall purple Ornamental Onion flowers

The ornamental onion is a purple flowering perennial that has many different species. The Allium cultivar is especially popular due to its structure and color. 

This plant has been used as a gardening plant for many centuries. It features long, sturdy stems at the end of which you will find a fuzzy flower head. This spherical flower head consists of hundreds of tiny purple flowers. 

It can look like a pompom or woolen ball attached to the plant from a distance. These don’t have any special history to them other than the fact that they have been popular for hundreds of years due to their unique shape and colors. 

If you want to add a striking visual contrast to your garden, the ornamental onion will certainly do it. 

Botanical Name:  Allium Sp. 
Growth Rate:  Moderate 
Native Range:  Different species come from different places 
Hardiness Zones: 4-8
Dangers: Some species are toxic if ingested 
Soil Needs:  Loam, sand 
Exposure: Full sun 
Ease of Care: Easy to moderate 
Diseases: White rot, bulb rot, mildew, rust
Propagation: Bulbs or seeds 
Fertilizer: None 
Pests: Onion thrips, nematodes, bulb eelworm
Blooming Period: Late spring 
Pruning: Light pruning can help growth 
Water needs: Moderate 
Ornamental Onion Growing Guide Chart

7. Oxeye Daisy (Leucanthemum Vulgare)

Oxeye Daisy
Oxeye Daisy

The Oxeye Daisy is the classic daisy you’ll see in media and representations of daisy-filled fields nestled between lush green hills. This is a very common and popular plant in Europe and has played an important role in European culture. 

The daisy is seen as a sign of innocence, purity, and youth. It is an attractive flower that features white petals on the border and a warm yellow center cone. The petals are arranged in a radial layout, creating the unique look of the plant. 

The thin, delicate, lance-like leaves are very visually appealing. These flowers sit at the end of stems that can be up to 4 feet long, making them perfect for large and small spaces alike. 

Botanical Name:  Leucanthemum vulgare 
Growth Rate:  Fast 
Native Range:  Europe, Asia, North Africa 
Hardiness Zones: 3-8
Dangers: Non-toxic 
Soil Needs:  Well drained soil 
Exposure: Full sun to partial shade 
Ease of Care: Easy 
Diseases: Verticillium wilt, leaf spots 
Propagation: Seeds or division 
Fertilizer: None 
Pests: Aphids, mites, leaf miners 
Blooming Period: Summer 
Pruning: Light pruning will help denser growth 
Water needs: Moderate 
Oxeye Daisy Growing Guide Chart

8. Orchid (Orchidaceae)

Orchid
Pink spotted Orchid flower

The Orchidaceae is a diverse family of plants well known for their beautiful and often highly fragrant flowers. 

You can get flowers of all different shapes, sizes, and colors within this group of plants. The most common shape is a five-petal orchid. However, there are many other types as well. 

These are commonly found in many colors, such as white, pink, purple, yellow, blue, and more. 

There is plenty of variety when it comes to plant size. Some varieties can be used as table flowers, while others are vines that can easily spread up and across an entire wall or building. 

Orchids have been used for centuries as decorative plants in cultures around the world. 

Botanical Name:  Orchidaceae 
Growth Rate:  Can vary depending on the species 
Native Range:  Various species are found all over the world
Hardiness Zones: Varies depending on the species 
Dangers: Some species are toxic if ingested 
Soil Needs:  Orchid-specific potting mixture 
Exposure: Varies from filtered light to bright indirect light 
Ease of Care: Moderate to advanced 
Diseases: Southern blight, botrytis, powdery mildew 
Propagation: Division, baby plants and through division 
Fertilizer: Orchid-specific fertilizers 
Pests: Aphids, scale insects, spider mites, and others 
Blooming Period: Some bloom once a year while others bloom multiple times 
Pruning: Removing spent flowers will help with growth 
Water needs: Light watering but watering needs to be done carefully 
Orchid Growing Guide Chart

9. Orange Blossom (Citrus Sinensis)

Orange Blossom
White star flower of an Orange Blossom

The orange blossom is a great flower, but you might be waiting a while for this white flowering tree to produce flowers and consequently fruit. 

This flower is significant in many cultures, commonly used for marriage ceremonies as it symbolizes love, fertility, and purity. 

The flower itself is also extremely fragrant, with a sweet and gentle citrus scent. The blossoms are small and white in color, with five petals that are clustered over each other. 

In the center is a white cone with a touch of yellow, similar in shape and design to the jasmine flower. 

Botanical Name:  Citrus sinensis 
Growth Rate:  Moderate 
Native Range:  Southeast Asia 
Hardiness Zones: 9-11
Dangers: Non-toxic 
Soil Needs:  Well-drained soil
Exposure: Full sun
Ease of Care: Moderate 
Diseases: Citrus canker, citrus greening
Propagation: Seeds, grafting, budding 
Fertilizer: Citrus fertilizer 
Pests: Citrus leafminers, aphids, scale insects 
Blooming Period: Spring 
Pruning: Minimal 
Water needs: Regular water needed 
Orange Blossom Growing Guide Chart

10. Orange Zinnia (Zinnia spp.)

Orange Zinnia
Close-up of the Orange Zinnia flower

The orange zinnia is one of the most spectacular orange flowering perennials. It is a favorite with gardeners for its bright color and showy petal structure. It has a large daisy-like structure with a single layer of petals originating from the center. 

The Orange zinnia is mostly found in a bright orange color, but some varieties showcase light peach, pink, and deeper shades of orange. The flower is associated with warmth, joy, energy, enthusiasm, and positivity. 

These are excellent for planting in containers, along garden borders, or as cut flowers. 

Botanical Name:  Zinnia spp
Growth Rate:  Fast 
Native Range:  Mexico and southwestern United States 
Hardiness Zones: 2-11
Dangers: Non-toxic 
Soil Needs:  Well-drained soil 
Exposure: Full sun 
Ease of Care: Easy 
Diseases: Leaf spot, powdery mildew 
Propagation: Seeds or plant starts 
Fertilizer: Moderate fertilizer requirements
Pests: Spider mites, caterpillars, aphids
Blooming Period: Summer to fall 
Pruning: Pinching back stems will promote bushier growth 
Water needs: Regular watering 
Orange Zinnia Growing Guide Chart

11. Orange Cosmos (Cosmos Sulphureus)

Orange Cosmos
Close-up of the Orange Cosmos flower

The color orange is often associated with positivity and warmth, and the orange cosmos flowers are also considered a great way to bring a bit more joy, warmth, and positivity to a garden. 

The orange cosmos are large and daisy-like flowers, with petals surrounding the cone center. The petals are typically a strong orange color, but they can be much darker shades of orange or even light golden. 

The petals on this plant are similar to ferns and this gives them an airy look. These can also be quite tall, reaching 4 to 5 feet in height, so it sits at eye level and certainly grabs a lot of attention. 

Botanical Name:  Cosmos sulphureus 
Growth Rate:  Fast 
Native Range:  Mexico, Central America 
Hardiness Zones: 9-11
Dangers: Non toxic 
Soil Needs:  Well-drained soil 
Exposure: Full sun 
Ease of Care: Easy 
Diseases: Aster yellows, botrytis 
Propagation: seeds
Fertilizer: None 
Pests: Thrips, spider mites 
Blooming Period: Summer to fall 
Pruning: Light pruning will promote denser growth 
Water needs: Moderate 
Orange Cosmos Growing Guide Chart

Final Thoughts 

There you have it – 11 plants starting with the letter O!

You can find plants starting with the letter O that are small enough for a pot on your window sill or as large as a full tree in your garden!  

Choosing the best flower for your needs is about understanding what will work in your environment and what will suit your existing garden setup. 



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