Answer: This (Eryngium maritimum) is generally considered a tough garden performer as long as it has full sun and very well drained soil. In my experience it also does best in a soil that is not terribly rich. It is possible that the drainage is less than perfect and they in fact "drowned", especially if you have a heavy soil. If the survivor happens to be in a slightly raised position or in a spot that receives less water, I would suspect drainage. A related plant, E. giganeum is actually a biennial and would die shortly after blooming, so that might be another possible explanation. I'm sorry about your plants!
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