The Bay Gardener

by Dr. Frank Gouin

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Landscape Fabric Is Not Invincible

Weeds can find a way

Landscape fabrics are advertised as the solution to controlling weeds in the landscape. What the manufacturers don’t tell you is that if you have Bermuda grass, nutsedge or nutgrass, or pigweed growing in your yard, you will have problems. They also don’t tell you that you should not apply more than one inch of mulch over the fabric.

Depending on the manufacturer, landscape fabrics can be made of woven or non-woven geo-textiles that resist rot. They are designed to exclude light from penetrating while allowing water and air to enter the soil. With light excluded, seeds that germinate beneath the fabric are shaded out. If weed seeds germinate in the mulch covering the fabric, the roots cannot penetrate and die from drought or starvation — providing you do not put too much mulch over the fabric.

However, Bermuda grass spreads by rhizome, and nutsedge spreads by nutlets and rhizomes, all of which can sprout beneath the fabric and penetrate it. These weeds can be in the soil prior to laying the landscape fabric or can invade from the sides.

Pigweed is a problem because its roots are capable of penetrating the landscape fabric and the seeds are capable of germinating in the mulch cover. It is impossible to pull out these weeds by hand without destroying the fabric.

Should these weeds become established in landscape fabric, the only solution is to kill them using a weed killer like Roundup. To avoid causing any injury to your ornamentals, Roundup is best applied with a wick applicator, paint roller or brush. Spraying Roundup can result in plant injury due to drift unless you are using very low pressure and are shielding other plants from the spray.

If you are going to use landscape fabric to control weeds, make certain that these weeds are not present, and never apply more than one inch of mulch over the fabric. Never reapply mulch without removing the old mulch. Allowing decomposed mulch to remain on the fabric will only encourage the growth of weed seeds that blow in. I recommend using only pine bark mulch such as nuggets that tend to dry quickly and not hold water.

Trouble with Weed-and-Feed

Q Unfortunately, I came across your article “How to Grow a Green Lawn — Without Chemicals” [April 23: www.bayweekly.com/year09/issue_17/gardener.html] a day too late. I had put down a Scott’s weed-and-feed. A couple hours later it rained and continued for two days straight. The lawn care representative at the hardware store told me I would have to re-apply the Scott’s. I did so and burned sections of my lawn.

I felt sick about doing this damage and particularly irresponsible for purchasing and applying a product that is considered hazardous to the environment. I will begin to follow your recommendations — starting with getting my soil tested — for keeping the lawn at its most virile to inhibit weed and broadgrass growth. I also have dogs in the yard.

–Catherine Davidson, Annapolis

A I am surprised that you are using weed-and-feed with dogs running the yard.

The lawn care representative did not know what he was talking about in needing to reapply. What the rain did was activate the weed killer, which is mostly 2,4-D and MCPP, pushing it into the soil and into the plant faster along with the fertilizer, so that the second application gave you the results you experienced. It has been my experience that most dealers are salesmen and not lawn technicians.