What diseases should I be looking for outside of the normal ones like aphids, scale, rust, black spot, etc. ? Have I planted too late in the season?
Certified GKH Gardening Expert
Celery is normally planted once daytime temperatures are around 50-60 degrees F. Also, the plant needs at least a soil temperature of around 59-60 degrees F. This article will help you with growing celery: https://www.gardeningknowhow.com/edible/vegetables/celery/tips-on-how-to-grow-celery.htm
Here is info on both growing this plant and common issues/treatments: http://harvesttotable.com/2009/06/celery_growing_problems_troubl/