Iris Bulbs (Bulbous Iris) – A Quick Guide

We love having flowering plants in our garden for their colorful foliage. Iris bulbs are among the favorite perennial plants that most people would like to have in their garden. 

There are a lot of different Irises. Each has different characteristics. With up to 300 species, they are divided into many groups or sections depending on how they grow and how their flowers look.  However, they are classed as rhizomatous irises (irises that grow from rhizomes) and bulbous irises (irises that grow from bulbs).

In this article, we will be talking about bulbous irises or what we commonly called iris bulbs.

What are Iris Bulbs?

Irises are perennial plants that have long, erect flowering stems that are either simple or branched. Their stem can also be solid or hollow, some are flattened and others have a circular section. Their flowers being at the end of the stems are looking so proud of their beautiful colors, shapes, and scent.

Iris bulbs or bulbous irises grow from bulbs. The bulbs are usually round or pear-shaped with the size like the tip of your thumb or a bit smaller. They are about 2-5 inches when they are under the ground. While the rhizomatous irises have 3-10 basal sword-shaped leaves growing in dense clumps, the bulbous irises have cylindrical basal leaves.

Iris bulbs that bloom in winter and spring are usually smaller. While hybrids appear in early and mid-summer are taller and flowers are larger.  Most of these are hardy and prefer light well-drained soil.

After their flowering season, bulbous irises shed their leaves and they undergo a dormant phase, usually by summer. However, when the leaves start wilting, the bulbs are considered ‘pregnant’. It is advised not to remove those leaves as they provide the extra nourishment the plant needed. This is the time when the development of the buds for the ensuing season takes place. Therefore, they also need to be taken care of especially during the last couple of months of their growth. 

Types of Iris Bulbs

There are 2 types or groups of Iris bulbs. These are Xiphium and Scorpiris

1. Xiphium

Also known as the small bulbous-rooted iris and commonly called Spanish Iris, which is, of course, a native to Spain and Portugal. The colors of the flowers are usually white, blue, violet, and yellow. They are around 6 cm wide, and the greyish-green leaves grow between 20-70 cm. The plant can reach a height of up to 80 cm.

These bulbs are rootless during the resting stage. Bulbs are smooth except those of the reticulata irises, which are characterized by a netted or reticulated covering.

They typically flower in May and June, but the leaves usually emerge during autumn. The leaves die after the flowers fade.

The Spanish iris is popular among the florist for their striking color combinations such as the Lusitania. Other examples of these xiphium irises are “Blue Angel’ (mid blue), ‘Purple Sensation’ (purple), ‘White Excelsior’ (white, with a yellow stripe down the fall centers), and ‘Golden Harvest’ (deep rich yellow)

The hybrid variety of this type is called Dutch Iris, also called Iris Hollandica. The multi-colored, 6 petal flowers are about 3-4 inches, and they bloom from May to June. The plant size is about 15-24 inches tall.

2. Scorpiris

Commonly called Juno. It has thick, fleshy roots that continue during the resting stage. With about 60 different species, makes it the largest group of bulbous irises. They are mostly native to the Middle East and Central Asia (except China).

Scorpiris are dormant in summer and then the leaves grow in mid-winter or early spring. Most of these iris make fragrant flowers. They are mostly not frost-hardy, too, which makes these plants best grown in greenhouses. Their height can reach from 24-35 cm (10-14 cm).

A few examples of these are Iris maracandica, planifolia, and rosenbachiana, which are all scented. Irises lusitanica, tubergeniana, and bucharica are some of these unscented varieties. 

While Irises Sindpers, and Blue Warlsind are two of the hybrid varieties.

Planting and Growing Iris Bulbs

Learning how to plant Iris Bulbs is not that difficult. Iris bulbs are easy to grow and are low maintenance. Most of them like to be in full sun. But some of them can be grown in a part shade like the Dutch Iris, Iris Versicolor, some Siberian Iris, and Louisiana Types of Irises.

Iris bulbs have particular characteristics. After their flowering season, they shed their leaves. They also go dormant during the summer. And they can be grown from their seeds. However, when propagated from their seeds, their first flower appears much later compared to those that are grown from bulbs.

When buying iris bulbs, instructions are usually included on their packs about when is the right time to plant them.

However, most of the irises are best planted during fall, and will mostly bloom during spring.

Here are a few more things that you need to know on how to plant the iris bulbs.

How deep do iris bulbs should be planted

It is important to know how deep do iris bulbs need to be planted. If the bulb is planted too deep, it may rot. Especially if the soil is heavy and doesn’t drain well. Create a hole about 6 inches deep, and wide enough for the roots to spread.  To improve drainage, combine the hole with peat moss or compost.

Plant the bulbs with the pointed tip up, about 5 inches deep. Irises look great when they are planted. Then cover with well-draining or loose soil.

Most irises, especially the Dutch irises, like to be planted in large groups. You can plant about a dozen bulbs per square foot, or about 4 inches apart.

They can also be planted in containers or raised beds but make sure they are draining well. 

The best soil for the Iris Bulbs

As mentioned, the soil should be draining well. If the soil has something like clay-like consistency, add some organic matter, humus, and some sand into the soil. A raised bed can be a good idea if not planting in containers.

Upon planting, a well-balanced fertilizer can be mixed with the soil as a good start for the irises. Then a general liquid fertilizer once a month for 3 months, and then nothing more especially if you can see that they are growing well. However, give them a top dressing every year during early spring.

As with any other flowering plant, watering is important. Thoroughly water them as you planted them. When they are established, their roots can store water. Just water them enough. Although they like it moist, do not allow the soil to be soggy. That’s why well-draining soil is important. The bulbs usually root fast after that.

Because they are planted during the fall season, the bulbs, in the meantime, will go dormant when the temperature drops. In areas where there is freezing, it is advised to mulch them with straws or hays to ensure the bulbs are safe. This is especially in the first year after planting.

As the spring approaches, the soil will start to warm up. At the same time, the irises will start to grow and then bloom. After flowering, their leaves die out and the bulbs will be dormant until the next spring. After everything takes place, these iris bulbs should be blooming every season.


When the foliage of the irises died down, dig and lift out the bulbs. Divide the bulbs and store them until it’s planting time again in the autumn.

However, Iris bulbs can stay in the ground for several years. To take care of them when the foliage die down during the cold season is to mulch them to protect the bulbs. They would spring back and bloom again the next spring.

Over the years, overcrowding of bulb clumps in the ground affects their blooming capacity. It is advised to divide them every 3 to 5 years after they start blooming. And it is best to divide them 1 month after flowering. This is also the best time to check if the bulbs have any problems and infestations and are able to treat them accordingly.

Dividing the bulbs is easier than dividing rhizomes. All you need for the clumps of bulbs are to separate them. Rhizomes need to be cut and have to dry up the cut part for several days.

To divide the clumps of bulbs:

Using a shovel, dig up the ground around the plant carefully not hitting the clumps. Pull them up. Carefully separate each bulbs, and at the same time check for any problems. Remove those that look  week or dead. Carefully remove extra dirt to clean them up and store in cool dry place. If any of the bulbs have started to sprout, replant them.

Propagating the Iris Bulbs from Seeds

Any gardener would love to learn how to propagate the iris bulbs to continue growing them and to grow more. Although they can be grown from seeds, they tend to bloom much later than growing them from bulbs. 

However, seeds are a lot cheaper than bulbs. If you have the patience and prefer to wait a little longer, at the same time, you’d like to save a bit so you can buy more varieties of irises or other plants, propagating Iris Bulbs from seeds is perfect for you.

Irises produce seed pods after they bloom. To be able to allow them to produce seed pods, don’t cut off the flowers or avoid deadheading them when the flowers wilt. You will see a green oval-shaped on top of the stem after the flower fades. Let them ripen until they become brown and start to split open. Then cut them off and store them in a cool dry place until it’s time for them to start germinating.

Just like when planting the bulbs, the best time to sow the seedlings are during the fall season. You can have them in the container or straight to the soil.

But the trick here is to soak these seeds in water for at least 28 hours, and up to 2 weeks. The water should be changed daily. Use a strainer to catch the seeds when changing the water.

You will notice that the seeds will become plump. This will make the seeds germinate easily. Then plant them in a container with germinating soil mix, or straight to the ground in your garden (a prepared area with amended soil). Plant the seeds half an inch deep and about an inch apart.

Here is something else to learn about seeds:

Keep the soil moist but not soggy. Never let them dry out. There will be poor germination if the soil is always dry. When there are seeds that do not germinate, let them sit for a while and wait until spring. You’ll see most of them sprouting.  Iris seeds have the ability to germinate even after more than 2 years.

Some gardeners who prefer to germinate the seeds in a container will put them in plastic bags to retain the moisture and then refrigerate them for up to 60 days. When you do this method, plan ahead on when to start germinating your seeds. 

The seedlings look like grass when they sprouted. That’s why it is important to make sure that the ground is weed-free. As they develop, the arrangement of leaves looks like a flat fan. Start transferring them into their permanent location when they are a few inches tall. Leave those that did not sprout. They will germinate next year.  

Their first bloom (maiden bloom) depends on the climate. If the climate is warm, these irises will have their maiden blooms on the first spring when they sprout. If the climate is colder, they will not flower during the first spring. They will have their first bloom in the second spring or after that.

Don’t be surprised if their flowers are not the same color as their mother plants especially from those that are hybrids. It’s a natural thing. But at least you’ll have a unique iris.

Another flowering Plant that grows from bulbs

There you go. Planting iris bulbs is not that hard and is very rewarding. There are so many of these varieties to choose from. You can select the types that are also suitable to your area.

If you have that patience and would love surprises, growing from seeds is just perfect. Do you know that seeds still germinate even after several years? Some types can reach 18 years of germination period.

Here are something that are perfect for your garden, too.

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