Thanks Sandy, I think I might do as you suggest. What have I got to lose? I was watching BBC Gardeners World and the moderator there said that if asparagus doesn't get off to a good start within the first couple of years, there's no point in continuing trying. In other words, tear it out and start over. So it looks like the purple asparagus does tend to produce fewer but thicker stalks? Hmm. Not sure that's a bonus. I think I'll go out and cut down the one purple that has produce a ginormous stalk and see what happens.