Plastic weed barriers are a type of inorganic mulch. Usually made of heavy plastic, they are often laid over a garden bed, under 1 or 2 inches of soil or organic mulch. They prevent weed seeds in the soil from germinating and also preserve moisture in the flower and vegetable beds. Annual flower and vegetable beds need weed barrier replacement every one to two years, while a barrier on a perennial flower beds may go several years before requiring replacement.
Wait until fall, when annual plants have died and perennial plants have begun entering dormancy. Trim any perennial plants as usual and remove all the dead and removed plant matter from the garden bed.
Set a tarp beside the garden bed. Shovel all the existing mulch or soil that is on top the weed barrier and place it on the tarp. Take care not to damage any perennial plants in the process.
Cut through the barrier around perennial plants, cutting it away from the plants to avoid damaging them. Pull off the remaining barrier and discard.
Check any drip irrigation lines under the barrier for signs of damage and replace as needed. Add any desired fertilizer or soil amendments to the soil at this time.
Lay the roll of new weed barrier plastic at one side of the garden bed and begin unrolling. Stop when you reach a perennial plant. Cut an "X" shape in the plastic with a utility knife that is just large enough to slip over the plant. Continue unrolling and cutting until the bed is covered.
Smooth the cut areas down and anchor them down with soil. Replace the soil or mulch from the tarp on top the new weed barrier. Add additional soil or mulch as needed so it is a depth of 2 inches.