Dutch Iris Problem

May 2005

Diagnosis: Cold Damage

This problem started showing up on later plantings of the 'Telstar' variety of Dutch iris. The malformed buds show curling, twisting, and streaking, and the problem only occurred with this one variety. Other varieties planted in adjacent beds are asymptomatic. The symptoms are randomly sporadic throughout the bed.

The diagnosis is cold damage. Betsy Hitt, expert flower grower at Peregrine Farm, explains: "It has to do with the stage of development (location of the bud in the stalk) at the time of unusually cold temperatures, or sudden drops in temperature. I think what you have is an interim stage of damage between normal opening and "blasting" or total failure to open. Degree of damage varies because of stage of development of individual plant, length of cold period (how many hours or minutes below freezing) and severity of cold (how far below freezing). Which could explain why one cultivar is affected and not another and also why only one planting (of two or three made from the same lot of bulbs) shows the problem."

Dr. John Dole, cut flower specialist at North Carolina State University, adds that it is very common for cold damage to vary with the stage of growth and cultivar, especially if the cold is just barely low enough to cause a problem for all of the reasons that Betsy stated (above). Mulch would be important for protecting plants during the mid to late winter but as soon as the shoots start to come up through the mulch, they become vulnerable to cold snaps.

This page last updated August 17, 2008.

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