Are my Asparagus dead or just shy?

Late last year I planted two rows of one year old asparagus crowns.  So far I've had one solitary shoot out of them.  Should they be up by now, or am I just being too impatient?  Would putting a cloche over the row help to warm the soil up a bit faster?  I've put a manure mulch over the row and tried to keep the soil moist. 

A few other people on the allotment site have said their one year old crowns haven't produced any shoots yet.  However Mr Allotment Rep's wife, who has had her plot since approximately 1938, has a massive bed of mature crowns which are sprouting left right and centre.  I am a new gardener who especially loves asparagus and I'm getting worried that I've somehow killed them off.     My soil is quite heavy, but I did dig plenty of organic material into it beforehand.

Oh well, I guess it's off to Tesco for a year or two more.     Thanks for your reply, I'll stop pacing up and down in front of the asparagus swearing under my breath and let nature take its course.