Answer: I suspect it's a disease causing the problems. Common celery diseases include early and late blight, which begin as small dots on the leaves, and pink rot, which shows up as water-soaked stem spots and white or pink coloration at stalk bases. Crop rotation is the best control.
Distorted leaves and cracked stems can indicate a boron-deficient soil; correct by spraying the plants with liquid seaweed extract every two weeks until symptoms disappear.
I'd continue to rotate the crops each year and try the supplemental foliar feeding to see if that improves next year's crop. You might try 'Giant Pascal' next time. It's a blight-resistant cultivar that may prove to grow and produce better for you.
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