I was out today planting some bulbs near the Blue Princess and the soil has not dried out, even though we haven't had much rain over the last few weeks. The membrane and bark chips seem pretty good at keeping the moisture locked in. If anything, it's more likely the bed had too much moisture this summer than not enough, and if the others who replied to this post are correct, the hessian will not have helped.

As far as sunshine levels are concerned, from what I have read hollies are OK with sunshine, but many varieties can tolerate shady conditions.