Spider grass is the common name used in reference to two different plants. Most commonly, the term refers to Aristida ternipes Cav. and its various cultivars. However, the term can also describe another perennial grass, Liriope spicata, or creeping lilyturf. The removal procedures for both plants are identical. You can choose to dig it up and remove it by hand, but many gardeners find it easier to use an herbicide to get the job done.
Select a post-emergent herbicide from your local garden store or use one you have at home. You will also want to choose an herbicide that is "selective" so as not to disturb other plants in the area. Glyophosphate, the main ingredient in the product Round-Up, is a particularly effective herbicide that becomes chemically inert when it reaches the soil. This means it will not travel through the soil to other plants' roots.
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Find a delivery system for the herbicide. Most herbicides are delivered via sprayer and applied to the leaves of the plant, while others are placed in the ground. Choose a post-emergent herbicide that is ready to use or one that you can mix with water in a sprayer.
Mix the herbicide according to the instructions on the package if you did not choose a ready-to-use variety. Be careful and thorough when mixing herbicide to avoid harmful chemicals.
Choose a sunny day without a lot of wind and without rain in the immediate forecast. Timing is crucial for a number of reasons. On windy days, the spray can be blown off course and fall on unintended targets, such as nearby plants. The rain-free period is also important because it ensures the chemical will have enough time to dry on the leaves and be absorbed into the plant.
Apply post-emergent herbicide to the foliage of the spider grass. The herbicide should contain instructions regarding how much to use on a particular plant. You have applied enough herbicide when the leaves are covered and the product lightly drips off the edge of the leaves.
Store leftover herbicide properly and monitor the plant. Spider grass, especially if it is the Liriope variety, is an extremely tough plant that may require more than one application to kill. However, herbicides, especially commercially available varieties such as Round-Up, will kill any plant as long as it is mixed and applied correctly. Reapply the herbicide weekly or biweekly until you have achieved the desired results.
You can use a combination of pre- and post-emergent herbicides if you are concerned the plant is going to come back the next season, although it is generally not necessary to do so.
Carefully follow mixing and storage instructions to avoid health problems.