Repotting guide

When & how to repot Mondo Grass (Ophiopogon japonicus)

Also called mondo grass, monkey grass, dwarf lilyturf.

More about mondo grass

About Mondo Grass

Ophiopogon japonicus · also called mondo grass, monkey grass · houseplant

Ophiopogon japonicus is a tough, grass-like evergreen perennial (a lily relative, not a true grass) forming dense clumps of dark green strappy foliage. It tolerates shade, spreads slowly by stolons, and bears small lilac-white summer flowers followed by blue berries. Widely used as a slow groundcover, edging or low-maintenance container plant indoors and out.

Mature size: Around 15-30 cm tall, spreading slowly and indefinitely by stolons to form broad mats.

Watch for — Yellowing in wet soil: Waterlogged or poorly drained soil yellows leaves and rots roots. Improve drainage and let the surface dry slightly between waterings.

How to tell mondo grass needs repotting

Repotting on a calendar is less reliable than reading the plant. For mondo grass, watch for these signs:

Roots poking out of the drainage holes or coiling visibly around the inside of the pot.
You are watering far more often than you used to because the rootball dries out within a day or two.
Water runs straight through and out the bottom without soaking in.
Top growth has slowed or new mondo grass leaves are noticeably smaller than older ones despite good light.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot mondo grass

Every 12–18 months — sooner if roots show fast. Mondo Grass's growth habit — evergreen, clump- and mat-forming perennial spreading slowly by short underground stolons. produces fountains of fine, arching, dark green leaves; mature colonies knit into a dense, low groundcover. — sets the pace. Ophiopogon japonicus is a tough, grass-like evergreen perennial (a lily relative, not a true grass) forming dense clumps of dark green strappy foliage. It tolerates shade, spreads slowly by stolons, and bears small lilac-white summer flowers followed by blue berries. Widely used as a slow groundcover, edging or low-maintenance container plant indoors and out.

What size pot to step mondo grass up to

Step up one pot size — about 2–3 cm (an inch) wider. Mondo Grass grows fast, so it will fill that space within a season, but jumping several sizes at once still backfires: the unused soil stays soggy and rots even a vigorous root system. One size at a time, every year or so, is the rhythm.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot mondo grass

Early spring, just as new growth restarts, is the ideal window for mondo grass. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting mondo grass

Time it for spring. Repot mondo grass in early spring as growth restarts so it re-roots quickly into the fresh soil.
Choose one size up. Pick a pot about 2–3 cm wider with drainage holes. One step only — a much bigger pot stays soggy and rots roots.
Ease the plant out. Water lightly the day before, then tip mondo grass out and gently loosen any roots circling the bottom of the rootball.
Repot at the same depth. Put a layer of fresh fertile, moisture-retentive, well-drained loam; slightly acidic preferred in the new pot, set the plant so its soil line is unchanged, and backfill, firming lightly.
Water and pause feeding. Water once to settle the soil. Hold off fertiliser for about a month — fresh mix already has nutrients and feeding now burns new roots.

Aftercare

Water mondo grass once to settle the soil, then let the surface dry before watering again — fresh mix around the roots stays wetter than the old compacted ball, so the commonest post-repot mistake is overwatering. Keep it out of direct sun for a week or two while roots re-establish. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for mondo grass

Mondo Grass wants fertile, moisture-retentive, well-drained loam; slightly acidic preferred. Humus-rich, free-draining soil suits it best. In pots use a quality, moisture-retentive potting mix with added grit; it adapts to most soils but resents heavy waterlogging. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting mondo grass — frequently asked questions

How often should you repot mondo grass?

Every 12–18 months — sooner if roots show fast for mondo grass. Repot mondo grass roughly every 12–18 months, in early spring as growth restarts. It grows fast and circles its pot quickly, so step up one size (about 2–3 cm wider) into fresh fertile, moisture-retentive, well-drained loam; slightly acidic preferred. Don't jump several sizes — that soggy excess soil is what rots vigorous roots.

What size pot does mondo grass need?

When is the best time of year to repot mondo grass?

Can you put mondo grass straight into a much bigger pot?

No. Even a fast-growing mondo grass should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.

Should you fertilise mondo grass after repotting?

Not immediately. Wait about 4 weeks after repotting mondo grass. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.