Elegant and easy care, Iris bulbs are a colorful addition to gardens and landscapes. These versatile plants can be incorporated into perennial beds and naturalized areas or planted en masse. They’ll add pops of color to spring and summer gardens—as well as make eye-catching arrangements. There’s a reason these beautiful flowers are the subject of paintings and photographs.

About Iris Bulbs

There are two basic types of irises: the bulbous irises, such as Dutch iris and Dwarf iris, and the perennial iris, such as German iris, Japanese iris, Louisiana iris, Siberian iris and the Yellow Flag iris. To learn more about the different types of irises, read our Types of Irises Blog.

When to Plant Iris Bulbs

As a general rule of thumb, iris that are grown from bulbs are planted in the fall, while iris that are grown from roots (often listed as bareroots), are planted in the spring. The German Iris is the exception to this rule.

Traditionally in the United States, the German Iris is planted in late summer and fall. However, K. van Bourgondien also offers German Iris for spring planting. Here’s how they are able to do this: for spring-planted iris, they receive irises from a grower in the Netherlands where the growing season is slightly different. They harvest iris for shipping in the late winter and early spring. Both the spring-planted and fall-planted German iris will perform the same. It just gives gardeners more options.

Timeline for Iris to Grow

Iris grown from bulbs (Dutch iris and Dwarf iris) will bloom the following spring and summer. You can expect blooms from irises grown from roots and rhizomes (German iris, Japanese iris, Siberian iris and Louisiana iris) often the year after planting—and the show will get bigger and better in the coming years. Roots and rhizomes are usually divided every 3-5 years.

Where to Plant Iris Bulbs

If planting Dutch or Dwarf Iris bulbs, select a site that will receive full sun during their bloom time. Because Dwarf Iris bloom before many trees leaf out in the spring, they can be planted in areas that may become shaded by foliage in the summer.

Perennial iris like full sun, but can also tolerate partial shade. They fit well into perennial flower beds and really shine when planted in large groups. Japanese, Louisiana and Siberian Iris also thrive in damp soil and often are grown near ponds, water features and streams. All iris benefit from well-drained soil.

How to Plant Iris Bulbs and Perennials

When planting Dutch iris bulbs, dig a hole about 4 inches deep and place the bulbs 3-6 inches apart. Avoid using harsh synthetic fertilizers or fresh manure. Instead, we recommend using K. van Bourgondien 100% Natural Bulb Food. When planting Dwarf Iris, plant 2 inches deep, 3-4 inches apart in clumps of 4-6.

When planting iris bareroots or rhizomes like German, Japanese, Siberian or Louisiana iris, plant horizontally with the roots going down and with the eye just below the soil surface. Do not mulch over the rhizomes, as the rhizome likes to be exposed to the sun. Mulching can also create moist conditions that cause the rhizome to rot. The plants can be fertilized lightly in the spring using K. van Bourdondien 100% Natural Perennial Food. When planting perennial iris, dig a hole that will accommodate the roots and position the plant so that where the roots meet the stem is about 1 inch below the soil surface.

Iris Care and Maintenance

Most iris are low maintenance. Some gardeners mulch around iris bulbs to control weeds. Iris can be lightly fertilized (we recommend using natural plant fertilizer) annually.

Iris rhizomes are usually divided every 3-5 years.

Prune Iris in late summer or early fall when the foliage starts to fall over (if this has not been done earlier). With a sharp knife, cut the foliage 8-10″ above the soil level. Trim the plant into a fan shape.
Carefully dig up the old clumps. Divide rhizomes with a sharp knife. To avoid spreading disease, dip the knife in rubbing alcohol or a 20% solution of household bleach between each cut. Discard the oldest (center) part of the rhizome. Check for evidence of disease or borers. Destroy (do not compost) any infested rhizomes.
Make sure each new division has a strong root section and a single fan of leaves. Dust the cut surface with powdered sulfur and allow to dry for 1-2 days. The sulfur acts as a fungicide and helps avoid problems with disease and pests.
Replant the horizontal rhizome with the top 1/3 – 1/2 of the rhizome showing above the soil. Plant with the fan of the leaves pointing in the direction you want the plant to grow.

Iris Dos and Don’ts

Several basic dos and don’ts apply to most of the rhizomatous Iris. Exceptions are noted in each variety description on the product page.

Plant Iris in full sun.
Plant Iris in well-drained soil.
Plant the rhizomes horizontally; leaves go up, roots go down. Fertilize lightly in the early spring.
Never plant rhizomes more than 1″ deep.
Do not mulch over the rhizomes.
Do not apply fertilizer directly to the rhizome.

Tips and Tricks

With a few tips and tricks, you can enjoy iris for years. Here are a few simple tips:

The foliage on iris grown from bulbs should be allowed to fade naturally and should not be cut. The foliage is key to making food for next year’s bulb.
After blooming, German Iris prefer drier soil and good air circulation. They thrive in borders and mixed perennial beds. The foliage should not be cut off before midsummer
If planting iris near water features, consider Japanese, Siberian or Louisiana iris because they don’t mind moist soil.
Iris make spectacular cut flowers, so consider growing enough to enjoy in the garden and cut-flower arrangements.