Yellow iris – info, planting, care and tips

Yellow iris (Iris pseudacorus)
Yellow iris (Iris pseudacorus)

The yellow iris, also known as water flag, is with its bright yellow flowers and sword-shaped leaves a valuable swamp perennial.

Profile of yellow iris:

Scientific name: Iris pseudacorus

Plant family: iris family (Iridaceae)

Other names: yellow flag, water flag

Sowing time: late autumn, early winter, spring is possible too

Planting time: autumn

Flowering period: May to July

Location: sunny to partially shaded

Soil quality: nutritious, humus rich, sandy to loamy, moist to swamp

These information are for temperate climate!

Use in: individual position, group planting, planters, pond planting, under planting, nature garden, pot garden, water garden

Winter hardiness: hardy

Bee and insect friendly: yes

Plant characteristics and classification of yellow iris

Plant order, origin and occurrence of yellow iris

The yellow iris (Iris pseudacorus) is widespread from Europe to Asia and has established itself as a garden refugee in North America. In nature, it likes to colonize the banks and siltation areas of standing and flowing water. You can also find them in low moors and in swamp forests. It belongs to the iris family (Iridaceae). All parts of the plant are considered poisonous, but especially the rhizomes. In the past, the root with its tannins was used for tanning leather and an extract used from the dried root for various medical purposes.

Characteristics of yellow iris


Yellow iris sprouts sword-shaped, long leaves from its thick, underground rhizome and then later grows its flower stalk. It reaches a height of about one meter (40 in). Thanks to their persistent and creeping rhizome, larger stocks will grow soon.


With its linear, stiffly upright and up to one meter (40 in) long leaves, yellow iris is a center of attraction on the pond bank. Its gray-green leaves are up to 3 centimeters (1.2 in) wide and have a pronounced midrib.


The flowers of the water flag show up between May and early July. They have the typical iris flower shape with upright and hanging leaves in rich yellow. The yellow of the hanging leaves is streaked in the middle by purple veins. The individual flowers do not last very long, but there are always several on a flower stem that bloom in succession. Hoverflies and bumblebees are the main pollinators.


After pollination, the yellow iris forms cylindrical, three-chamber capsule fruits. They grow to be about 5 to 7 centimeters (2 to 2.8 in) long and contain innumerable seeds inside. These are floatable for a long time and can even survive in the water or mud for several years.

Flower of yellow iris
Flower of yellow iris

Yellow iris – cultivation and care


As in nature, the water flag prefers a sunny to partially shaded spot in the garden, which is wet to moist. It thrives particularly well in the swamp zone with a water depth of up to 20 centimeters (5 in). It also tolerates a higher water level, but then it does not bloom so abundantly.


Yellow iris is quite hungry and thirsty, so you should plant it in a well-nutritious, moist soil. Usually not a problem at the edge of the pond, but normal garden soil often has to be prepared:

  • The soil should be humus-rich
  • The soil must be able to hold moisture well
  • Slightly loamy garden soil usually have just the right degree of permeability
  • Even well-maintained natural garden soil pose no problems
  • Sandy soils can be difficult because the water flows down the shallow roots. They should be enriched and compacted with a little clay powder
  • Otherwise, nutrient-poor soils cause more problems than over-fertilized ones
  • Iris pseudacorus likes to draw the excess nitrogen from over-fertilized soils
  • Mix in mature compost in nutrient-poor sandy soils before planting


Seeds of Iris pseudacorus can be ordered online, but it is not for nothing that seeds are often given the note: “Experience in sowing and growing is necessary. Not suitable for beginners ”. If you want to try it, you should do the following:

  • The cold germs should best be sown in late autumn or early winter
  • As dark germs, they must be covered with earth at least a finger-thick
  • The growing pots must remain outdoors or be placed in a cold frame
  • Because they need frost in winter, covering with snow should be an advantage
  • The sowing must never dry out completely
  • The seeds should then germinate in spring (from March to late April)

Sowing in spring is also occasionally successful and is treated as follows: sow, keep warm and moist for 2-3 weeks, then put in the fridge for at least 4 weeks, then wait for the germination outdoors and plant out the young plants. This might not work for all varieties, a treatment with germ-accelerating gibberellic acid can help a little in this regard and possibly even replace the cold treatment in the refrigerator.


One can also purchase the yellow iris as a young plant and plant it out immediately. If you have patience and put the plant to one side with space to spread, you can plant it as a specimen plant. If the beautiful iris is to appeal immediately, it is better planted in a small group.

The best time to plant is autumn, at the edge of the pond and in the bed. The following applies: the beautiful yellow iris has a pretty strong urge to spread, which you can only control when planting:

Iris pseudacorus forms a powerful rhizome as a survival organ. This rhizome creeps almost horizontally through the earth and constantly produces new plants. Much to your delight when the yellow iris is supposed to spread, but inconvenient if it should stay in the same place or other, less competitive plants should also thrive in the shallow water zone. That is why yellow iris is mostly planted in plant tubs and kept under control. You can also put the iris as a group in a large planting tubs. The spread can also be controlled somewhat via the exact location of the planting. If the iris is planted a little further into the wet meadow, not in the swamp area, it will not grow as much. However, it there will usually not even reach a height of one meter (40 in).


The propagation of yellow iris is possible in several ways:

  • The native wildflower initially spreads itself to considerable stands, of course, this only if it is not prevented by a planting basket
  • The plant can be propagated vegetatively by dividing the rhizome. One piece of rhizome is enough to create many new irises
  • For this cut off a part of the rhizome in autumn, plant immediately and in spring the new yellow iris will grow
  • The seeds of yellow iris spread easily through self-seeding in the garden. The ripe seed pods can also be collected for seed production. Sowing and the difficulties involved have already been described above.

Care / Watering / Fertilization

In a pleasant environment, the yellow iris behaves like it does at the natural site: It blooms abundantly, even if it is not constantly divided and transplanted.

It only needs enough moisture and from the start of budding (usually in March) until the end of the growing season at the end of July / beginning of August, some good organic fertilizer (ripe compost, guano, plant swill). Do not fertilize on dry root balls as there is a risk of burns, do not fertilize after shoot completion around mid-August. During the resting period plants do not absorb any nutrients, they cannot mature properly and are more sensitive to frost with soft shoots. Otherwise, the following applies when fertilizing: “Less is more”. The bottom of the nitrogen-loving iris only needs to be improved a little if the cluster has less and less flowers. Then fertilization is done in spring from the start of the shoot until the yellow splendor is fully back on.


You don’t actually have to cut the yellow iris, the wildflower usually also flowers reliably if the flowered shoots simply remain on the plant. If the garden pond including the edge of the pond is to look neat, you can also cut away all the faded flowers, bloomed shoots, withered leaves immediately, an unspoilt plant like the water flag can easily take this. You have the choice of removing the individual flower stalks by cutting as far down at the base as possible or cutting back the whole cluster with leaves in the first warmth of spring, as it is often recommended for “regular shrub pruning”.

Diseases and pests

In bad weather, rust sometimes appears on the leaves of the water flag. The females of the iris weevil, a species of beetle, lay their eggs almost exclusively in the young fruits. When the fruit ripens in late summer, the young beetles drill a hole in the pericarp and so leave it.


Yellow iris is hardy, so no winter measures must be taken.

Use in the garden

With its tall growth and bright yellow flowers, the water flag sets striking eyecatcher in the swamp zone at the garden pond or stream. They can also be used in shady garden areas with constantly moist soil. The stately plant is also well suited for use in large planters.

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