A group of perennial dusty miller (Centaurea cineraria) plants developed interveinal chlorosis on the older leaves. The initial assessment suggested that magnesium (Mg) deficiency was the cause because we don't have naturally occurring Mg in our irrigation water. Tissue analysis proved otherwise.
Centaurea cineraria 'Colchester White' is a perennial dusty miller that adds a nice white textured leaf pattern to gardens. While visiting a greenhouse recently, the grower asked about their crop. Overall the plants looked good, but the lower leaves had developed interveinal chlorosis.
Because our bedrock is granite and the surface water is the main irrigation source, it lacks a nutritional punch. If you want to provide calcium (Ca) or magnesium (Mg), you have to include it in your fertilization program. The need to add supplemental Mg results in frequent instances of Mg deficiency appearing late in the production season once the supply from the dolomitic limestone runs low. Therefore, it is a pretty safe bet when one observes lower leaf interveinal chlorosis, that it is a Mg deficiency.
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