Marigolds suddenly dying

I have a garden bed with marigolds along the edge and they are all dying. The other flower in the bed are fine - iris, carnations, day lilies. They get watered equally, obviously get the same amount of sun - it's a bed only about 2 feet deep. I planted the marigolds after pulling up a whole weedy patch of violets. They had been growing fine. After I pulled them up I transplanted the iris to this bed, and edged it with the marigolds, which had previously been in a terra cotta planter. What could be causing this?
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wrote:
Hi You probably lost too many roots when you transplanted the Marigolds.
Derryl Calgary, Alberta.

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