Why Is Iris White Instead of Purple?

White iris may take over areas previously occupied by purple iris.

Siberian iris and Japanese iris are the two main categories of iris plants. Both Siberian and Japanese iris come in bearded varieties, which make up the most common selections of cultivated iris plants in yards and parks. The tall bearded iris grows to an average height near 28 inches tall and blossoms in a wide array of colors. Iris may exhibit white blossoms for a variety of reasons.

Dominant

White is the dominant color for bearded iris, although numerous varieties, including hybrids, supply a rainbow of color choices. Iris grows from underground rhizomes, dying back to the soil each year during hard winter frosts. These plants reproduce by rhizome division. While improper soil conditions can cause weaker, purple blossoms to die out, the hardier white plants may continue to reproduce, gradually replacing the areas of purple blossoms with white ones. This may appear as if the original purple iris plants suddenly start to produce white flowers, although the white ones are actually a separate variety.

Variety

Iris varieties that naturally produce white blossoms include cultivars like Cheers, Laced Cotton, Henry's White and Little White. Not only do the white blossoms look different, they have a different scent since the genes responsible for color in iris are the same genes that produce the scent. Prepackaged iris selections may contain a few of these white iris as well as colored varieties. Since not all iris bloom the first year, you may not notice the pale blossoms in your garden until the second season after planting the iris.

Frost

A late spring frost can actually change the color of the developing flower from purple to white. This is not a permanent change and may affect only a few blossoms on the iris plant. Covering plants that contain new flower buds before an expected cold snap can help prevent the flowers developing on a purple variety from turning white.

Care

Properly caring for your iris can help them maintain their vibrant colors. Digging up and dividing old rhizomes every 3 to 5 years will help weaker cultivars continue to provide color in an iris bed. Digging up the dormant plants and cutting apart the rhizomes will produce additional plants the following year. If you notice a higher percentage of white blossoms every year, remove the white divisions from your iris bed while planting the colored selections back in the garden soil.

References

• University of Minnesota Extension: Iris for Northern Gardens
• North Dakota State University Extension: Iris
• C and T Iris Patch: Frequently Asked Questions
• "Botanica's Gardening Encyclopedia"; Susan Page; 2001