The short answer
For most gardens, the simplest rule is to leave ornamental grasses standing through winter and cut deciduous types back in late winter or early spring, just before new growth starts. Fall cutting is perfectly workable, and is sometimes the better choice, but spring is the default most gardeners and horticultural sources recommend. For a quick answer by type, see should all ornamental grasses be cut back in the spring?
Know which type you have
The right approach depends on the group your grass belongs to (the groups are explained in warm-season vs cool-season ornamental grasses).
- Warm-season grasses (Miscanthus, switchgrass, fountain grass, northern sea oats) turn brown after frost. They are typically cut low, to a few inches above the ground.
- Cool-season grasses (feather reed grass, blue oat grass, tufted hair grass) start growing early. Several sources advise cutting them back in very early spring and not too hard, leaving about a third of the plant, because harsh cutting can harm them.
- Evergreen grasses and grass-like plants (many sedges, some fescues, mondo grass) are usually not cut down. Instead, you comb out or pull out the dead leaves by hand and snip off damaged tips. The RHS suggests that some evergreen grasses do not always respond well to hard pruning. See evergreen ornamental grasses that stay green all year for which plants fall in this group.
Not sure which you have? Check the plant label, or see the overview in our ornamental grass care guide.
Cutting back in spring
Spring cutting has several advantages. The standing foliage and seed heads give winter interest, insulate the crown and shelter birds and beneficial insects, and the old growth traps snow. You then remove it before the new shoots come up through it.
Timing varies by plant and climate. Sources commonly give a window from late winter to mid spring, depending on how early your grass wakes up. Miscanthus and some fountain grasses are slower to start, so they can be cut a little later without harm, but the goal is to finish before new green growth is well under way.
When fall trimming makes sense
You may prefer, or need, to cut in fall in a few situations.
- Fire risk. In wildfire-prone regions, dry standing grass near buildings is a hazard. Local guidance may recommend removing it at the end of the season, and may discourage planting highly flammable plants close to the house. Follow your local fire authority’s advice.
- Appearance. Some grasses look untidy or collapse in winter, and some gardeners dislike the mess near paths or entrances.
- Spread by seed. If a grass self-seeds where you do not want it, cutting off seed heads before they ripen helps. Some sources recommend this for fountain grass and Miscanthus in regions where they seed freely.
- Warm-season grasses once dormant. Once these turn brown, they can be trimmed more or less any time, according to Proven Winners.
The downside of cutting early is that the exposed crowns lose their natural insulation and open stalks can collect water. In very cold areas, leaving a little extra height, several inches, may help protect the crown. If you cut in fall, our article on what to do with ornamental grass in the fall covers the rest of the autumn to-do list.
How far down to cut
Typical guidance for deciduous clump-forming grasses is to cut to about 3 to 6 inches above the ground. The RHS recommends cutting as low as possible without damaging new shoots for deciduous grasses in the UK, while many North American sources leave a few inches. Very large grasses with thick stems, such as big Miscanthus, may need to be cut a bit higher, since the base is tough. If your grass is a cool-season type, leave more foliage than for a warm-season grass.
How to cut back, step by step
- Wear protection. Thick gloves, long sleeves and eye protection. Grass blades can have sharp edges.
- Bundle the clump. Wrap twine, a bungee cord or wide tape around the stalks, in a couple of places on a tall plant. This keeps the cuttings together and makes cleanup far easier.
- Cut across the bundle. Hand pruners, sharp hedge shears or a pruning saw work for most clumps. A hedge trimmer helps on large, dense plants. Keep the blades sharp.
- Clear the debris. Lift the bundle away, rake up loose bits and compost the cuttings. If you want them to rot faster, chop them smaller first.
- Tidy the bed. Weed and, if you like, add a light mulch.
What if new growth has started
If you are late and new shoots are already showing, one suggested approach is to avoid cutting the new growth. Either cut only the old tops higher up, or work carefully around the new shoots. Cutting through green shoots leaves blunt, brown tips for the season.
What happens if you don’t cut back
Nothing dramatic. The plant will just look untidier, old foliage will build up, and new growth will have to push up through the dead stalks. Over time, a clump can also become congested in the center. If you notice this, the fix is usually dividing rather than more trimming; see dividing and transplanting ornamental grasses.
Can you burn ornamental grass?
Burning is a traditional way to clear prairie plantings, but it is not recommended in home gardens. It is often prohibited or restricted by local rules, it is a fire hazard, and the RHS specifically advises against burning pampas grass because the crown can be damaged. Cutting is safer.
Frequently asked questions
Does ornamental grass need to be trimmed?
Most deciduous clumping grasses benefit from an annual cutback. Evergreen types need only a tidy.
Does mondo grass follow the same rules?
Not exactly. See when to cut back mondo grass for its own timing.