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Monday, September 3, 2012

Preventing Weeds From Growing on Top of My Weed Barrier

Q. Weeds that infested an area of my yard - there is a screen like barrier just under the top soil. My question is what can I do to prevent this in the future without killing the shrubs in this area and what is the best method to eliminate the weeds that do emerge. I pulled and dug these and don’t want to have to do that again in the future.

Weed barrier or geotextile under nursery containers to
prevent weeds from growing
A. I am assuming the screen like barrier may be a geotextile used to prevent weeds that might germinate and grow up underneath and through it. These are frequently laid on the soil surface with a 2 to 4 inch surface mulch applied on top of it. The surface mulch helps to shade the barrier and prevent the germination of weed seeds beneath the barrier. We do not use sheet plastic for this purpose. That is a huge no-no which is another topic in itself.

Weeds such as bermudagrass and nutgrass can grow through the barrier and the mulch but it can be very effective in preventing other weeds. If bermudagrass and nutgrass weeds are close to a source of water such as a drip emitter or a leaky hose they will have no difficulty growing through the barrier and through the mulch.

Weed barrier down. Lets air and water through to the soil.
The other problem with textile barriers covered in mulch is that windblown dirt is trapped by the rock mulch and falls on top of the textile barrier. Over time, this windblown dirt accumulates and forms a soil layer on top of the textile barrier in amongst the rocks. Weed seeds then blow over the rock mulch or might be carried by birds where they fall between the rocks and onto the soil on top of the barrier.

If there is rain or a source of water, weeds will flourish and the textile barrier appears to fail. The barrier has not really failed. The accumulation of windblown dirt on top of the barrier is a major culprit. Weed seeds below the barrier are still prevented from penetrating the barrier and making it to sunlight.

Geotextile barrier
There are three things which you can do to help prevent weeds from getting established. The first is to make sure your sources of water are limited to only where the plants are growing. If you have water that is spraying onto the rock mulch or puddling into open areas from other sources than you are going to have problems. It is imperative to make sure water is contained in the area where plants are growing.

Secondly, it is best that mulches are deep. A 4 inch layer of mulch is much more effective at controlling weeds than a 2 inch layer. Coarse mulches are more ineffective at controlling weeds than fine mulches. By a coarse mulch I mean rocks that are at least 1 inch in diameter.

          Thirdly is the point you are probably not going to like and that is staying on top of weed growth. We have an old saying as gardeners that basically says one year of weeds leads to seven years of weeding. This just means that if you fail to control weeds in your garden area and let them go to seed then the seeds released by these weeds will lead to seven years of weeding.

It is so very important to stay on top of your weeds and get them removed before they form flowers. There are several types of garden hoes that are very effective. For bare soil or very fine mulch I like the diamond hoe. For larger mulch pointed hoes or even a shovel works well. If the weeds are relatively large, spraying the area with water from a hose and hand pulling weeds about 15 minutes later is very effective as well.
Black plastic when laid under rock starts to poke through
in a couple of years. Very ugly. Black plastic is a
temporary mulch and rock is a permanent mulch.

          To aid the gardener chemical companies have developed weed killers that can kill seeds as they are germinating or kill the plants after they have grown from seeds. Many of them are very effective however you are applying and unnatural chemical which is potentially, and in varying degrees, dangerous to other plants, animals and our environment.

          Check with your local ordinances but there are devices which use fire to control weeds. These frequently operate off of LP gas with some sort of torch. These are also potentially very dangerous and should be used with extreme caution.

          In a nutshell, there is no magic bullet except to make sure water goes where you needed to go, increase the depth of your mulch layer and stay on top of your weeds and do not let them go to seed.

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