Iris pseudacorus a.k.a. the Yellow flag iris is a wonderful companion to have in your plant collection and it will enchant your senses and steal your heart in the blink of an eye. This plant is absolutely gorgeous and can also be super easy-going to have around as long as you pay extra attention to its spread habit.
It is important to mention right off the bat that the Yellow flag iris spreads pretty fast through its underground rhizomes and also by self-seeding. Because of this, the plant can easily become invasive, especially in ideal environments, and occupy too much space in your garden.
This behaviour will affect the plants that grow near your Yellow flag iris. If you want to grow this plant in the garden directly into the soil, you might want to check if it is invasive in your area before adding it to your plant family. In case it is, you can control its spread by planting it in a container and you will have no issues or stress along the way.
If the yellow iris is not considered invasive in your region, you can consider growing it in your garden. Keep reading to find out more about Iris pseudacorus a.k.a. the Yellow flag iris!
About Yellow Flag Iris
- The Yellow flag iris belongs to the very popular Iris genus which contains between 260 and 300 species of flowering plants. The genus takes its name from Iris – the Greek goddess of the rainbow.
- Member of the Iridaceae family, the yellow iris originates from Europe, northwest Africa, and western Asia. It occurs naturally and thrives in damp marshy areas, swampy woods, wet ground, or shallow water.
- Thanks to its beautiful blooms, the Yellow flag iris was heavily imported to North America as an ornamental plant starting in the late-1700s. The Yellow iris has since been deliberately propagated by gardeners all over the continent and even used by horticulturalists for erosion control and in sewage treatment ponds. This led to the extensive spread of the plant which is now present in all over the United States, with the exception of four states – North Dakota, Colorado, Arizona, and Hawaii.
- The common names for Iris pseudacorus include Yellow flag iris, Yellow flag, Yellow iris, and Water flag. The specific epithet “pseudacorus” refers to the leaves of its plant, “false acorus”, which are similar to those of Acorus calamus.
- In a UK plants survey, the Yellow flag iris gained second place for the impressive quantity of nectar these plants produce daily. It comes as no surprise that the yellow iris attracts various species of beneficial pollinators, including native bees and butterflies.
- The ‘Roy Davidson’ and ‘Variegata’ cultivars are recipients of the prestigious Award of Garden Merit. Other lovely cultivars are ‘Alba’ and ‘Golden Fleece’.
- The roots and leaves of the Yellow flag iris are poisonous. Because of this, you should grow this plant in a spot where your kids or pets cannot reach it.
- The Yellow flag iris is a great addition to cottage gardens, coastal gardens, city gardens, water gardens, bog gardens, rain gardens, beds, and borders. It is also perfect near streams and ponds and it can also be grown in containers which makes it easier to avoid spreading.
- The most suitable and exquisite companion plants for the Yellow flag iris include Columbine, Alliums, Peonies, Yarrow, Foxgloves, Euphorbia griffithii ‘Fireglow’, Hosta, Persicaria bistorta ‘Superba’, and Polygonatum. You can create beautiful garden arrangements using yellow irises, especially if you plant the irises in the back and smaller, colourful plants in the front. If you want to grow yellow irises near ponds and in bog gardens, you can pair them with other pond plants such as bearded irises, Canna lilies, water hibiscus, etc.
Yellow Flag Iris Features: An Overview
- The Yellow flag iris is a herbaceous and perennial flowering plant. In general, this plant can reach from 3 to 5 feet (0.9-1.5 m) in height. Sometimes, it can grow as tall as 6 feet 7 inches (2 m) but this will happen only in its native habitat.
- Its foliage consists of erect, sword-shaped, and grey-green leaves that emerge directly from the base of the plant. The leaves can measure up to 35 inches (90 cm) in length and about 1.2 inches (3 cm) in width.
- The Yellow flag iris typically blooms profusely from late spring through early summer (May to June). During this tiny period, the plant exhibits eye-appealing, bright yellow flowers adorned with a veining dash of brown or violet on each petal.
- The blossoms show up at the end of sturdy, upright, and branched stalks. They are relatively big, having approximately 4 inches (10 cm) in diameter. Each flower stalk can produce about 4 to 12 flowers.
- Once its blooming period comes to an end, the Yellow iris flag may bear fruits. They are dry capsules of 1.6 to 2.8 inches (4-7 cm) long that contain many pale brown seeds. The seeds are great to use for propagation.
Growing Yellow Flag Iris
The Yellow flag iris is not like the usual species of ornamental plants. This flower will grow healthy and happy in an environment that can provide plenty of moisture. It is the best option if you dream about having a water garden, a pond garden, or if your garden gets a lot of moisture on a regular basis.
If you want to provide this flower with an ideal environment, you can grow your Yellow flag iris in a pot and sink it right down into the pond. You can sink the container as deep as 6 inches (15 cm) without worrying about the well-being of your plant. A nice trick to keep the soil in place when you grow this plant underwater – stone mulch.
In terms of lighting conditions, there is a golden rule to remember if you want to be the owner of a colony of thriving Yellow flag irises. The more moisture these plants get, the more sunlight they can withstand and will actually enjoy as much of both.
In their native habitat, the Yellow flag irises grow in a super wet environment overall including soil. In general, it is pretty difficult to mimick this type of environment or to bring that particular type of soil at home, so it would be better to grow your Yellow flag iris in a setting where it can receive partial sun. However, in water gardens, you can spoil this plant with as much bright and direct light as it can get.
Temperature-wise, we have great news for you! Although the Yellow flag iris looks very delicate, it is cold-hardy in the USDA zones 5 to 9.
This versatile plant can tolerate a wide range of temperatures and will not show any dissatisfaction if it experiences values down to -4 °F (-20 °C). But for optimal growth and even seed germination, the ideal temperatures range from 59 to 68 °F (15-20 °C).
Since the Yellow flag iris grows at its best in wet environments, it becomes more prone to fungal infections. Leaf blotches are a common indicator that your plant deals with a fungal infection.
If you notice them on your Yellow flag iris, we recommend you cut the infected parts off with a sterilized knife. This will prevent the infection from spreading to the entire plant.
Planting Yellow Flag Iris
Before planting a Yellow flag iris, it’s best to think about the natural habitats in which this plant thrives. As mentioned above, the yellow iris will do best in boggy, medium to wet substrates that come along with an acidic soil pH. For nice results, opt for a growing medium that is also rich in humus.
If you want to improve the growth control of your Yellow flag iris, besides growing it in a container, you can also deprive it of moisture a little. This will prevent it from spreading as vigorously as usual and it will leave you with more time for yourself in the future.
When it comes to fertilizers, things are not very complicated! The Yellow flag iris will be happy and healthy is you provide it with the average fertility level of its growing medium. This adds points to prove that this buddy has a low-demanding nature. But if you want to spoil it once in a while, you can feed it with manure tea.
Watering Yellow Flag Iris
If you are an experienced gardener, you will quickly notice that the Yellow flag iris is different from other well-known species of garden plants that usually require well-draining soils.
This plant will appreciate as much water as you can give it without suffering from soggy conditions. In fact, the flowering will be more abundant when the Yellow flag iris grows in moist soil.
In case you are a beginner gardener, this feature will bring you lots of joy while growing and caring for your Yellow flag iris. Since over-watering is the most common mistake among gardeners, this plant will allow you to make mistakes over and over and it will not hesitate to forgive you.
With this plant, it is always better to provide it with water regularly than allow its soil to dry out. An under-watered Yellow flag iris will also perform underwhelmingly, so make sure you water yours whenever it is necessary to maintain the soil constantly damp.
Propagating Yellow Flag Iris
Although the Yellow flag iris is an invasive species and propagation is not very common, this does not mean that you cannot do it if you want to. You can easily propagate yours through division in midsummer to early autumn.
When you feel like it, you can remove the plant out of its growing medium, divide its rhizomes into three sections or so, and then replant each immediately in its permanent flowering spot. The new plants will benefit from a nice, generous touch of water right after you plant them, as this will help them establish themselves in their new environments.
You can also propagate your Yellow flag iris using those seeds you have collected to prevent the plant from spreading as it wants.
After you collect the seeds, you can store them until spring and start them outdoors once the last sign of frost has long passed. Sow the seeds just above the soil to promote faster germination in the presence of sunlight. Likewise, you should water the sowing spots whenever the soil seems dry.
How to Prevent the Yellow Flag Iris from Spreading
Whether you grow your Yellow flag iris in a water garden or not, it would be wise to control its spread via seeds. The Yellow flag spreads quickly via rhizomes and seeds and it can form dense colonies that can replace and crowd other valuable, but less feisty aquatic plants like cattails and other, native plants, including native irises.
The root system of the Yellow flag iris can form a dense mat which compacts soil and prevents seed germination of other plants. Yellow iris populations that grow excessively and overtake entire areas may also reduce the habitat available to native fish and waterfowl.
Large colonies of Yellow flag irises can even cause other types of damage such as clogged irrigation systems and streams and narrowed waterways.
As mentioned above, this plant tends to spread on its own through seeds and will eventually take up more space than you can handle. If this happens, it will increase the difficulty of the caring routine for your plant, as you will have to pull the specimens out of those spots where they do not belong.
Luckily, you can avoid this by removing the seed pods once you notice their presence. Keep in mind that is better to get the seed pods as soon as they form than to wait for them to develop and ripe.
Without a doubt and despite all its bad reputation as an invasive plant, the Yellow flag iris can make a nice addition to bog gardens, cottage gardens, and other types of gardens as long as they are not in regions where this plant is considered a problem.
If you are growing Yellow flag irises, do not hesitate to share your experience in the comment section!