Siberian iris is a beautiful perennial plant known for its striking flowers. It also has a beautiful structure with tall, narrow foliage. These stunning blooms will add texture and color to your garden.
This low-maintenance perennial rarely has problems with pests and diseases, making it a beautiful and practical choice for gardeners.
Plant History and Cultivation
The plant gained popularity in 16th-century Western Europe for its intricate flowers.
Siberian iris is native to parts of Europe and Asia, including, of course, Siberia. It was introduced to Western Europe in the 16th century and quickly gained popularity as a garden staple because of its intricate and beautiful flowers.
In modern times, these plants have been hybridized. Plant breeders have developed many different cultivars that we enjoy in our gardens today.
There are many ways to obtain and grow Siberian irises. Let’s examine all the ways to propagate them and get them growing in your garden.
Buying from a greenhouse or nursery allows you to access diverse varieties.
Purchasing from a greenhouse or nursery is an easy way to get exactly what you want. Many specialty greenhouses will have a lot of interesting varieties to choose from. Yes, this means you are not propagating them yourself, but it does provide the most extensive selection. Remember, you can always propagate your purchases later to expand your garden!
Purchasing rhizomes online offers a cost-effective option with a wider variety.
You can purchase rhizomes from catalogs and websites. Purchasing rhizomes is cheaper than buying a fully-grown plant. It is also a great way to find more weird and wonderful varieties than by visiting nurseries and greenhouses.
Soak your rhizome overnight before planting it. Pick a suitable location and plant the rhizome about 1-2” under the soil. This is deeper than a regular iris. Water it well. It will take around three seasons to establish itself and start to bloom.
Siberian iris benefits from periodic division, ideally in fall or after blooming.
These plants benefit from division. If your iris is growing large but doesn’t have many blooms, it may be time to divide it. You will also notice that it is forming a dense ring of rhizomes. This division is best done in the fall or after they have finished blooming and is best if performed on a cool, cloudy day.
You can dig up the entire plant and use the sharp end to split your plant. I use the rule of thirds: take up to two-thirds of the plant and leave one-third to replant. Replant all the pieces and water them all in well.
Growing from seeds is not recommended due to uncertain flower outcomes.
I don’t recommend starting from seed. They require periods of cold stratification, and there is no guarantee that they will grow true to their parent plant, meaning that the flowers will differ from the plant from which you harvested seeds. Many hybridized plants do not produce true-to-type seeds; instead, the seeds revert to one of the parent plants from that hybrid or may be sterile.
Plant Siberian irises in an ideal spot to support their long-term health and growth.
Since the Siberian iris is a long-lived perennial, it is important to plant it correctly to optimize its health and growth.
Dig a hole about three times as wide and around twice as deep as the plant. Place the plant into the hole. I use two-thirds of the existing soil mixed in with about a third of fresh organic material such as compost or worm castings.
Bury the plant up to the crown, but do not bury the crown itself. You may need to add soil to the bottom of the hole if it is dug too deep. I still recommend digging the hole wider and deeper than the plant itself. This will give the plant a head start to root into soft soil. Water it in well, and provide regular watering for the first season to help it establish.
How to Grow
These fuss-free perennials will grow and flower without much effort if you plant them in their ideal conditions. Let’s examine what those conditions are.
They prefer six hours of sunlight, thriving in full to partial sun.
Siberian irises thrive in full to partial sun. Six hours of sunlight is ideal. They can receive more direct sun if you live in a cooler climate. In hotter climates, I recommend planting them in an area with some afternoon shade to protect them from the heat. Look for areas in your garden with dappled shade, perhaps from a deciduous tree.
Ideal growing conditions include rich, well-drained soil.
These rhizomatic plants thrive in rich, well-drained soil. This is the typical soil in which many favorite garden perennials thrive. But I have seen Siberian irises growing well in less-than-ideal soil conditions. They will be fine if they are not in waterlogged soil. Refrain from planting them in soggy locations.
The plants enjoy moisture but need good drainage to prevent root saturation.
Siberian irises like to be evenly moist but never in oversaturated soil. I find they do like more water than bearded irises. Good soil full of organic matter will help retain moisture without being soggy. The rhizomes will rot if they are left in standing water. You can use mulch to retain water near the root zone.
You can plant Siberian iris near water, such as decorative fountains and ponds. They do like a lot of moisture. Ensure the soil can drain and the roots don’t sit in standing water.
Climate and Temperature Requirements
They are hardy across diverse climates but may need shade and extra watering in hotter regions.
Siberian irises grow in zones 3-9, making them a great option for gardeners nationwide. They are extremely cold hardy and do not need extra protection in cold climates. You might find they need more shade protection from the hot afternoon sun in higher zones. They may also require extra watering when it gets really hot.
Over-fertilization has the potential to impede flower production.
Too much fertilizer can make irises grow a ton of foliage but not as many flowers. Gardens benefit more from amending soil with organic matter than applying fertilizers.
Top dress your garden with organic matter such as compost, aged manure, worm castings, or sea soil. I usually apply organic matter in the fall, but early spring is fine, too.
If you must fertilize, choose an all-purpose slow-release fertilizer and apply it in the spring.
Trim back the flower stalks after blooming.
Siberian iris is a lovely, low-maintenance perennial. I trim off the flowers all the way down the stem after they have finished blooming. This isn’t necessary, but it does eliminate the seed pods from forming.
You might enjoy the appearance of the large seed pods that form after they bloom, and if you do, by all means, leave them in place! I usually cut them back in the fall. But you can leave them and clean up the dead plant material in the spring if you enjoy their look.
It offers stunning flowers and tall foliage, creating a captivating display in late spring.
Irises pack a double punch with their gorgeous flowers and tall, spiky foliage. The intricate flowers bloom in the late spring, which creates a show-stopping display. But even when it isn’t in bloom, the spiky foliage adds an interesting texture to the garden.
They look great as a back and mid-garden plant. I like to add them in groups of three, five, or seven. I stagger them through a garden bed. They look great with plants with different foliage shapes.
Try playing them with the soft, feathery foliage of peonies. The giant flowers on peonies are also a lovely contrast to upright fan-shaped flowers on irises. Both bloom around the same time (depending on the varieties) and will light up your spring garden.
Alternatively, plant them with coneflowers. The Siberian iris will have finished blooming when the coneflowers start to bloom. The spikey iris foliage is a perfect backdrop for the daisy-like coneflowers to take center stage.
Siberian iris also makes an excellent plant for around the edges of ponds and water features. They like moist ground and provide structure and interest at the water’s edge.
There are so many unique varieties to consider adding to your garden. However, beware of websites selling varieties in unnatural colors, such as electric blue and neon purple. If it looks too good to be true, chances are it is!
This elegant variety has ivory-white flowers and vibrant lemon-yellow centers.
‘White Swirl’ is a simple but elegant variety of Siberian iris. It has ivory-white flowers and bright lemon-yellow centers. These will add instant brightness to your spring garden.
The ‘Painted Woman’ Siberian iris boasts striking red and gold downward petals.
‘Painted Woman’ is a showy variety. The downward petals are a blushing red sprinkled with gold accents. The upward petals are ruffled and creamy white. The blooms are large and will attract attention in your spring garden.
‘So Van Gogh’
This variety boasts buttery yellow petals with purple veins and periwinkle upward petals.
‘So Van Gogh’ is one of my favorite varieties. They are a work of art! The three downward petals of the iris are a buttery yellow color with purple veins running through them. Their upward petals are a perfect periwinkle color. They are the perfect color combination for spring.
A unique, ruffly Siberian Iris, ‘Concord Crush’ has layers of violet petals.
‘Concord Crush’ is a ruffly, many-petaled variety. There are layers and layers of soft violet petals with pops of white in the center. This is a unique flower that looks exotic.
Pests and Diseases
When grown in their ideal conditions, these plants have very few problems. But, like everything in the garden, they can be affected by certain pests and diseases.
These borers cause harm to iris plants by burrowing into their rhizomes.
Iris borers are a significant pest for many iris species. The larvae of these moths tunnel into the iris rhizomes. Look for wilting or yellowing foliage and signs of tunneling near the base of the plant.
Infested rhizomes should be removed and destroyed. You can purchase insecticides to use on your irises to prevent them from reinfesting in the following seasons.
Control aphids by blasting with a hose and attracting their predators.
Aphids are small, soft-bodied insects that can feed on foliage and flowers. They may cause leaves to become distorted and discolored. You can often control aphids with a strong blast of water with the hose.
You can create a diverse garden that attracts beneficial insects to devour aphids for you. As a last resort, use an insecticidal soap to control them.
A fungal disease, iris rot causes slimy decay.
Iris rot, also known as bacterial soft rot, is a disease that can affect your Siberian irises. This fungal disease will cause the leaves and rhizomes of the iris to become slimy and decay.
Prevention is the best method of controlling iris rot. Ensure you are planting your irises into their ideal conditions. This means adequate sunlight, well-drained soil, and good air circulation.
Plant your irises 18-24” apart to help with airflow. Watering should be done in the morning so the plant can dry off in the sun. Night watering leaves the plant wet overnight and invites fungal diseases to grow.
Remove and dispose of the damaged leaves and rhizomes if you notice iris rot. Apply a fungicide as necessary. You can also apply them as a preventive measure if iris rot becomes an ongoing issue.
Iris Leaf Spot
Manage iris leaf spots by optimizing plant conditions, spacing, and fungicide use if necessary.
A fungal pathogen causes iris leaf spots. This condition can be identified in your plants as dark spots on the foliage with yellow halos around them.
Again, keeping it in its ideal conditions and ensuring they are spaced to allow good airflow is crucial. If you notice iris leaf spot, remove any damaged leaves. You may also need to apply a fungicide to control it.
Frequently Asked Questions
A: Around every 3-5 years. If your iris doesn’t bloom as fully as it used to, it is a sign it needs to be divided. Make sure to divide your plants on a cool day after blooming. It is a good fall gardening task!
A: While the rhizomes of the iris will grow, it spreads slowly and not in an invasive way. Once the rhizomes have spread, you can divide them for more plants to place around the garden!
A: This depends on how you obtained your plant. From a division or bare root, your iris could take up to three seasons to establish and bloom. A plant bought from a garden center could start blooming the following season.
A: Blooms typically last around two to three weeks, starting in the mid-late spring.
Siberian irises are a fuss-free perennial that can greatly impact your garden. It adds height and a structural element with its spiky foliage. Then, the spring blooms are a spectacular burst of color. There are lots of varieties to fit your unique garden style. I recommend adding one (or more!) to your perennial garden.