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A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Sunday - May 18, 2008

From: Kerrville, TX
Region: Southwest
Topic: Compost and Mulch, Diseases and Disorders, Planting, Herbs/Forbs
Title: Chlorosis in tropical milkweed and asclepias tuberosa
Answered by: Barbara Medford

QUESTION:

I planted both tropical milkweed and asclepias tuberosa. Both are chlorotic and the native milkweed has brown upturned leaves. Could it possibly be too much water? Or what?

ANSWER:

Asclepias curassavica, or Tropical Milkweed, is a native of South America and therefore does not appear in our Native Plant Database. However, here is a Floridata website on it for reference. Asclepias tuberosa (butterfly milkweed) is a native and you can click on the link and read the information on it in our database.

Chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll. Possible causes of chlorosis include poor drainage, damaged roots, compacted roots, high alkalinity, and nutrient deficiencies in the plant. Nutrient deficiencies may occur because there is an insufficient amount in the soil or because the nutrients are unavailable due to a high pH (alkaline soil). Or the nutrients may not be absorbed due to injured roots or poor root growth.

The Asclepias genus usually does not require a great deal of water, but if the soil is not draining well, the roots will be inhibited from picking up the trace elements in the soil, especially iron, and that will result in the plants becoming chlorotic. The major cause of chlorosis is a deficiency of one of the essential micronutrients such as iron or manganese. This deficiency occurs not because the nutrients are lacking in the soil but because they are unavailable due to a high-pH soil. At these higher soil pH levels (6.5 and above) many trees and shrubs are incapable of taking up adequate amounts of iron or manganese. This part of Central Texas has a lot of alkaline soil; however, some compost mixed into the soil or used as a top dressing often will address the problem, providing better drainage, reducing the alkalinity and improving the texture of the soil and permitting access to the trace elements needed.

 

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