Southern Blue Flag: How to Plant and Grow Iris Virginica

Thinking of planting an Iris virginica in your garden? This carefree aquatic plant, usually found in the wild across the Southern and Eastern United States, is the perfect addition to any water-heavy spots in your garden. Gardening expert Madison Moulton examines the best ways to plant, grow, and care for the Southern Blue Flag.

Nestled the balmy heat of the Southeastern United States, from Virginia to Louisiana and into Texas, sits Iris Virginica – a delicate herbaceous perennial. The small, intricate blue blooms top long stems, surrounded by spiked green leaves that contrast in texture and structure.

Looks are not the only thing this showy plant has going for it. It is also incredibly low maintenance, growing well anywhere it is provided wet soil. This makes this Iris which has a striking blue flower, an ideal addition next to ponds or streams, or as a part of a water feature.

Although it resides largely on the South coast, this plant will thrive in a range of climate regions. No matter where you reside, you won’t regret adding this plant to your water garden.

Southern Blue Flag Overview

Purplish Flower in Green Grass
The southern blue flag is also known as the iris virginica.
Plant Type
Herbaceous Perennial
Plant Family
IRIDACEAE
Plant Genus
Iris
Plant Species
Iris virginica
Hardiness Zone
USDA 5-9
Planting Season
Spring to Summer
Plant Maintenance
Low
Plant Height
Up to 3 feet
Flower Color
Blue
Plant With
Aquatic Plants
Don’t Plant With
Plants Prone to Root Rot
Soil Type
Rich, Loamy
Plant Spacing
2-3 feet
Watering Needs
High
Sun Exposure
Full Sun
Attracts
Bees, Hummingbirds
Pests
Iris Borer
Diseases
Disease-resistant

What Is Iris Virginica?

The Virginia Iris is a member of the Iris genus, containing hundreds of species with similar detailed, interesting flowers. The genus name comes from the Greek for ‘rainbow’, seemingly referring to the colorful flowers found across these fascinating species.

Iris Virginica is Native to the Eastern and Southern coastal regions of the United States, it features bluish-purple blooms surrounding a yellow and white center. The yellow patch is believed to guide pollinators to the nectar inside the center of the flower. Each petal is decorated with deep violet veins that stand out against the light base. The delicate flowers are surrounded by clumps of sharp green leaves that add volume to the plant.

This plant is commonly compared to its Northern counterpart, Iris versicolor. Both Iris species are incredibly similar, growing in the same wetland conditions and sporting similar flowers. However, Northern Blue Flag is understandably more cold-hardy, growing well in USDA zones 3-9.

Southern Blue Flag (and Northern Blue Flag, too) is mostly found in the wild and not typically grown in home gardens. They are skipped over in favor of their more popular ornamental relatives. However, this shouldn’t stop you from growing it in your own backyard.

These plants provide the classic Iris look we all love in wetland conditions. This makes them ideal for tricky spots like ponds, or planted in rain gardens, where they will grow without fuss. They are also native to the US, a great alternative to some of the invasive Iris species that disrupt the local environments.

Propagation

Blue Colored Flower Outdoors
There are a few ways to correctly propagate the iris virginica.

In the wild, Virginia Iris spreads by dropping seeds or slowly extending the rhizomes. When left to spread on their own, the clumps can become congested, preventing further prolific growth and flowering. When kept in your garden, it is best to divide and replant the rhizomes every few years to promote flowering. Alternatively, you can harvest the seeds and replant them immediately, straight into the garden.

Dividing Southern Blue Flags

Division is best done in late summer or early autumn. When the leaves begin to yellow, you’ll know the plants are ready to be propagated. Divide after the plant has finished flowering to enjoy the best of its blooms for that season and limit the risk of bacterial soft rot.

To divide, gently lift the plant out of the soil with a fork, ensuring you do not damage the rhizomes. Depending on the age of your plant, you may be able to pull the rhizomes apart, but if not, they can be cut with a clean, sharp knife. Use this time to remove any unhealthy rhizomes or dying leaves. New, healthy rhizomes will be plump with plenty of leaves, while older ones will have a woody texture.

Cut the leaves to around a third of their height. This allows the plant to focus its energy on rhizome regrowth, limiting any potential transplant stress. Replant the viable rhizomes back into the garden, ensuring they have plenty of sunshine and water to reestablish themselves.

Propagating From Seeds

When propagating from seed, plant immediately after harvesting when the seeds are still ripe. You’ll know the seeds are ready when the pod turns brown and dries out. Iris virginica seeds do not respond well to being stored and, if allowed to dry out, will no longer be viable. Plant the seeds straight into the garden in fall and they should emerge again come springtime.

Planting

Planted Iris Virginica
This particular plant should ideally be planted in early spring.

Rhizomes are best planted in fall, but potted plants can be transplanted into the garden in early spring to get the most of their late spring and summer flowers. Plant around 2’ apart to give the plants enough space to spread.

Ensure the area you are planting in has plenty of sunlight and receives a good amount of water throughout the day. Ideal spots include bog gardens or rain gardens, or along streams and rivers.

This perennial can be planted as a border plant in garden beds, but will need constant watering to thrive. When planting in beds, ensure you pair it with other water-loving plants to match their needs. As they need consistently moist soil, most other common bedding plants will succumb to root rot under the same conditions.

Care

One of the great benefits of growing this plant species is its remarkably carefree nature. When given the right environment, this plant will grow and flower reliably for many years without too much intervention from you.

Light

When it comes to light, this plant needs plenty of sun to produce its showy flowers. In most regions, it is best planted in a full sun position. However, in hotter areas, it may benefit from some shade in the afternoons. The more shade this plant receives, the less likely it will be to flower.

Water

Blue Flag Near Water
Blue Flags should be planted around plenty of water.

Water is the most important factor to consider when planting. Native to coastal wetland areas, this plant is used to consistent water supplies in its natural environment. These conditions need to be replicated in your own garden in order for your Virginia Iris to thrive.

The general rule of thumb for most garden plants is moist, but not waterlogged soil. That is not the case for this Iris species. It appreciates wet, soggy soil, and can even grow well in shallow waters up to 6 inches high. This makes it a great option for planting in water features, or any areas around your garden with inadequate drainage.

When planted in regular beds, it will need constant watering, especially on hotter days. In the interest of saving water, it is therefore best reserved for spots that receive a lot of water naturally.

Soil

Along with plenty of water, the streams and rivers where this plant can be found provide an abundance of nutrients. In these areas, soil is constantly being replaced, with new nutrients essential to plant survival transported with it.

This means your plant will appreciate rich, nutrient-dense soil enriched with tons of organic materials. Loam or clay soils are best (as long as they hold plenty of water). It prefers to grow in slightly acidic soil, with a pH just above 6, but will be just as happy in soils with a neutral pH. Add plenty of compost to the planting site regularly for best results.

Temperature & Humidity

Blooming Blueish Flower
This particular plant does best in USDA Zones 5-9, with moist and moderate climates.

Virginia Iris grows well in the range of temperatures under USDA Zones 5-9, but tends to prefer more moderate climates. In lower temperatures, it may need some protection from harsh weather using a frost cover. In higher temperatures, it will need some extra watering and potentially a shadier spot, depending on how much direct sunlight the plant receives.

Higher humidity areas are ideal for this moisture-loving plant. However, with enough water, it will grow happily in areas with drier air too.

Maintenance

This plant requires very little maintenance. When planted in the right spot, this plant will grow and spread successfully without intervention.

Once the plant has finished blooming, you can cut down the stems to keep the plant tidy and promote further flowering. However, if you’re looking to harvest seeds, keep the stems up until the large green pods have developed and dried out.

Mulch regularly with compost to retain moisture in the soil and provide additional nutrients throughout the season.

Pests & Diseases

Butterfly on Purple Flower
This plant is very resistant to both pests and disease.

Grown in its native habitat, the Virginia Iris is remarkably resistant to a range of pests and diseases. It is also deer resistant, giving gardeners few pesky problems to deal with.

The only pest you may be unlucky enough to encounter is Iris borer. This caterpillar feeds on the many iris species, chewing the leaves and tunneling straight down to the rhizome. Unfortunately, once this caterpillar has damaged the rhizome, it is often too late to repair.

Prevention is the best defense in this case. Inspect the leaves regularly for signs of iris borer and pull any plants you suspect of harboring this pest before they have the chance to reproduce.

Plant Uses

Blue Flower in Garden
Blue Flags are primarily ornamental flowers.

Southern Blue Flags have many wonderful uses in home gardens.

Its main benefit is its water-loving nature, making it ideal for spots in your garden where many beloved plants won’t grow. Areas without drainage that receive plenty of rain or natural runoff are also perfect, as the plants will soak up the excess water and tolerate growing in shallow water in cases of flooding.

When planted in pots, they can be placed in shallow water features near other aquatic plants. Their height, reaching up to three feet, is also ideal for stream borders.

The flowers not only look good to us, but they are also appreciated by a range of pollinators. The blooms will draw in bees, butterflies, and even birds. If you want to keep their beauty all to yourself, the stems can be removed and brought indoors for a stunning cut flower bouquet.

It has also been used as a medicinal plant throughout American history, pounded into a paste and applied on the skin to treat wounds.

Frequently Asked Questions

When Do Southern Blue Flags Bloom?

This plant blooms from late spring through to summer, when the weather is warm.

Southern Blue Flag vs. Northern Blue Flag: What’s The Difference?

The main difference between these two plants is their origin, predictably split between north and south. However, there is some overlap in the areas these plants grow best in, with Southern Blue Flag found in some Northern parts of the Eastern United States. They both grow in the same wetland conditions, but Iris versicolor is more tolerant of the cold than Iris virginica, growing in zones as low as 3.

Final Thoughts

You may spot this stunning plant growing in the wild while strolling along a river, proudly displaying its violet blooms on 3’ long stems. This beauty shouldn’t be resigned to the wild, and it doesn’t have to be when grown in your backyard.

Southern Blue Flags are best grown as an aquatic plant, ideal for Iris lovers with water sources in their garden. This plant is not fussy, is resistant to pests and diseases, and blooms continuously year after year, providing your backyard with beloved Iris charm.

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