Planting iris in the spring is possible, but success depends entirely on the specific type of iris. Many gardeners use the term “iris bulbs” loosely, as the most popular garden types are not true bulbs. Understanding the structure you are planting is the first step toward successful spring establishment. While late summer and fall are the preferred planting times, spring planting is a viable option if certain cultural adjustments are made.
Understanding Iris Types: Rhizomes vs. Bulbs
The iris family falls into two primary categories for gardeners: rhizomes and true bulbs. Bearded Irises, the most common type in home gardens, grow from thick, horizontal stems called rhizomes. These rhizomes act as storage organs, lying at or just below the soil surface, and must be planted to receive warmth from the sun.
In contrast, varieties like Dutch, Spanish, and Reticulata Irises grow from true bulbs. These are teardrop-shaped structures similar to small onions and must be planted completely beneath the soil surface, typically at a depth two to three times their height. This distinction is significant because dormant rhizomes are more forgiving of off-season planting than true bulbs, which may have missed their necessary winter chill period.
Essential Steps for Spring Planting
To maximize success with spring planting, proper site selection and soil preparation are necessary. Irises, regardless of type, require a location that receives full sun, ideally six to eight hours of direct light daily, to develop strong foliage and flower stalks. The planting site must also offer excellent drainage; irises are intolerant of standing water, which quickly leads to rot in their storage structures.
Soil should be loosened to a depth of 10 to 12 inches to allow roots to spread freely and encourage quick drainage. When planting a rhizome, dig a shallow hole and create a small soil mound in the center. Drape the roots over this mound, situating the rhizome so its top surface is either slightly exposed or barely covered with soil, no more than one inch deep.
True iris bulbs, such as the Dutch variety, are planted differently, being fully buried with their pointed side facing upward. After planting, whether it is a rhizome or a bulb, the area must be watered to settle the soil around the developing root system. Consistent moisture is necessary until new growth is visible, though overwatering must be avoided once the plant is established.
Managing Bloom Expectations
When irises are planted in the spring, the plant’s energy is directed toward root establishment rather than immediate flower production. Bearded iris rhizomes will likely not produce a flower stalk until the following year. Spring planting gives the rhizome the entire growing season to anchor itself and store carbohydrates for a strong bloom cycle the next spring.
Some bulbous types, particularly Dutch Irises, may produce a late-spring or early-summer flower if planted very early. However, the priority for all spring-planted irises is ensuring the development of a vigorous root system before summer heat begins. A healthy plant that does not bloom in its first year is better than a weak plant that attempts a premature flower and fails to survive.