When To Plant Iris Bulbs – Planting Guide 2024

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Irises are reliable and rugged plants that produce beautiful flowers in a rainbow of colors.

And with many species available, you’ll find a wide range of choices as to which variety to add to your garden.

Those new to gardening will find these perennial plants easy to grow. Like any plant, the key is knowing when to plant iris bulbs.

When to plant iris bulbs? To get the best results, you’d want to plant iris bulbs between late summer and early fall. Doing this will result in spring blooms. Make sure it gets at least half a day of full sun or a full day of sun for more vibrant-colored flowers.

What Is the Best Month To Plant Iris Bulb?

Generally speaking, the best months to plant iris bulbs are from July through September.

If you do it this way, the rhizomes will have the most chance to get in the ground, settle in, and start growing roots.

Depending on the conditions in your area, you might even be able to plant them in October, and they’d still have enough time to grow and bloom by summer.

If given proper care and the right conditions, you can expect them to produce flowers anytime from February to May or June.

The tell-tale sign that it’s time to plant iris bulbs is when nighttime temperatures hit anywhere from 40 F to 50 F and up.

Choosing Iris Bulb Seeds

In case you don’t know, rhizomes are the underground stem from which irises grow.

As mentioned, you will find many options when looking for iris varieties to plant and grow.

The final decision will depend on your preferences and your area’s growing zone classification.

To help with your search, here are the most common ones:

Bearded Iris

Perhaps the most common type, you’ll easily distinguish this variety for its downward-facing petals and its “beard.”

These cultivars can survive in USDA Growing Zones 3 to 10.

Planted in early fall in areas that get full sun, you can expect to grow plants as tall as two to three feet.

Then, there’s the dwarf bearded iris from the same cultivars. This type can only grow up to 15 inches high.

If you want something even shorter, check out miniature dwarfs, which are only eight inches tall.

One thing you might not like about bearded irises is that their foliage will become ugly and ratty when they’re finished blooming.

Dutch Iris

The Dutch hybrid group produces small flowers that are either white, blue, or yellow.

Compared to other types, it doesn’t grow from rhizomes but from bulbs.

It can be as tall as two feet when exposed to full sun and planted in USDA Growing Zones 6 to 9.

Dwarf Crested Iris

No more space for plants that need full sun? Try growing dwarf crested irises instead.

While it can tolerate full sun, it grows best when planted in partial shade.

At just six to nine inches, it attracts bees and hummingbirds when it blooms between March and May.

Originating from the Eastern United States, it grows in growing Zones 3 to 9.

Louisiana Iris

As its name suggests, these are most common in the Gulf Coast area.

They like mild temperatures and slightly sandy, acidic soil and can grow from 12 to 60 inches depending on the hybrid.

Plant them in partial to full sun to grow healthy plants.

These beardless, water-loving hybrids are very hardy varieties and can grow in areas categorized under USDA Growing Zone 4 through 9.

Siberian Iris

Like the Louisiana iris, Siberian irises don’t have “beards.”

They grow best in USDA Growing Zones 3 to 9 and in gardens exposed to partial or full sun.

This variety is easy to grow and maintain and will most likely thrive in regions with temperate climates.

Siberian irises continue to have healthy and elegant-looking foliage throughout the season.

How To Plant Iris Bulb

Whether you’re a beginner or an experienced green thumb, you will find that growing irises is a lot of fun.

Aside from having a sea of iris varieties to choose from, you’ll also like that they are a beginner-friendly perennial plant.

The key to having a lush garden bed of healthy irises starts with knowing how to plant iris bulbs properly.

Here are the steps to planting iris bulbs:

Step 1: Ready the Soil

The first step to growing any plant is knowing the kind of soil where it will thrive at.

As mentioned, irises like neutral to slightly acidic soil.

But aside from that, you have to give each plant good drainage and aeration to prevent the roots from rotting.

Step 2: Plant the Rhizome

To plant rhizomes, make sure that the top is exposed.

The holes where you plant them should only be about four inches deep and around 10 inches in diameter.

You should add a thin layer of dirt on the soil surface only if it gets too hot in your area.

If it doesn’t, adding mulch or covering the rhizome will only encourage rotting.

The rhizomes should be around a foot or two feet apart so that they don’t compete for water, nutrients, and soil.

Step 3: Give Them Water

Once you’ve planted your irises, the next thing to do is to water them.

Newly planted irises need thorough watering.

Give them water generously and then wait a few days before watering again.

How To Water Iris Bulb

Any growing plant needs good-quality water to thrive.

For irises, here’s what you need to do to make sure they’re getting enough hydration:

Step 1: Water As Needed

Usually, the soil around your irises will be dry and ready for watering every seven to 10 days.

Do this either in the morning or at night.

Step 2: Stop Watering When the Weather Cools Down

When it begins raining or snowing, your irises won’t need as much water.

By this time, they would have already been established, so you won’t need to water them until the following summer growing season.

However, if it gets very hot and dry in your area, you may need to continue watering them.

They are drought tolerant for the most part, but irises also need help with hydration in extreme conditions.

How To Grow Iris Bulb

When growing irises, it’s very important that you check each plant regularly to make sure they have the right growing conditions.

Here are tips and tricks that will ensure they grow beautifully:

Tip 1: Keep roots aerated and rhizomes uncovered.

From time to time, check that the rhizomes aren’t covered with organic matter, dirt, or debris.

The soil might also need additional care to ensure it still has good drainage and aeration.

Tip 2: Remove dying foliage.

Browned, dead leaves don’t provide any benefit to your irises, so trim them off when any occurs.

In line with this, cutting the flower stalk before the winter season might also help prevent rotting if ever the flower dies due to extreme cold.

Tip 3: Ready your plants for winter.

If your area gets really cold during winter, you may want to add a thin layer of loose much to protect your irises.

Make sure you don’t add too much, though, as it might cause rot because of trapped moisture.

Tip 4: Use eco-friendly weed killers or herbicides.

As winter ends and spring arrives, remove the mulch you added to protect the soil from extreme cold.

Then, pull out weeds and any grasses from around the base of your irises.

Watch out for slugs and other pests, too.

Tip 5: Give them good fertilizer.

Want to make sure your irises get the nutrients they need?

Try adding in fertilizer, but make sure you pick the right kind and not those high in nitrogen.

Instead, use a general-purpose 5-10-5 or 5-10-10 fertilizer. You can also use bone meal or superphosphate.

Tip 6: Divide your irises so that they don’t compete for nutrients.

Over several growing seasons, you can expect your irises to continue growing and spreading from their roots.

In this case, you will have a full bed of irises in a few years.

Avoid overcrowding by making sure you divide the irises every three to five years.

You’ll know this when the rhizomes start to grow into each other.

How Long Do Iris Bulb Take To Grow?

The answer to this question might not be as straightforward as you’d want it to be.

Spring blooming irises will bloom when the weather turns from cool to warm, but it’s not as easy as that.

Basically, they have to experience up to 15 weeks of 35 F to 45 F temperatures for the bulbs to sprout.

Even if they do meet this requirement, you will also probably have to wait a week or two for them to sprout.

When growing irises, keep in mind that only around 60% to 75% of them will bloom in their first year.

So, don’t beat yourself up if they don’t flower their first year.


New to gardening? Growing iris flowers is a good place to start to develop your green thumb.

Whether you plant bearded irises or those with no “beard,” you’ll find that they aren’t as demanding to care for once they are established.

By then, you will only need to divide them whenever they have become too crowded.

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