What does celery like?

Growing good celery is difficult.  I paid close attention to achieving top-notch soil fertility in the main area where I transplanted celery, this year.  Celery loves water, and as this year provided about the wettest May and June in recorded history, I expected the celery to be excellent.  It was not.  Most of the plants were small and tough and they bolted early.  To my surprise, the only celery plants that really thrived were planted in a portion of the garden that received so much rotted horse manure that the organics level was of the charts.  Most plants in this part of the garden (for example Swiss chard) did really poorly, but the celery loved it.  I am guessing it is my heavy clay soil that discourages the celery.  Apparently incorporating otherwise excessive levels of organic matter improves the soil drainage sufficiently to suit celery.