When To Plant Iris – Planting Guide 2022

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when to plant iris

With roughly 300 colorful species under its name, it’s no surprise that the iris is named after the Greek goddess who rode rainbows.

It’s also among the most popular flowering plants, thanks to the fact that it’s easy to grow, reliable, and rugged.

When to plant iris? Planted at the right time, irises will be strong and established enough to survive the winter. The best time to plant iris is when nighttime temperatures fall between 40 and 50 degrees. It could be anywhere from late summer to the early weeks of fall.

What To Expect When Growing Iris

The majority of the flowering plants that belong to the iris genus are scattered around the north temperate zone.

However, you will find its most beautiful species in warmer climates, with some native to central Asia and Mediterranean regions.

Generally speaking, you can expect your iris plants to thrive if you are located within Zones 3 and 9.

Iris plants need exposure to full sun for at least half the day to produce brightly colored flowers.

Although some species may tolerate partial shade, they will have a hard time blooming. Some won’t likely flower at all.

Depending on the variety, irises will start producing flowers in spring or summer, especially the tall bearded iris.

However, expect your smaller irises to bloom early in spring.

For reblooming varieties, you’ll get to enjoy the beauty of iris flowers first in summer and then again in the fall.

Rhizomatous vs. Bulbous Irises

Rhizomatous vs. Bulbous Irises

Even with so many species, there’s no doubt that you will find an iris variety suitable for your garden.

The trick is making the right choice. To help you with this, let’s start by dividing the many iris varieties into two groups: rhizomatous and bulbous.

To distinguish which ones are ideal for growing in your region, here’s where the two differs:

Rhizomatous Irises

As you can probably guess, these irises grow from rhizomes.

Bearded Irises

The most popular of all groups, it gets its name from the hairs that grow on the center of the fall or the surrounding petals.

These prominent hairs can be colored or white.

Many bearded iris varieties produce more than one flower for every stem. What’s more, they come in a variety of colors.

These common garden irises are hardy. Their leaves are swordlike, and each tall stem will produce three or more blooms.

Beardless

As the name suggests, these varieties of irises don’t have “beards” but smooth falls and require less maintenance.

Some examples are the Pacific Coast, Louisiana, Japanese, and Siberian iris.

Crested

If you have moist soil rich in humus, you will have a better chance of growing crested irises.

Like other irises, though, it needs full sun but can also tolerate partially shaded areas.

Bulbous Irises

Bulbous irises shed their leaves after flowering and will go dormant in the summer.

Among the most common ones are the dwarf iris and the Dutch hybrids.

Dutch Hybrids

These are most likely what you see in spring bouquets. They bloom earlier than taller bearded irises.

Created in the Netherlands, you can expect these hybrids to be sturdier than other varieties.

Dwarf Iris

Got a rock garden? The smaller reticulated irises are the ideal choice if you’d like to grow them in groups or in pots.

However, they need more maintenance than others to prevent overcrowding. Most likely, you will need to divide the plants every few years.

Dwarf irises will bloom around early spring.

How To Plant Iris

If you have the patience to wait for a couple of years, you can start your iris plants from seeds.

In comparison, propagating iris plants, either by rhizomes or bulbs, will give you not only better but quicker results.

As mentioned, you’ll want to do this from late summer through early fall.

Step 1: Pick a spot.

Look for a spot in your garden that will suit your iris plants the most.

It has to be sunny, and there shouldn’t be trees nearby that would block the sun.

Once you’ve decided, start pulling out grass and weeds from the soil.

If you don’t, they will eat away at the nutrients, water, and space that could’ve otherwise gone to your irises instead.

Step 2: Make sure the soil is ready.

First and foremost, you have to check if the soil in your garden is ready.

Again, temperatures have to be around 40 to 50 degrees and the composition neutral or a bit acidic.

Ensure the soil is fertile by adding two to four inches of compost to the mix after tilling the soil to about 12 inches deep to ensure good drainage.

Do this two weeks beforehand to make sure everything is ready for planting.

Step 3: Start planting.

Start by making two rows in the ground with a small ridge in the middle where you will plant the rhizomes.

If you’re from a warmer climate, plant the rhizomes horizontally just below the soil surface, leaving the top exposed.

The goal is to leave the tops partially exposed to the elements. Cover the rhizome thinly and top with low-nitrogen fertilizer to encourage growth.

You can choose to plant the rhizomes alone or in threes, giving each group about a foot or two of growing space.

When planting bulbs instead of rhizomes, start by digging a hole five inches deep.

Place the bulb with the root down and the pointed end up. At most, plant six bulbs for every square foot of soil.

How To Take Care of a Growing Iris

How to take care of growing iris

A garden bed full of irises will need a lot of care while the young plants are still growing.

In that case, here are expert pieces of advice to make sure you give them what they need:

Keep rhizomes exposed.

Bulbs like being planted deep in the soil. However, compared to bulbs, rhizomes need exposure to the elements to dry out.

If you put mulch and cover them, they will rot. It’s also why you shouldn’t overcrowd your iris garden bed. Only mulch in the spring and do so lightly.

Avoid overwatering.

Excess moisture in the soil will most likely cause rotting. While you should water deeply, your soil has to be well-draining.

You’ll only need to water them more frequently during periods of no rain in the summer.

Compared to bearded irises, Japanese, Siberian, and Louisiana irises require more water.

Fertilize at the start of spring.

During spring is when your iris plants will grow quickly. If you want to help speed things up, you can apply an all-purpose fertilizer.

Again, use only low-nitrogen fertilizer on the surface or apply a thin layer of organic mulch to keep them from rotting.

If you’ve planted a reblooming variety, your plants will benefit from the second round of fertilizer after the first blooms.

Basically, you will want to apply fertilizer roughly one month before the plants are expected to bloom.

Remember to use a fertilizer with low nitrogen to prevent rot.

Give them support.

Besides applying fertilizer, your growing iris plants may need structural support in the form of stakes.

This is especially true for taller iris varieties, which could fall over without staking.

Remove flower stems after blooming.

After the blooms have come and gone, it’s time to deadhead your iris plants.

Using a pair of clean garden shears, cut off any brown tips and the flowering stalks all the way down to the exposed rhizome.

Remember to do this only after they are done blooming. Otherwise, the plants will have difficulty generating energy for new growth.

Cut foliage in the fall.

If your iris garden falls victim to a hard frost, remove any dead, spotted, or yellowed leaves afterward.

It is a crucial step to avoid and destroy the eggs of iris borers, a kind of insect that targets and destroys irises.

Protect the plants against the cold of winter.

Cover the rhizomes with about one to two inches of sand to protect them from the cold. Lightly layer with evergreen boughs to provide enough warmth. Do this after the ground has frozen.

Come spring, get rid of old foliage and winter mulch to allow the plant to grow fresh leaves. At the same time, it helps keep Iris borers at bay.

How To Divide Iris

In about two to five years, your iris garden will most likely become overcrowded. Often, it can stress the rhizomes out and cause them to stop producing flowers.

Fortunately, you can remedy this issue by dividing and replanting healthy rhizomes in fresh, fertile soil. Wait until after blooming before doing this.

Step 1: Look for offshoot rhizomes.

Dig up the original rhizomes you planted after your iris plants finish flowering at about mid-summer.

There, you will find that it has produced a few rhizomes of its own.

Step 2: Cut the new rhizomes.

Using a sharp knife, separate the young rhizomes from the mother.

At this time, you’ll also want to discard the original rhizome, which has done its part and will no longer produce flowers.

Check each young rhizome for disease or any kind of rotting, and get rid of unhealthy ones.

Step 3: Trim foliage.

After getting the rhizomes, it’s time to trim the leaves down to about five inches.

Without any leaves, the plants can focus their energy on growing new roots instead.

Step 4: Plant new rhizomes.

If you wish to grow more irises, go ahead and plant the young rhizomes in a freshly prepped garden bed.

Alternatively, you can add new soil to the area where you first planted them and replant them there. You can also give away some to neighbors and friends.

Conclusion

There’s no denying the beauty of irises. Not only is it famous in Japanese flower arrangement but also as the fleur-de-lis of French royal standard.

Aside from its beauty, it’s where orrisroot comes from, used for creating the romantic and powdery essence-of-violet scent.

If you decide to grow them in your garden, pick a spot where you can watch and enjoy the butterflies and birds they will attract.

You can also plant them together with lavender, daylily, phlox, and blanket flower.

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