Asparagus Harvest

My asparagus reached its third year this April I am really disappointed at only being able to harvest 12 spears from 10 plants.   I did not cut any spears last year, and left the ferns to grow and die down as advised.  I spread well rotted manure in Autumn 2010 over the bed.  As the years go on will I be able to expect more spears, as the space that is being used up at present could be very useful growing something else.  Any advice/views will be much appreciated.

I started my asparagus bed about 7 years ago, and the ten plants are of about 4 different varieties and between 2 and 7 years old (don't ask!)

It's really only in the last year or so that the oldest of them have really come good (bear in mind that your 3" crowns will finish up about 3' across with roots so wide and deep they speak with an Ozzy accent!)

Others may have got them to full production size quicker than this but I can't help thinking that the growers and retailers like to be a bit optimistic about such details! 

The figure I've seen quoted is 15 spears per plant per year, which I think is probably about right for a mature plant (after that you have to let the remaining spears develop into ferns to build up the crowns for next year)

Taking a few spears in the first few years is very tempting but will only delay the development of full-sized and productive crowns in future years.

No (although if your 2 happen to be male and female plants you could get seeds setting.)