Contamination

• Tar paper does not pose any environmental concerns when used for its intended purpose (under shingles on a roof). But it is made with tar (or asphalt), which is at the bottom of the barrel in the petroleum refinement process. To be safe, do not use it around food-producing plants (like vegetable gardens or fruit orchards).
  
  

Effectiveness

• Tar paper will prevent weeds from growing by blocking any sunlight from reaching them. Since it is designed to be a water barrier for roofing, it will also tend to cause water to pool -- not the best quality in a landscaping fabric. Professional landscape fabric (sometimes called weed barrier) stops the weeds while allowing water to pass through.
  
  

Affordability

• A quick comparison between the cost of tar paper and good quality weed barrier shows that tar paper is less expensive. But with the extra money spent, a good landscaping fabric will out-perform tar paper without any worry of contamination.