How to Grow Yellow Iris

Closeup of yellow iris flower.

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Yellow iris or "flag" grows wild in wetland areas throughout North America, except for the Rocky Mountain states. It is not a native but naturalizes easily. In fact, the yellow iris is considered invasive in parts of North America because its rapid spread allows it to out-compete native species.

Many American gardeners give up on the thought of growing yellow iris in the landscape once they learn that it is invasive, and this is too bad.

Not only does it bear attractive flowers, but it also has striking, sword-shaped leaves (1 1/8 inches wide) that are a nice greenish-gray color. The large seed pods that succeed the blossoms are well-suited to being used in dry flower arrangements too.

Its benefits extend beyond the fact that it adds wonderful color to the yard. It is also easy to grow, low-maintenance and useful as an ornamental pond plant. It is valued for its ability to live in wet areas of the landscape where many other plants would perform poorly, plus it is deer-resistant.

Luckily, there are ways to counteract its invasive tendencies, thereby allowing you to safely include it in your landscape plan.

Or, alternatively, blue flag iris (Iris versicolor) is a great alternative for American gardeners seeking a native iris to grow in a water garden. It likes the same conditions as the yellow iris, grows to be around three feet in height, is violet-blue, and is indigenous to North America.

 Botanical Name  Iris pseudacorus
 Common Name  Yellow iris, yellow flag, yellow flag iris, water flag
 Plant Type  Herbaceous perennial
 Mature Size  3 feet tall
 Sun Exposure  Full to partial sun
 Soil Type  Medium to wet, with average fertility
 Soil pH  Acidic
 Bloom Time  May to June
 Flower Color  Yellow, with bluish-brown veins
 Hardiness Zones   5 to 9, USA
 Native Area  Europe, northwest Africa, and western Asia

Yellow Iris Care

Yellow iris spreads via fast-growing underground rhizomes and by self-seeding. It uses this flexibility to form large colonies under the right conditions. This is why it is such an invasive plant. If left unchecked, much of your work in caring for yellow iris will consist of pulling it out of areas where it does not belong.

Happily, there are tricks that you can adopt to prevent this from happening. For example, grow it in a container.

If you are not growing yellow iris in a water garden, there is a different tactic that you can use to check its spread. This plant prefers constant moisture. If it is deprived of that moisture, it grows less vigorously. Take advantage of this fact to enable yourself to grow the plant without having to worry so much about its spreading (although you should never let its soil dry out completely).

Finally, whether you grow it as a water garden plant or not, remove the seed pods as soon as they form to prevent self-seeding.

Light

The wetter the soil that yellow iris is growing in, the more sun it can take. Most garden soils are not as wet as those where yellow iris is typically found growing in the wild. For this reason, it is usually better to grow yellow iris in partial sun in a garden setting. But if you are growing it in a water garden, give it full sun.

Soil

Yellow iris grows in wetlands in the wild, so it will perform best if you can provide it with a boggy soil in your landscape.

Water

While it likes a wet soil, yellow flag will survive in a soil that is only moderately moist. But you will have fewer flowers if you grow it under the latter conditions.

Fertilizer

Yellow iris needs no more than an average degree of fertility in its soil. Fertilize it occasionally with manure tea.

Growing Yellow Iris in Containers

To prevent unwanted spread via rhizomes, many gardeners grow this plant in containers. If you are using yellow iris in a water garden, sink the container right down into the water (a stone mulch will help keep the soil in the container). Yellow iris can be grown in water as deep as six inches.