Growing Irises

Growing Irises

By: Brent, Co-Owner, Brent & Becky's Bulbs

The iris is a classic, statement-making show-off that’s hard to beat—it’s no wonder it’s been a garden favorite for centuries. This old-fashioned beauty’s bold blooms contrast with its architectural, sword-like, sturdy foliage.

The name “iris” originates from the Greek word for “rainbow,” which speaks to the many color varieties available. With a wide range of colors, irises make excellent choices for nearly every garden.

Iris Rhizomes

Many of the gorgeous flowers in your garden began as seeds. However, some gardeners choose to grow their favorite flowers from bulbs, tubers, and rhizomes. With the exception of Dutch iris, irises grow from rhizomes.

Rhizomes are similar to tubers in many ways. Rhizomes are thickened, underground stems that grow horizontally, sprouting new sections as they grow. Dahlias and potatoes, for example, grow from tubers: rounded, swollen stems that grow underground. Roots and a stem grow from the iris rhizome, producing the beautiful flowers above ground.

Planting Irises

Irises need a location with good sun exposure (partial to full sun) to power their show-stopping blooms, but they will appreciate afternoon shade in extremely hot climates. They are best planted in the fall to allow the roots to establish before the soil freezes, and they should be planted 12-24” apart to ensure that the plants receive adequate air circulation to avoid disease.

Because iris rhizomes are sensitive to rot, plant in a site with well-draining, humus-rich soil, such as a raised bed or slope. The soil should also be porous enough to allow the roots to grow. If planting in heavy clay soil, add organic matter to the site to ensure the health of the rhizomes.

Growing Irises

Once you’ve found the right spot in your yard with at least 6 hours of sunshine and appropriate soil, planting iris rhizomes is very simple:

1. If you are growing in a container, make sure you choose a size that is large enough to support a fully-grown iris. Select a 6-8” container for a dwarf iris and 12” for taller varieties. The containers should also have excellent drainage.
2. Check your rhizome before planting. We hand-select our rhizomes before shipping for high quality, however, if you’re planting rhizomes from other sources, check for signs of rot, like softening or hollowness.
3. Dig a wide, shallow hole. Iris rhizomes should be planted just under the soil’s surface, with the top of the rhizome showing above the soil.
4. Set the rhizome in the hole horizontally and fan out the roots underneath and around it.
5. Fill in the hole, leaving the top ⅓ of the rhizome exposed. Water well after planting. Once the plant is established, water sparingly to prevent rot. If the top 3” of soil is dry, it’s time to water.
6. Do not mulch, but add some compost around the rhizome. Adding chemical fertilizer can risk adding too much nitrogen which will promote lush foliage growth at the expense of blooms.

Caring For Irises

Once planted, irises are relatively low-maintenance. Water them lightly to keep them hydrated but avoid excess as irises are prone to problems with rot.

If your iris is struggling, it might be that your rhizome is infested with a pest. Borers are the most common culprit. These little, pink grubs tunnel in leaves, making them ragged and streaked, eventually affecting the rhizomes. The bacteria carried by the borers cause the rhizomes to rot from the inside. If you suspect borers, dig the rhizome and destroy it immediately to keep your other irises safe.

Near the end of the blooming season, remove the seed pods but leave the foliage intact after blooming as the rhizome will continue to gather energy for the next growing season. Once the foliage has yellowed, cut it back to help eliminate pests and diseases. To keep your irises blooming well, divide the rhizomes every 3-4 years in late summer or early fall.

Rhizomes can seem intimidating when you first start to grow them in the garden. However, irises are a great choice for a first rhizome, as they are relatively straight-forward while producing stunning iconic flowers. With a few easy steps, your garden will bloom with flawless irises for years to come.