Pampas grass, known by its botanical name Cortaderia selloana, is a large, perennial ornamental grass prized for its dramatic, feathery plumes and imposing size in the landscape. Native to the South American grasslands, this plant forms dense, arching mounds of foliage that can reach up to ten feet tall and wide. To maintain its health, vigor, and characteristic fountain-like appearance, a regimen of trimming is necessary each year. This annual maintenance prevents the buildup of old, dead material, which can eventually choke out new growth and leave the center of the plant looking sparse.
Seasonal Pruning Timing
The annual, heavy cutback of pampas grass should be performed in late winter or early spring. The ideal window is after the threat of a hard frost has passed, but before the plant begins to push out its new season’s growth. Cutting the old canes back too soon, such as in the autumn or mid-winter, removes the natural insulation the dormant foliage provides to the crown. This exposure can leave the plant susceptible to freeze damage in cold climates.
The stems of Cortaderia selloana are hollow, and pruning them in autumn or early winter creates open channels where moisture can collect. This trapped moisture can lead to crown rot and introduce fungal issues, weakening the plant before spring arrives. The goal of the major cutback is to clear the way for the current year’s foliage and plumes, which emerge as temperatures rise.
Performing a heavy cutback in the middle of summer is ill-advised for horticultural reasons. A summer cutback removes the current season’s developing plumes, which are the plant’s most desirable feature, blooming from late summer into fall. Radical pruning during the peak growing season places undue stress on the plant, forcing it to expend energy on regrowth instead of focusing on plume production and root development.
Techniques for Performing Heavy Cutbacks
Because the foliage of pampas grass has finely serrated, razor-sharp edges, safety preparation is necessary before beginning any heavy cutback. Gardeners should wear protective gear to prevent skin lacerations and eye injuries:
- Thick leather gloves
- Long sleeves
- Long pants
- Protective eyewear
The density of a mature clump necessitates heavy-duty tools such as long-handled loppers, hedge shears, or a reciprocating saw. For large plants, some gardeners use a chainsaw to cut through the woody base.
A highly effective technique is to use heavy twine, rope, or a bungee cord to tie the entire clump tightly together before cutting. This bundling pulls the sharp foliage away from the center, making the base of the plant more accessible and creating a manageable bundle of debris. Once secured, the foliage should be cut straight across, leaving a tuft of old growth approximately 6 to 12 inches above the ground. Cutting to this height ensures that the crown, the point from which new growth emerges, is not damaged.
After the main cut, inspect the center of the plant. Any remaining dead, brown material or debris should be carefully raked out or pulled away from the crown. This final step improves air circulation and sunlight penetration, stimulating vigorous, healthy new shoots. Following this radical pruning, a balanced, slow-release fertilizer can be applied around the base to support the strong flush of spring regrowth.
Light Maintenance During the Growing Season
While heavy pruning is confined to late winter or early spring, lighter maintenance is appropriate during the summer growing season. These activities are aesthetic and keep the plant tidy without compromising its structure or health. The primary task is deadheading, which involves removing the spent plumes or seed heads after they have lost their visual appeal.
Removing these old flower stalks helps prevent unwanted self-seeding, as pampas grass can be aggressive in some environments. This trimming targets only the tall, slender stalks of the plumes, leaving the main body of the foliage untouched. Gardeners can also selectively remove individual leaves that have turned completely brown or become damaged during the summer.
Focus on individual blades that can be pulled or snipped near the base. Avoid cutting into the main, green clump of foliage, as this detracts from the plant’s natural form and does not encourage new growth. Light maintenance during summer supports the plant’s clean appearance, allowing the focus to remain on the lush green foliage and the impressive new plumes that emerge in the late season.