Ornamental grasses require little maintenance, but they eventually need rejuvenation. If your ornamental grass has a large dead space in the center or the grass has been flopping for the last few years, it is probably time to divide it. You may also want to reevaluate the site your plant is growing in. If the flower plumes (called inflorescences) are sporadic or nonexistent, the plant probably does not receive enough light and, in addition to being divided, could benefit from being moved altogether.
Cut back last year's foliage before dividing. For small grasses, such as blue fescue (Festuca), use garden scissors or pruners to cut the grass back to a few inches. With larger grasses, tie rope around them to hold them in place. Large varieties, especially Miscanthus varieties, require stronger pruning tools, from hedge clippers to a weed trimmer or even a chainsaw. Cut larger varieties back to 6 to 8 inches.
Lift smaller grasses with a trowel or shovel, digging sufficiently under the clump so that you do not damage its roots. Larger grasses usually require more muscle. Well-established grasses may require, as the Proven Winners website attests, "a strong back, or three," to lift plants out of the ground. Dig down under roots. Use a crowbar, if necessary, to get the clump out of the ground.
After the clump is lifted, divide it into sections with a good chunk of roots in each. Use a sharp knife for smaller grasses. Larger grasses may be divided with a shovel or with the spade fork method, a dividing technique Tracy DiSabato-Aust describes in her book "The Well-Tended Perennial Garden" (Timber Press; 1998): Hold two spade forks back to back with the forks interlocked. With a single motion, move the handles in opposite directions and split the clump apart. If more muscle is needed, Proven Winners suggests an axe, a concrete saw or even a chainsaw as a last resort.
Take out any dead sections from the divisions. For smaller grasses, further division can often be made by gently loosening the roots, as long as there is enough of a root system for each planting.
Dig holes for divisions in chosen areas. Put planting mix into the holes, along with existing soil. Water the soil, and then plant your divisions to the depth they were in the original clump. Backfill the hole, tamping down lightly as you fill. Water the plant.
Things You Will Need
- Garden scissors or pruners (small grasses)
- Rope (optional)
- Hedge clippers, weed trimmer or chainsaw (large grasses)
- Trowel or shovel (small clumps)
- Crowbar (large clumps)
- Sharp knife or spade forks (small grasses)
- Axe or concrete saw (large grasses)
- Planting mix with organic matter
- According to the Broadview Gardens website, ornamental grasses should be cut back every year and into a mound shape, with the center of the clump cut higher, to help keep the plant from developing the dead space in the center.
- Proven Winners suggests cutting back cool season grasses like feather reed grass (Calamagrostis) in early spring. Warm season grasses such as fountain grass (Pennisetum) and miscanthus should be cut midspring or as new growth is coming in.
- For division, Proven Winners categorizes their guidelines for grasses into cool and warm season. Cool season grasses should be divided in spring; divide warm season ones while they are growing.
- Keep an eye on your divisions for the first few years in terms of water. Once established, ornamental grasses are rather drought tolerant.
- Lightly feed grasses each spring with a garden fertilizer that doesn't have too much nitrogen. Do not overfertilize ornamental grasses, as they tend to weaken with too much nitrogen. Established plants rarely need much fertilizing.
- When cutting grasses, wear gloves and long sleeves and pants, as the leaves can cut the skin like paper does and miscanthus can cause a mild skin irritation for people with sensitive skin.
- Follow manufacturer's directions on any tools, power or manual, used for pruning and dividing, and consider safety at all times.
- Plant ornamental grasses where they will get good air circulation to prevent disease.