Planting Iris Bulbs in Minnesota: What Type of Soil Should You Use?

When planting iris bulbs in Minnesota, it is important to provide well-draining, fertile, neutral, or slightly acidic soil. Loosen the soil to a depth of 12 to 15 inches and mix it with compost or aged manure. This will help ensure that the soil does not become too wet in winter. Generally, bulbs should be planted two to three times deeper than their diameter.

The rhizome should be placed on a ridge in the ground, with the roots facing down into the soil. Space rhizomes 12 to 18 inches apart to avoid overcrowding and promote good air circulation. To make the most of the short flowering period of irises, consider planting them in the middle of a perennial garden, where plants that bloom later can hide the iris foliage. The upper part of the rhizome should be exposed and the roots should extend downwards into the soil.

In very light soils or in extremely hot climates, it may be wise to cover the rhizome with an inch of soil. Firmly press down the soil around each rhizome and then irrigate to help settle it. Avoid planting the iris too deeply as this can lead to failure of flowering and rotting of rhizomes. The most common species of iris is called bearded or German iris (Iris germanica).

This species is prone to certain problems such as iris borer, bacterial soft rot, and fungal infections of rhizomes and leaf spots. Siberian irises are very resilient and produce a circular clump of intense green foliage up to 3 feet tall that looks attractive even when not in bloom. To learn more about different species and cultivars of irises, visit the Missouri Botanical Garden Plant Finder. This website contains information on more than 5000 species and varieties of plants organized into 20 theme gardens dedicated to perennials, annuals, roses, shade plants, herbs, trees and shrubs, as well as a Japanese garden.Irises grow from thick underground stems called rhizomes that are sometimes mistakenly referred to as iris bulbs.