Michael,

Thanks for contacting us about using landscape fabric as a weed barrier under flagstone. You are correct that research indicates it’s not an effective weed barrier after about the first year. Soil and weed seeds blow in and settle in between the stones (or rocks, or mulch, etc.) and soon weeds are growing on top of the fabric with roots finding their way beneath the fabric making them more difficult to pull and/or treat. Any exposed edges of the fabric can become frayed and unsightly over time. The weave of the fabric can plug up making even good quality fabric not permeable, creating a lack of oxygen for tree roots and microbes (becoming anaerobic).

Weeds are going to find their way in either way.

There are options for what you use to fill the spaces between the stones (sand, gravel, mulch, groundcover plants, mortar, etc.). Polymeric sand can last as well as help with the weeds. Read up on it. I first saw it used in a patio setting that used large slabs of our native flagstone at the Gardens on Spring Creek in Fort Collins.

Stay cool!

Karin