asparagus

Does anyone know the temp tolerence of asparagus? we have had -20 degrees here in France and there is no sign of our spears coming through, already a month later than last year, we have scraped away some soil to expose the crowns and there is no sign of any growth. very worried that they have died.

I have an asparagus bed, that is now in it's 4th year.  Last year after the harsh winter we had had, -18 for about 3 weeks, than cold snap after cold snap, I thought I had lost over 50% of my crowns there was no sign from them, but by August there was signs that all were still there. The spears were very small and spindly and turned to fern almost immediately. But then we did have a cool summer last year. So don't dispair, they may still be there, but just slow in waking up.