Several ornamental grass species have tenacious root systems and can be a bear to remove once mature, including Pampas Grass. Other than physically digging it out - which is definitely labor-intensive - the only other practical option is herbicide use. Smothering by blocking the plant's light for extended periods can work with smaller undesirable plants, but probably would not be successful or practical here, especially if it's growing close to desirable plants.

Within herbicides, you would need to use a systemic, as these are designed to be absorbed and moved down into roots, where they kill them. Contact herbicides, in contrast, only kill top growth and do nothing to control roots; examples include iron-based and vinegar-based products. Only the death of its root system will keep the plant from returning, though pre-emergent herbicides may be needed separately if seedling Pampas Grasses start appearing in future years.

Recommendations for spraying Miscanthus, another tough non-native grass invading our area, should be applicable here, and they are to apply treatments in autumn and/or late spring. (Pampas Grass emerges late after the soil has sufficiently warmed and won't have foliage to treat earlier in spring.) Multiple applications, spaced-out according to instructions from the product label, will probably be needed until the clump finally succumbs. Use caution with any desirable plants immediately adjacent to the grass as these chemicals are non-selective, meaning they can damage anything else the spray contacts. A shield of disposable cardboard or plastic sheeting could help keep unwanted spray drift off of other plants.

Waxy-leaved plants, which includes several grasses, may also benefit from the addition of a surfactant ("spreader-sticker") to the herbicide solution. These are compounds that help the spray adhere to more water-repellent leaves. If the herbicide you select does not prohibit the addition of a surfactant (check its instructions), using one may help each treatment be more effective. The surfactant's label will give instructions on how much to use.

If you prefer to avoid chemicals when removing the grass, you'll simply have to dig up what you can each time it appears until the regrowth exhausts the root system's energy stores and the plant finally succumbs. It's hard to predict how long that could take, but months to even years is typical for tough weeds.

Miri