Pruning Ornamental Grasses: How to Groom and Control

fountain grass

Justus de Cuveland / Getty Images

Project Overview
  • Working Time: 1 - 2 hrs
  • Total Time: 1 - 2 hrs
  • Skill Level: Beginner
  • Estimated Cost: $0

Ornamental grasses are fairly new to the landscape scene—they've increased in popularity in the past couple of decades. In regions experiencing drought, native and ornamental grasses are a smart and show-stopping part of the landscape.

Most ornamental grasses are easy to grow, requiring little water and fertilizer and no pesticides. They look equally beautiful planted poolside, blowing in the breeze, in containers on patios, and as accent plants in other areas of the landscape. Yet as more grasses are introduced from other parts of the world that share similar climates, landscape professionals aren't always in agreement on how to handle these exotic imports.

Unlike rose bushes or boxwood hedges, there's not really a tried-and-true method for pruning or grooming ornamental grasses. Not every landscaping pro knows how to take care of everything in the garden, including grasses that can grow quite large.

When to Prune Ornamental Grasses

Still, if you don't cut or groom ornamental grasses in the fall, they can become shaggy messes by spring. Rainy winters make everything in the garden grow, and ornamental grasses are no exception. Your work is cut out for you when the temperatures get warmer if you haven't trimmed back your grasses in the cooler weather.

Pennisetum Setaceum: A Grass for All Seasons

Pennisetum setaceum 'Rubrum', commonly known as fountain grass or purple fountain grass, has been increasingly popular as both an accent plant and focal point in many landscape designs. Although Pennisetum setaceum's growing seasons are summer and fall, in some parts of the western United States where temperatures remain above 20 degrees Fahrenheit, it can bloom and be a mainstay in the garden throughout the winter. In mild climates, moderate, frost-free temperatures allow fountain grass to grow throughout the year.

Some care instructions advise cutting grasses down to a few inches above the ground in fall or spring and dividing clumps when the grass' growth begins to weaken.

While the following instructions were carried out on fountain grass, they are applicable to other types as well. Here's how to get your grasses looking great.

What You'll Need

Equipment / Tools

  • Hand pruners
  • Hedge shears (electric or handheld)
  • Bow saw
  • Gardening gloves
  • Long sleeves
  • Sturdy shoes
  • String, rope, or bungee cord

Instructions

  1. See How the Other Grasses Grow

    Check out your neighborhood or cruise nearby areas where similar-looking ornamental grasses grow. Take pictures of specimens that are beautiful and thriving to get a sense of how you might want to shape your own grasses.

    Parks, botanical gardens, and public places like hotels or nice restaurants often use gardeners and landscapers who treat pruning as an art form, and really know how to cut and groom sedges and flaxes. Observe up close, if possible, and take notes.

  2. Tie up Your Grasses

    Once you're back home, start by gathering your ornamental grass together with your gloved hands and securing it with string, rope, or a bungee. This makes it much easier to cut it all at one time and get it more even. Adjust the rope or cord higher or lower, depending on where you want to cut the grass. Some gardeners prefer to cut the grass below the rope, because the cuttings are easier to dispose of or put in the compost bin.

    You can also grab a bunch of grass in your hand and cut above or below. You'll have to repeat this maneuver several times, but it works and may be easier for quick touch-ups.

    Warning

    Be sure to wear long sleeves or Armadillos—protective sleeves made of heavy-duty canvas over duck canvas—when working with grasses. Some of them have quite sharp edges that can cut your skin if they rub you the wrong way.

    Cutting and grooming ornamental grass makes it healthier. By removing all that dry, old growth that is basically a big mess of dead grass, new growth will actually be exposed to sunlight and fresh air.

    While it might be tempting to mow down a mess like this, removal of the dry stuff and a good shaping is generally all that will be needed. If you are compelled to cut ornamental grass very short, do not trim it any lower than 4 inches from the ground.

  3. Comb Through the Grass

    Tap into your inner hairstylist as you lean over the fountain grass and comb or rake your gloved fingers through the middle of the clump, grabbing all loose and dead or dried-up hairs (blades/branches).

    Comb through the entire mass of grass, and shake it occasionally to get out more dried plant material. You may end up with a good-sized pile of dead stuff, which you should pitch into a portable container as you go along. Otherwise, it's a real chore to clean up all of those blades and clumps of grass after you've done the pruning and grooming.

  4. Keep Things Neat With Quick Trims

    For impromptu touch-ups, grab a bunch of grass blades in one hand, pull them out to the side, and cut with a pair of hand pruners. Repeat throughout. Gather dead or dry-looking canes in your hand and cut down toward the base. To thin out the grass, grab small sections in the middle and cut toward the base, at different heights. Try to leave some height in the middle, then gradually shape a bit lower on the sides. 

    Once it starts blooming, the grass will have a more natural, rounded shape with arching, fountain-like "blades". Hence, the name, fountain grass.

  5. Divide Clumps

    After a few years, ornamental grasses will need to be divided at their base. How can you tell when the time is right? The grass clump will be overgrown, possibly encroaching on neighboring plants or creeping out beyond the border or edge. In some cases, the centers of the grass clumps will have died out and need to be removed.

    Dividing some grasses, like the Mexican feather grass (Nassella tenuissima), is simple—just use a trowel to dig up a portion of the grass, roots and all. You can then divide the clump again, and replant.

    For larger clumps that might have deeper roots, use a spade and some muscle to divide. Depending on the type of grass, you can either trim to a height of about 4 inches and replant, or you can put the entire clump in your composting bin.

Fun Fact

The Facebook group Crimes Against Horticulture offers eyewitness reports of bad plant haircuts, so you certainly don't want to make their list! While a hard, ground-level cut works well with some species, others just need regular light pruning and shaping. Fortunately, ornamental grasses are pretty forgiving even if your pruning skills aren't up to par.

fountain grass
Crimes Against Horticulture
fountain grass
Justus de Cuveland / Getty Images
grass cutting tools
L. H. Taylor
tie grass with bungee
L. H. Taylor
grooming ornamental grasses
L. H. Taylor
cutting ornamental grasses
L. H. Taylor
grooming ornamental grasses
L. H. Taylor

Healthy and Thriving Grasses

Groomed and pruned carefully and not chopped down to obscurity, these ornamental grasses are beautifully formed. Nice, healthy and how it's supposed to look— ornamental.

native grasses
A cluster of native grasses near the front path. Billy Goodnick