Tall and distinctive, pampas grass (Cortaderia selloana) makes a showy statement in the landscape. Sometimes it's almost too showy -- the non-native plant is categorized as invasive in many areas, including parts of California. Pampas grass can also become a fire hazard if left untended. Keep this large plant under control by cutting it all the way back to the ground at least once a year.
Cut pampas grass back in late winter, before new growth appears. In general, pampas grass grows in U.S. Department of Agriculture plant hardiness zones 8 through 10. It grows as a perennial in warmer areas, but it is not evergreen in freezing climates. Still, many cultivars are cold-hardy and can survive in climates lower than USDA zone 8. When cold weather sets in, the foliage and stems dry out, turning brown and becoming a fire hazard. Make room for new growth by cutting it back almost to the ground.
Pruning this plant is not a simple matter. At maturity, pampas grass can reach a maximum average height and spread of 10 feet. Because of the size of pampas grass, power pruners or hedge or lopping shears are most effective in cutting back the plants. Sterilize the pruning tools by dipping them in a solution of 1 part bleach to 10 parts of water, then rinsing the tools before you start cutting. This will help prevent the spread of fungal and bacterial diseases. Protect yourself as well -- even dry, pampas grass leaves have sharp edges, and they will slice easily through your skin if you aren't careful. Wear long sleeves and gloves when cutting back the plant.
Combing Dead Foliage
Pampas grass is a vigorous grower and will grow to its maximum height -- or close to it -- in one season, so cutting it back to the ground won't really limit its size. If you don't have the tools to cut it all the way down, remove the dead foliage from the plant by combing it. Take a small garden rake and use it to grab and pull the dead foliage from the plant. Any dead leaves will easily pull away from the main plant. This will help clean up the appearance of the pampas grass without having to cut it all the way back.
Cutting the Plumes
Pampas grass is best known for its tall, feathery plumes. The striking plumes are often used in dried flower arrangements. If you'd like to harvest the prunes, use lopping shears to clip them off right after they fully open. If you wait too long, they will start shedding, especially in heavy rains or winds.