No blanching is required, but be sure to thoroughly rinse each rib. You'll then slice the celery. Nice thin, uniform thickness slices work best, about 1/8" or so. (I use a food processor with a slicing blade to prepare the celery.)
Once you have a bowl full of thin slices, spread them out on your dehydrator trays in a single layer. You'll want to use screens or fruit roll inserts, a little overlapping of slices is OK. There is no need to meticulously arrange each individual slice!
Process the celery at 135 degrees for about 6-8 hours, depending on the wattage of your dehydrator. You may wish to rearrange slices about halfway through processing time to ensure even drying.The finished product will be crisp, and easy to crush, and slightly brighter green than the fresh celery.
Store your dehydrated celery in a clean glass jar with an airtight lid in a dark, cool, dry place. Add an oxygen absorber for long term storage. 2 bags of celery will fill a pint sized jar.
Dehydrated celery is especially convenient for throwing in homemade soups, and embellishing box mix stuffing (along with dehydrated mushrooms!). It's also important to have for homemade dry mixes.