Thinking about spring planting

[dennysfishroom]

With nice days sneaking in occasionally now, I've started to think about my spring planting. I've got several raised beds that I've been thinking about reworking. They are made from landscape blocks, but seem to really need a lot of watering. Any comments on possibly putting down plastic sheeting over the first layer of blocks to form a catch basin for water, and then replacing the upper blocks and soil? I'm wondering if a 4" catch basin would retain the moisture and wick it up into the soil for the plants? Denny