Iris Planting and Growing Tips

Irises are relatively easy-to-grow perennials with a beautiful burst of elegant flowers available in a variety of colors and shades, which makes them a perfect choice for many gardeners. Let's explore the best way to plant, grow, and care for popular iris varieties.

When to Plant Iris Bulbs

Just as different varieties of iris bloom at different times of year, the planting time for irises varies by species. The best time to plant bearded iris, a traditional bulb, is in fall, when you plant other bulbs like tulips and daffodils. Bulbous flowers need a cold period to activate their growth, so these can safely stay tucked underground during the harsh winter weather before sprouting in spring.The best time to plant most beardless irises, like Dutch irises, is also in fall. Dutch irises, like bearded irises, grow from bulbs and require a cold period to bloom. Try planting these smaller bulbs in early fall-after the weather cools but before the soil becomes extremely cold. These bulbs will need cooler, but not freezing, temperatures to settle into their new home before winter.

Japanese and Siberian irises differ from other irises in that they grow from rhizomes, not bulbs. Rhizomatous perennials should actually be planted in springtime, as these more tender root systems need to become established before the high heat of summer or the cold of winter. Plant Japanese irises when you plant your other spring-planted perennials, like dahlias or gladiolus.

Where to Plant Irises

Iris are such versatile plants for landscape designers, thanks to their varied sizes and the array of colors in which they bloom. As long as you have a sun-soaked, well-draining location, iris bulbs and Japanese iris rhizomes will happily take root in your garden!

Tall bearded irises grow best in well-cultivated, well-draining soil, and prefer bright, sunny locations. Due to their height, tall irises make a lovely back-of-the border display. Some gardeners use bearded iris as statement plantings, creating a naturalized clump to stand alone at a building corner, or near a mailbox. Tall irises are great foils to a low-lying garden, adding height and long-lasting interest.

Dutch Iris prefer bright, sunny locations but can live in partial shade. Shorter iris varieties can be planted in front of taller irises for an all-iris cutting garden, or can work well in front of roses or taller perennials. Because Dutch irises have a nice, long bloom time, their blooms can cover the fading foliage of early-spring bulbs.

Japanese irises and Siberian irises can withstand the most shade out of the iris family. These low-growing, butterfly-shaped flowers do need well-draining soil, but they work well on patios, under trees, or in containers. Japanese Iris are also a favorite water plant grown in containers in pond shallows. Siberian iris can be planted in part shade or full sun. They tolerate the cooler weather and can be planted in moist soil areas or even around ponds.

How to Grow Popular Iris Varieties

Iris varieties are all relatively easy-growing plants, but care does vary between bulb-grown irises and those grown from rhizomes. Luckily, the differences are fairly easy to remember, and any gardener with experience in both bulbs and rhizomatous perennials will recognize the difference between these two groups.

Growing Bearded Iris

The best time to plant bearded iris is in autumn, when you place other fall-planted bulbs. If you have clay-heavy soil, add some coarse sand and humus. A good rule of thumb for bulbs is that they need two times their own height of soil above them-so, dig each hole three times as deep as the bulbs, and place your bulbs with the tip facing up. Backfill the hole, and water the bulbs in well. Most bulbs require about an inch of water per week through the growing season, so give your irises a good drink during dry spells. Many reblooming German irises will bloom all season, so keep your plants well-watered, fertilized, and upright-consider using stakes for some very tall iris varieties.

Growing Dutch Iris

Growing Dutch iris requires plenty of light and good, well-aerated soil. Plant Dutch irises about two inches deep in the soil in early fall, leaving approximately four inches between each bulb. In spring, fertilize your irises right after they sprout. Water generously through the growing season, and cut back on watering after the flowers bloom. Leave the foliage on your irises until it begins to brown and die back naturally.

Growing Japanese Iris

Japanese iris require high soil moisture and a fair amount of feeding throughout their growth period. Japanese irises appreciate rich soil so try planting them in moist soil amended with compost and peat. No lime or alkaline additives needed for these plants! Wait until you see new growth before fertilizing, then feed again just before the flowers bloom. Divide your Japanese irises every three to four years.

Growing Siberian Irises

Siberian irises can be planted in springtime, in rich but well-draining soil. They prefer full sun, but can handle some shade. Plant your Siberian iris rhizomes a few inches deep, and water them in well. Siberian irises tend to require more moisture than other iris types, especially as they become established, so keep the soil consistently moist for their first year or so. Siberian irises should be fertilized with a nitrogen-rich soil in spring and again after the blooms are spent.

How to Care For Irises

One of the reasons irises are so popular? They're very easy to care for. Winterizing irises and keeping them fed isn't a series of whole-day projects—just a few simple tasks to incorporate into your regular gardening routine.

Fertilizing

Irises don't require a great amount of fertilization. However, a small serving of specially-designed iris fertilizer can make your display grow even stronger and healthier. Breck's® Iris Lovers All-Natural Iris Food uses a 4-4-2 ratio of nitrogen, phosphorus and potassium, respectively. Nitrogen is vital for healthy growth, but too much can cause soft, disease-prone growth. A small dose of phosphorus is useful when producing flowers and developing roots, and some potassium helps bring out those rich, vibrant colours that make irises so lovely.

Winterizing Iris

Wait until the foliage of your iris plants dies back naturally—cutting too early will weaken the plants. Apply low nitrogen fertilizer like Breck's® Iris Lovers All-Natural Iris Food and water in. Gardeners in cold regions may opt to mulch over iris plantings before winter, to protect the root systems from damage. Thawing and melting can cause "frost heaving," meaning the soil contracts and can actually push bulbs up. An added layer of mulch will prove helpful in that case too.

How to Divide Iris Plants

Over time iris clumps become crowded and the blooms may suffer. Luckily it is easy to spread out your irises and encourage new growth.

Iris grown from rhizomes can be divided in late summer. Carefully lift the entire clump with a garden fork, then cut apart the new, younger sections from the original center rhizome. You may want to let the rhizomes dry in the sun for a day before replanting. Discard any rhizomes with no buds or roots.

Irises grown from bulbs, such as German bearded irises, can be separated just like other bulbs. In the fall, pull the bulbs up with a spade, then look for smaller "bulblets" on the sides of the parent bulb. Remove those gently, and replant the original and new bulbs where desired.

Common Pests & Diseases That Affect Irises

Bearded iris are more likely to suffer from borers and grubs than root-based iris-pests just find bulbs irresistible. Bulb mites and irises borers may be the cause of rotted iris bulbs, so check for holes on failed bulbs. If you see them, look for a commercially available insecticide to treat borers. If there's no sign of damage to the bulbs other than rot, you may have an issue with wet soil.

For rhizomatous irises and bulb-grown irises alike, caterpillars and aphids can be leaf-chewing pests. Use neem oil to prevent damage from these bugs, and, if you spot just a few, you can remove them with a strong spray of water from the hose.

Slugs and snails are also enemies of most bulbs and perennials. Diatomaceous earth can keep these slimy pests at bay, or try using a beer trap or slug repellant.

Iris Growing FAQs

Do Irises Need Full Sun?

Most irises will bloom best in full sun, although Japanese and Siberian irises can withstand partial shade. Taller irises may bend toward the sun, and may flower less in lower sunlight. Try to provide your irises with at least six to eight hours of sunlight each day.

When do Irises Bloom?

Different types of iris grow at different times!

Tall bearded irises bloom in spring, and reblooming varieties bloom again throughout summer and fall.

Dutch, Spanish, and English irises flower from mid-spring to midsummer. These shorter irises are great for covering up faded blooms from your spring bulbs.

Japanese and Siberian irises are a little shorter-blooming than irises grown from bulbs, but they can flower from mid-spring to midsummer.

Many iris varieties are reblooming, or offer long bloom times. You can really carry your garden through the season with irises.

How Many Iris Bulbs Can You Plant Together?

Iris bulbs are great for naturalizing! While irises grown from rhizomes—such as Japanese or Siberian irises—can be picky about spacing, bulbs typically only need a few inches of space. Any number of iris bulbs can be planted together. Just divide your iris bulbs when they become crowded or flowering is limited.

Should Iris Bulbs be Soaked Before Planting?

You don't need to soak bulbs before planting. For irises grown from rhizomes, soaking may make the roots a little more pliable for planting.

Planting Video for Iris Rhizomes

Download the Iris Planting Guide