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The use of geotextiles for landscape weed control.

The Use of Geotextiles For Landscape Weed Control

A major objective of landscape maintenance programs is the suppression or elimination of weed growth. Weeds not only detract aesthetically from a landscape, they also compete with desired trees, shrubs and other plants for space, light, water and nutrients, serve as a habitat for insects and diseases and, in some cases, cause alleopathic (phytotoxic) growth suppression of desired plants.

Weeds are controlled in landscapes using cultivation, hand weeding, mulches (both organic and inorganic), herbicides, physical barriers (newspaper, black plastic, geotextiles) and combinations of all of these methods. Each has its advantages and disadvantages.

Cultivation and hand weeding are labor intensive and therefore expensive and cultivation can damage shallow plant roots. Mulches are expensive, with organic mulches supporting weed growth and requiring replacement due to decomposition. Herbicides require knowledgeable, careful application, with accurate timing for pre-emergence chemicals. Black plastic's nonporous nature can adversely affect landscape plants by blocking water and air movement.

Numerous Field Trials Underway

With an increasing desire among landscape professionals to reduce chemical use, weed control alternatives are being actively sought. Because they are porous, the geotextiles, both nonwoven and woven, are being used as a black plastic alternative. When used for this purpose, they are referred to as landscape fabrics or weed barriers (Figure 1). The majority currently being used are composed of polypropylene.

To date, university reports on the weed controlling capabilities of geotextiles have been limited. Martin, Ponder and Gilliam[5] reported variable weed control from the use of nine polypropylene fabrics, with control dependent on the weed species and the particular fabric. McLean, Kobayashi and Defrank[6] noted mixed results using two organic mulches, one herbicide and one polyester fabric. Powell, Skroch and Bilderback[7] reported that a longleaf pine straw plus a fabric barrier was superior for weed control when compared to longleaf pine straw or pine bark mulch used alone.

Earliest work has reported differences in weed control depending on whether the weeds germinated above or below the fabrics and upon whether or not the fabrics were covered with an organic mulch layer[4]. In addition, while the fabrics may help considerably with the control of annual weeds, they are far less effective against perennial weeds (Figure 2).

All fabric manufacturers recommend that mulch be put atop the fabrics. With fabrics that lack ultra violet light inhibitors, this mulch layer is important to prevent photodecomposition that leads to fabric deterioration and subsequent weed seed germination (Figure 3). With fabrics that are either white in color or lightweight, light passes through the fabrics and weeds grow beneath them, again showing the necessity of the mulch layer.

The problem with covering the fabrics with mulches is the increased weed growth that frequently occurs if the mulches are organic materials. Weed seeds either blow in or are carried in by irrigation water, or may be contaminants of the mulches themselves. The organic materials themselves therefore serve as an excellent growth medium for the weeds.

The deeper the organic mulch layer, typically, the greater the weed control, to a point where over a certain depth (more than four to six inches) any possible positive benefit from using the fabrics is negated[3]. It should be noted, however, that mulch layers exceeding three inches may damage plants by holding too much moisture against their stems and/or over their shallow roots. Therefore, both for the benefit of the landscape plants around which they are used and to get a benefit from using the fabrics, shallow (two-three inches) mulch layers are recommended[2].

If weeds grow in the mulch and their roots penetrate the underlying fabrics and begin to grow in the soil, rapid growth can occur. This necessitates costly hand weeding or herbicide application. If weeds are not pulled or killed when young, the fabric is often torn when weeds are eventually pulled.

To address the problem of weeds growing in the organic mulches atop the fabrics, research is currently underway comparing the use of inorganic mulches (marble chips and lava rocks) versus organic mulches (shredded and chunk pine bark). Research is also being done into alternative fabrics that appear to have greater resistance to root penetration.

Another instance of fabric penetration was seen in the upward penetration of tree and shrub roots. The well aerated, moist environment created by the organic mulch/fabric combination encouraged surface root development. Many of these roots then penetrated the fabrics, especially the nonwoven types. This could be a potential problem if a landscape area needs to be reworked with any regularity or to any significant extent.

Other information that has been collected relative to landscape use of the geotextiles concerns any effect on the soil environment. No significant differences were seen in soil temperature or soil moisture (at a five-six inch soil depth), regardless of fabric type, when the fabrics were covered with organic mulches. Differences occurred only if the fabrics were left unmulched (Table 1), which, as discussed, is not a viable option. The fabrics do not appear, therefore, to have any negative effect on the soil environment created for plant root. Further research is focusing on these effects at shallower soil depths and also when comparing organic with inorganic mulches.


Temperature C [degree]
 No Mulch With Mulch
 June July September June July September
Bare Ground 26 31 23 23 26 23
Black Plastic 28 30 26 22 27 23
Nonwoven 24 28 22 22 27 23

 No Mulch With Mulch
 June July September June July September
Bare Ground 83 40 15 95 94 95
Black Plastic 96 97 97 95 96 97
Nonwoven 93 67 31 95 96 97

(a) Relative soil moisture reading. A reading of 95 equals 25% soil moisture, 60 equals 22% soil moisture, 25 equals 15% and 10 equals 12% soil moisture.

One final observation of possible concern was an increase in vole runs in plots where geotextiles (and black plastic) were used under the mulches. Since voles are herbivores, this could lead to added feeding on the roots of desirable plants, with subsequent tree or shrub stress or death. This phenomenon is likewise being further investigated.

New Uses For Geotextiles in the 1990s

Other current research is focusing on the use of geotextiles as carriers for the application of chemicals (fertilizers, herbicides and other pesticides) needed in the production of quality nursery stock[1].

Many of these chemicals are hand applied, often more than once each growing season, straining an ever diminishing labor pool. If applied by broadcast methods to save labor, extra chemical is applied to the production beds between the containers and to surrounding roads. This leads to excess use of chemicals and increased potential for ground water contamination.

A method has been developed for applying multiple chemicals to container-grown plants all at one time. A "horticultural collar" is being made from two pieces of a geotextile fabric or other material, with the necessary chemicals contained between them (Figure 4). This method will assure that the correct amount of chemical is applied only to the target plant and will eliminate costly multiple applications.

It will also eliminate direct applicator contact with any potentially harmful chemicals. Both the types of materials to be used as the carriers and what chemicals and chemical formulations are best utilized are currently being refined.

PHOTO : Figure 1: Example of nonwoven fabric applied with mulch layer for landscape weed control

PHOTO : Figure 2: Penetration of a nonwoven fabric by a nutsedge, a major perennial weed problem

PHOTO : Figure 3: Weeds growing through holes caused by photodecomposition of a nonwoven fabric

PHOTO : Figure 4: A horticultural collar, made from a nonwoven fabric, for use in distributing chemicals to container-grown nursery stock Literature Cited [1.] Appleton, B.L., and J.F. Derr. 1989. "Use of geotextiles disks for

container weed control." HortScience 25(6):666-668. [2.] Appleton, B.L., and J.F. Derr. 1989. "Combining mulch with geotextiles

for landscape weed control." Proc. Southern Nur. Assoc.

Res. Conf. 34:262-265. [3.] Billeaud, L.A. and J.M. Zajicek. 1989. "Influence of mulches on

weed control, soil pH, soil nitrogen content and growth of

Ligustrum japonicum," J. Environ. Hort. 7(4):155-157. [4.] Derr, J.F. and B.L. Appleton. 1989. "Weed control with landscape

fabrics," J. Environ. Hort. 7(4):129-133. [5.] Martin, C., H. Ponder and C. Gilliam. 1987. "Ability of

polypropylene fabric to inhibit the growth of six weed species,"

Ala. Agr. Expt. Sta. Res. Rep. 5:25-26. [6.] McLean, M., K. Kobayashi and J. DeFrank. 1987. "Weed control

with various mulching and herbicide methods in a new lime

orchard." HortScience 22:151 (Abstract) [7.] Powell, M.A., W.A. Skroch and T.E. Bilderback. 1989. "Landscape

mulch evaluation," Proc. Southern Nur. Assoc. Res. Conf.

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Title Annotation:Markets For Nonwovens
Author:Derr, Jeffrey F.; Appleton, Bonnie Lee
Publication:Nonwovens Industry
Date:Apr 1, 1991
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