Hillside Weed Control

Question:

We’ve had the hill in the backyard weed-whacked and the debris removed. Now the hillside is brown but it still has the roots of the cut weeds. I'd like to place a weed blocking fabric and then plant a ground cover. Do you treat the ground with a weed killer before laying the fabric? 

Answer:

The answer is not as simple as it might seem.
  • The weeds should have been sprayed first before you weed whacked them.
  • A non-selective herbicide, like Round Up will be ineffective 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 not a bad idea to wait and plant in the fall and let the weeds start to grow again. A week to ten days before planting spray the active weeds. I’d encourage the growth by irrigating the hillside in the weeks beforehand.
  • It’s a judgment call on your part whether or not to install the landscape fabric.
    • The landscape fabric is a short-term answer and 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 concludes, 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.
  •  The ground cover depending on the species could reduce this concern as it matures. Controlling the unwanted vegetation after the area is planted becomes more challenging with a non-selective herbicide.
    • These herbicides damage desirable and undesirable plants so you’ll need to be careful when spot treating them.
    •  It’s going to take several growing seasons for the plants to cover the area and you shouldn’t expect much growth this year. To speed thing up, you plant them closer together and apply an annual All Purpose Fertilizer between Mid-February and April.
  •  By planting in the fall, there 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 that can be applied over the top of growing plants as it only kills the plant seeds and 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 instruction, so you’re applying the correct amount of the herbicide for the square footage.