A Way to Control Nut Grass

May 8, 2009 at 11:50 am Leave a comment

 This information on getting rid of nut grass (Purple nutsedge or Cyperus rotundus) comes from a C/T/H/A/R (College of Tropical Agriculture and Human Resources—University of Hawai’i Manoa) publication.

This is from removing from ornamental areas but seems appropriate for organic veggie gardens too—if you have 2-4 months.

 Weed cloth, or woven black polypropylene weed mat, can be effective in suppressing purple nutsedge when used properly. It is porous to air and water and can be an effective tool for reducing underground tubers without the use of chemicals or tedious hand-weeding. It is a very durable material that can be re-used many times if handled carefully to avoid making holes by tearing. Using weed cloth against purple nutsedge requires that the garden area be fallow (not planted or tilled) for a period of 2–4 months. After the last crop is harvested, remove all plant residues by mowing or rototilling, and cover the planting area with the weed cloth. The method of securing the cloth to the soil is crucial in preventing purple nutsedge penetration through the weed cloth. The preferred securing method is to use long (10–12 inch) spikes fitted with a large flat washer. These spikes secure the weed mat to the ground but should not be used to pull the weed mat too tight. There should be enough slack to allow some air space between the soil and the weed mat. The worst way to secure the weed mat is to use rocks, soil, or other heavy objects. When the weed mat is held tightly to the ground, purple nutsedge shoots can push through the fabric.

With the weed mat properly in place, purple nutsedge is induced to sprout by generous and frequent watering. A new weed mat tends to repel water, but after a 2–3-week exposure to full sunlight, shrinkage occurs and water can pass through the material. As the purple nutsedge germinates, it pushes the weed mat upward, as if it was inflating it. The purple nutsedge grows so fast that when the pointed tip of the leaf blade gets caught in the weave of fabric, the rapidly elongating leaf blade starts to crinkle up behind it, and penetration of the cloth is thus prevented.

The weed mat must remain in place long enough for weeds to germinate below it and die from lack of sunlight. After several cycles of weed growth and die-back during the 2–4-month period, the weed mat can be removed and the garden replanted. Most of the weed propagules (including purple nutsedge tubers) will have tried to emerge and died.

When the plastic is removed, it is important not to disturb the soil unnecessarily. Cultivation brings up lower layers of soil that will likely contain viable weed seeds and purple nutsedge tubers. Mulching the soil surface after removing the weed cloth will help to suppress any weed seeds remaining in the soil and slow nutsedge germination by preventing increases in soil temperature.

Download the CTHAR document.

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Entry filed under: Community Gardens, Gardening & Agriculture, Home Gardens, Hui Gardens, School Gardens.

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