Why divide ornamental grasses
Dividing a clump-forming grass does a few useful things: it makes new plants for free, reduces a clump that has outgrown its spot, and renews an older plant. Many grasses tend to die out in the center as they age, leaving a ring of growth around an empty or woody middle. Dividing fixes that.
Yes, you can split decorative grasses, and most clumping types handle it well. The same technique is used for moving a plant to a new place.
Signs a clump needs dividing
- A bare or dead patch in the middle, a common problem with blue fescue.
- Fewer and weaker flower plumes than before.
- The clump has outgrown its space or is flopping outward. See why grasses flop over.
- You simply want more plants.
As a rule of thumb, different sources suggest every two to five years, depending on the species and how fertile the soil is. Some, such as Miscanthus, are often said to need dividing every three or four years. Others, like switchgrass, may go much longer.
Best time to divide and move
The general principle from Proven Winners and other nurseries is to divide when the plant is actively growing, but not while it is flowering. If a plant is dormant when moved, it tends to root poorly.
- Cool-season grasses: spring or early fall. Early spring is often considered best.
- Warm-season grasses: spring through midsummer, once growth has started. Early to mid spring is the most forgiving.
- Evergreen grasses and sedges: spring only, since division wounds the plant and they never fully go dormant.
Can you split grasses in the fall?
Yes, for cool-season types, in early fall, if there is enough time left to root. Take care that freeze and thaw cycles do not push small divisions out of the ground. Warm-season grasses are better left until spring.
Is it too late to transplant?
If a grass is dormant and the ground is frozen or about to freeze, it is probably too late to move it this year. Wait until growth begins in spring. Avoid moving plants during hot, dry spells in summer.
What you need
- A sharp spade or garden fork
- A sharp knife, or a hand saw for tough clumps
- Gloves and long sleeves, since leaves can be sharp
- A tarp to lay the clump on
- Compost, mulch and a hose
How to divide step by step
- Cut the plant back. Trim the foliage to a few inches first, so you can see what you are doing. See cutting back ornamental grasses.
- Water the day before. Moist soil holds the root ball together.
- Dig around the clump. Cut a circle wide enough to take most of the roots and lift the clump out.
- Split it. Use a spade, a knife or a saw to cut the clump into sections. Each piece needs healthy roots and some shoots. Discard any dead or woody center.
- Replant quickly. Set each piece at the same depth it was growing before, firm the soil and water thoroughly. Do not let exposed roots dry out.
- Keep spare pieces moist. If you cannot plant right away, pot them up or cover roots with damp material and keep them in shade.
Dividing very large clumps
Big, old grasses can be hard work. Proven Winners suggests digging or prying the clump out, then cutting it into pieces with a very sharp shovel, a saw or an axe. A chain saw works but is rough on the plant and is a last resort. Another approach is to cut a few pieces off the outer edge of a healthy clump without lifting the whole plant. An alternative is to cut the grass to the ground, then wedge the clump into sections before lifting them out.
Moving a whole grass
For transplanting without splitting, use the same timing. Cut the plant back, dig a root ball as large as you can manage, move it with a tarp, and replant at the same depth in prepared soil. Water well until established. You can also check how to plant ornamental grasses for the finer points on depth and mulch.
Aftercare
Newly divided pieces need frequent watering while roots develop. Once they are well rooted you can reduce watering. You do not normally need fertilizer, as explained in whether to fertilize ornamental grasses.
Frequently asked questions
Can you grow ornamental grass from seed?
Often yes for species, but it is slower; see where to find ornamental grass seeds for sale. Many named cultivars do not come true from seed, so division is the standard way to propagate them.
Does ornamental grass spread?
Clumping grasses widen slowly. Running grasses spread by rhizomes or stolons, and dividing them is a good way to keep them in bounds. See the care overview for more on clumping versus spreading.