I would not use black plastic, use newspaper instead. The newspaper (I like to use about 3 or 4 sheets together) will break down back into your soil and the earth worms will love it. I have had no problems when I use newspaper and mulch over it. I have covered soaker hoses with this method and it works great.

I second the newspaper. I have tried black plastic before and it ends up being a real mess over time.

Thanks so much, I will try the newspaper instead : )