Siberian Iris (Iris sibirica) is a great way to bring early season color to your garden. The plant’s elegant, frilly flowers look particularly effective when planted in a mass in a floral spring border or pot. The narrow, long lasting foliage remains long after the flowers have faded, creating an effective background to showcase other spring flowers.
An elegant plant, the Siberian Iris is surprisingly easy to grow.
Despite their elegant appearance these are pleasingly low maintenance plants.
If planted in the correct position, light, moist and rich soil, these flowers are not only easy to care for but they also tolerate the cold and heat well. As Siberian Iris plants mature they grow into large clumps. These require dividing every few years, but like much of Siberian Iris care this is an easy process.
Here is everything you need to know about growing Siberian Iris.
Different Siberian Iris Varieties
There are a pleasing range of Siberian Iris plants available. These come in a range of colors from pales whites and pinks to deeper purples, blues and vibrant orange hues.
While most cultivars can reach up to 3 ft in height, smaller varieties rarely exceed 12 inches. All cultivars are suitable for beds, borders and containers.
Hardiness varies between cultivars. Most are hardy in USDA Zones 4 to 9. Some cultivars are also hardy in Zone 3.
Take the time to find a plant, or plants, that appeal to your taste and also suit your growing conditions. This makes cultivation a lot easier.
High Standards is a reliable cultivar that produces attractive blue-violet blooms on long, elegant stems. Depending on the conditions the plant can reach 36 to 48 inches in height. Producing similar colored blue-violet blooms, Royal Herald also shares the same preferences and growth habits as High Standards.
The rose and white colored blooms of Strawberry Social help to make it one of the most attractive Siberian Iris varieties. The plant’s blue-green foliage looks its best in full sun positions where the cultivar can reach a height of about 36 inches. Reaching a similar height is the purple or rose flowering Ranman cultivar. Similarly, the reliable Sultan’s Ruby also produces attractive deep magenta flowers.
The compact King of Kings produces delicate white flowers later into the season than other cultivars. Finally, if you want something a little different, the flowers of Butter and Sugar produce attractive yellow and white bicolor blooms.
While bulbs are sold at garden stores the American Iris Society has a list of Siberian Iris nurseries and growers in America. These suppliers often have a wider range of available cultivars which can be mail ordered for fall delivery.
Planting Siberian Iris
Depending on your chosen cultivar Siberian Iris plants can enjoy a spread of up to 2.5 ft, and reach a height of up to 3.5 ft. When deciding where to plant, make sure that you select somewhere with enough space. This means that as the plants grow they won’t overcrowd and smother smaller or slow growing plants.
If you are planting in the soil, your chosen position should be averagely moist. Avoid overly wet positions. This can cause the bulbs to rot.
In warmer areas you can plant in a wetter position such as on the edge of a pond. This helps to keep the plant cool and encourages flowering. Siberian Iris struggles in hot or dry positions.
Plant in a full sun position. While Siberian Iris does grow in partial shade positions it may not flower as profusely.
Plant the corms or tubers in late summer or early fall. In cooler areas you can also plant the tubers in the spring but the plant may not flower as profusely in the first year. Containers can be planted at any time.
Full sun loving plants, finding the right position for your plants encourages lots of healthy growth and flowering.
How to Plant
Siberian Iris does best in rich soil. Before planting, enrich the soil by working in compost, leaf mold or well rotted manure. This is particularly helpful if you are planting in a light or sandy soil.
While the plants prefer an acidic soil they grow just as well in neutral or slightly alkaline soil types. If you are unsure what condition your soil is in, a soil testing kit is an easy way to find out.
Before planting, soak the tuber and roots in warm water for a couple of hours. If your plants were shipped to you with green leaf ferns and soil washed from the roots soak overnight.
Dig a hole 3 to 5 inches deep in the soil. Fan the roots out slightly and ensure that they are all pointing downwards. Position in the hole so that the point where the roots meet the rhizome is no more than 2 inches below soil level.
Working the soil over, and amending with organic matter, helps to create a rich, well draining position.
When you are happy with the position of the plant, gently backfill the hole. Take care not to sink the plant.
Pat the soil down gently, being careful not to overly compact the soil. Water well. A watering can is an easy way to make sure that you evenly soak the soil around the plant.
If you are planting more than one bulb space them 12 to 15 inches apart. Different varieties have different spacing requirements, check the plant information before planting.
Keep the soil moist until the plants are established. This can take up to 8 weeks. If you are unsure how much water to apply, aim to give the plants 1 to 1.5 inches of water a week if it doesn’t rain.
Planting in Containers
Your pots should be clean and have drainage holes in the bottom. For a truly low maintenance garden, plant in self-watering pots.
Fill the pots with well draining, fresh potting soil. A tall plant, Siberian Iris does best in large containers.
Plant as described above, soaking the roots before planting in holes 3 to 5 inches deep. Space the bulbs 8 to 12 inches apart and firm the soil down. Water well and keep the soil moist until the bulbs have established themselves. This can take a couple of weeks.
Position your pots in a full sun position.
How to Care for Siberian Iris
Once planted in a favorable position care is pleasingly straightforward.
In warmer climates foliage forms in the fall. During the winter the plants continue to produce tall growth before flowering in the spring. In cooler areas the foliage won’t emerge until after the last frost has passed.
How Often Should I Water?
After planting aim to keep the soil evenly moist until the bulbs are established.
The bulbs also like regular water in the spring. This encourages larger, healthy flower clumps to form.
A soil moisture gauge is a great way to ensure that your soil isn’t drying out. The Atree Soil Meter not only tells you how moist your soil is, it also allows you to measure the pH levels of your soil and monitor how much light your plant is receiving. This is particularly useful when growing sun loving plants.
Remember pots and planters are often quicker to dry out than flower beds.
During the summer the plants cope better with slightly drier conditions. While you shouldn’t let the soil dry out, be careful not to overwater and drown the bulbs.
When watering, aim to keep the foliage as dry as possible, watering only the soil around the plant. Damp soil can encourage diseases such as mildew to form.
Top Dressing and Mulching
Applying a top dressing of organic matter, such as compost mulch, around the plants helps the soil to retain moisture and cool. As the organic mulch breaks down it enriches the soil. This gives your bulbs a further boost.
Mulching also helps to deter weed growth.
In cooler climates you can also apply a healthy layer of mulch around the plants after the ground freezes. This helps to prevent heaving and thawing. Allowing the soil to freeze and thaw continuously during the winter causes many bulbs and perennials to perish. A layer of mulch prevents this from happening.
When to Fertilize
These are not heavy feeding plants. Apply one dose of nitrogen rich fertilizer in early spring. This encourages foliage to form. Alternatively you can apply a balanced, general purpose fertilizer such as the Miracle-Gro Shake ‘N Feed All Purpose Plant Food. This is a slow release fertilizer that provides growing plants with a steady supply of nutrients.
As flowering ends and the bulb begins to store energy you can apply a second dose of balanced fertilizer.
When planted correctly, these are pleasingly low maintenance plants. With even minimal encouragement your plants will produce scores of attractive blooms.
After Flower Care
Spent blooms can be cut from the plants.
Once flowering has finished allow the foliage to remain in place. The leaves can still provide height and ornamental interest.
While it is still green, the foliage is also gathering sunlight. Converted into energy, this is stored in the blub, and helps the plant to re-flower next year. Water as needed, to prevent the soil from drying out.
As the cooler temperatures arrive the foliage yellows and die backs. This is a sign that the bulbs are becoming dormant. Once the foliage yellows it can be cut away.
In warmer areas the foliage may remain green all year round.
Companion planting is the practice of growing similar or mutually beneficial plants together. Siberian Iris works best when planted alongside other full sun loving spring flowers.
Good combinations include:
Common Pests and Problems
If planted in a favorable position and correctly cared for the Siberian Iris is a largely problem free plant. It is also pleasingly disease resistant.
One pest which does target irises is the iris borer. These pests lay their eggs on garden debris in late summer or fall. The eggs then hatch into larvae that bores and chews through foliage, working its way towards the plant’s tuber.
Regularly check your Siberian Iris plants for signs of infestation.
Borers leave notched wounds and slimy, wet patches on foliage. Once they reach the tuber the pests hollow their way through the root system. They then pupate and hatch as adult moths.
Regularly check your Siberian Iris for signs of infestation. Insecticide sprays are useful for deterring the pest if it is present in your area. Alternatively try washing the foliage in a homemade insecticidal soap. Keeping the area around your plants clean and tidy also helps to deter the pests.
How to Propagate Siberian Iris
Siberian Iris can be propagated either by dividing and transplanting large clumps or by growing from seed.
Dividing and Transplanting
After several years the plants can develop into large clumps. As the clumps grow you may notice the plants forming fewer flowers. They may also develop a less vigorous growth habit. Should these two things occur, your will need to divide the plant.
By dividing the large clump into smaller clumps you help to reinvigorate the plant. This encourages more flowers to form, allowing you to fully enjoy your spring garden.
The best time to divide the plant is soon after flowering has finished for the year. At this point root growth is still active. This means that the transplants, if kept moist, will establish themselves quickly after planting.
With a clean shovel dig up the entire plant clump. Cut the foliage down to a height of about 6 to 8 inches.
Use a sharp knife to cleanly cut the clump into even sections. Each section should have a good root system and several fans of foliage.
Plant each division as described above as quickly as possible. Keep the soil moist for 6
to 8 weeks after planting. This helps the root system to establish itself.
Growing from Seed
If you want to try growing from seed, allow spent flowers to remain on the plant. These give way to seed pods.
In the fall, the pods ripen. Once ripe, carefully watch the pods. As soon as you notice the top of the pod beginning to open, cut the pod from the plant and remove the seeds.
Siberian Iris seeds require a period of cold weather in order to germinate. Gardeners in cooler climates can sow seeds directly into the ground, allowing the natural winter temperatures to chill the seeds. However, growers in warmer climates must artificially create this chilly spell.
To sow the seeds outdoors, sow in the late fall or early winter. Plant each seed to a depth of about half and inch, cover lightly and water in. Germination occurs in the spring, at the same time that mature Siberian Iris plants are in flower. Following germination your seedlings continue to grow throughout the year, before flowering the following spring.
If you don’t enjoy a period of cold weather in the winter, you will need to recreate this artificially. This process is known as stratification.
Soak the seeds in a bowl of water for 5 days. Drain and change the water every day. This removes the germination inhibitor present in seed or seed coat.
Plant the seeds half an inch deep in small pots filled with damp potting soil. Put the pots in a plastic bag and place in the refrigerator. The plastic bag helps to prevent the soil from drying out too quickly.
Regularly check the pots to ensure that the soil isn’t drying out. Gently moisten the soil if it appears dry. A plant mister like the Yebeauty Plant Mister, provides an even, gentle spray that moistens the soil without disturbing the forming root system.
Allow the seeds to remain in the refrigerator for 60 days.
When you remove the seeds from the refrigerator don’t be surprised if some of them have already germinated. The others should germinate within a few days.
Grow the seedlings on in a light position. If you struggle to find a sunny enough windowsill, placing the seedlings under grow lights is just as beneficial.
Gradually harden off before planting outside in the late spring. Water regularly and remember to protect from pests.
During the summer and the fall, as the seedlings grow they develop healthy amounts of foliage. Flowers bloom in the second year.
An elegant flower, these are surprisingly resilient plants that reliably add color and interest to spring gardens.
Coming in a range of colors from deep blues and purples to light pinks and whites, the Siberian Iris is a reliable addition to the spring garden. Their long lasting flowers and distinctive narrow foliage means that these resilient perennials are a standout addition to a mixed flower bed. They are equally attractive when used in mass plantings in flower beds or containers.
Adaptable and hardy, while they are less common than the bearded iris, the Siberian Iris is a worthy addition to any garden.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.