Landscape Fabric For Weed Control

Question:

We've had the hill in the backyard weed-whacked and the debris removed. The hillside is brown, but it still has the roots from the cut weeds. I want to cover the area with a weed-blocking fabric and plant a ground cover. Do you treat the ground with a weed killer before laying the fabric? 

Answer:

  • The answer is more complex.
  • The weeds should have been sprayed first to kill the roots before you weed-whacked them. 
  • A non-selective herbicide, like Round-Up and similar herbicides, will be ineffective if sprayed on the bare ground. It will not kill the remaining roots. These products require plants to be leafed out and actively growing. So, it's a good idea to wait and plant in the fall and let the weeds start to grow again. You could speed things up by watering the area.
    • A week to ten days before planting, spray the actively growing weeds. It's a judgment call on your part whether or not to install the landscape fabric.
    • The landscape fabric is a short-term answer, not a long-term solution for weeds. It will only control the unwanted vegetation and dormant weed seeds below the fabric. You should also cover the fabric with a two to three-inch layer of mulch to shut out the light, preventing the weeds from growing. However, deep-rooted perennial weeds would penetrate the fabric or barrier in time.
    • After the rainy season, the weed seeds from the seasonal grasses and plants will blow in and settle in the mulch.  They germinate with the winter rains or with conventional sprinklers but not necessarily with drip irrigation.
  •  Depending on the species, the ground cover could reduce this concern as it matures. Controlling the unwanted vegetation after planting the area becomes more challenging with a non-selective herbicide. These herbicides damage desirable and undesirable plants, so you must be careful when spot-treating them.
  • The plants will take several growing seasons to cover the area, and you shouldn't expect much growth this year. To speed things up, you plant them closer together and apply an annual All Purpose Fertilizer between mid-February and April. Planting in the fall shouldn't be much of a weed issue next spring.
  • To prevent weeds the following year, I'd apply Monterey Impede to control the weed seeds in the late fall. Monterey Impede is a pre-emergent herbicide used over the top of growing plants as it kills the plant seeds, not any plant with a root system. In addition, Impede requires moisture to establish the barrier.  This isn't a problem if you're using conventional sprinklers, not drip, because the barrier needs to be established over the entire area.
  • You'll then need to wait and apply Impede just before the first significant rains of the season. Once the weeds start to germinate, it's too late. Also, read the instructions to apply the correct amount of the herbicide for the square footage.