Answer: These plants are frequently described as being more or less pest and disease free. However, there is a reported possibility of rootknot nematode in southern-grown stock that could cause the symptoms. Another possibility is that the plants were allowed to become potbound at some stage of the production process and the resulting encircling roots are now beginning to strangle the plant. In both cases, the only way to tell is to dig up the plant and look at the roots and see. You might also wish to consult with your county extension; perhaps with a visual inspection or a plant pathologist could determine the cause of the yellowing for you. Finally, poor drainage and saturated soil could also cause yellowing from the bottom up. If there has been rain, make sure you are not also watering the plants to create excessively wet soil. I'm sorry I can't give you a more specific answer, but maybe this will help you troubleshoot.
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