My purples started coming up about a week and a half ago, the jerseys started last week. Slowly though, we had 4 or 5 so far, from about 16 roots. I fertilized about 3 weeks ago, with corn meal to help prevent weeds, and that may have helped?
Location may also make a difference? Mine is on a raised bed, high up on the yard in a corner protected by privacy fencing, it is a fairly warmer part of the yard and gets full sun.

Disclosure: I am a newbie at asparagus this is my second year. :-)

HTH,
Yara

Might just be a little early for you. Mine is coming up, but I live in a warmer zone. Are the crowns getting plenty of water? I find that mine respond with delight to a good soaking.