Repotting guide

When & how to repot Porcupine Grass (Miscanthus sinensis 'Strictus')

Also called Porcupine grass, Banded miscanthus, Striped eulalia.

More about porcupine grass

About Porcupine Grass

Miscanthus sinensis 'Strictus' · also called Porcupine grass, Banded miscanthus · flowering

Miscanthus sinensis 'Strictus' is a bold, stiffly upright ornamental grass cultivar of the Chinese silver grass species, prized for its distinctive horizontal yellow-cream banding across the arching green leaf blades — a feature unique among upright miscanthus forms. In mid to late autumn it produces airy, pinkish-copper plume panicles that age to silvery-white and persist attractively through winter. The critical care point is full sun — without sufficient light, the characteristic yellow banding fades to plain green. It holds the RHS Award of Garden Merit. Miscanthus grasses are not listed as toxic by the ASPCA, but classified as mildly-toxic due to the potential for mechanical injury from sharp leaf edges and limited specific pet-safety data.

Mature size: 150–200 cm tall (to 250 cm with flower plumes), spreading 90–120 cm wide.

How to tell porcupine grass needs repotting

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

Roots spiralling thickly out of the drainage holes or pushing the whole plant up out of the pot.
The pot is so packed that water runs straight through in seconds and barely wets the soil.
It has split a plastic pot, or the rootball is a solid mass with almost no soil left when you slide it out.
Growth and (for porcupine grass) flowering have clearly stalled despite good light and feeding — but remember this plant likes being snug, so a little crowding alone is not a reason to repot.

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 porcupine grass

Only every 2–4 years, when genuinely crowded. Porcupine Grass is one of the plants that genuinely prefers a snug pot — it grows and flowers better with its roots a little restricted, so resist the urge to repot it on schedule. Stiffly upright, clump-forming deciduous ornamental grass with strongly vertical, arching foliage..

What size pot to step porcupine grass up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Porcupine Grass positively prefers a snug pot: it flowers and grows better when the roots are a little restricted. The single biggest repotting mistake here is over-potting — dropping porcupine grass into a pot two or three sizes up. All that surplus soil holds water the small root system cannot use, stays cold and wet, and rots the roots within weeks. When in doubt, choose the smaller pot.

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 porcupine grass

Early spring, just as new growth restarts, is the ideal window for porcupine 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 porcupine grass

Confirm it actually needs it. Slide porcupine grass out and check the roots. Only continue if it is genuinely packed — this plant prefers a snug pot, so if there is still soil and room, put it straight back.
Pick a pot only one size up. Choose a pot just 2–3 cm wider with good drainage. Resist anything bigger; over-potting is the main killer here.
Ease it out gently. Water lightly the day before, then tip porcupine grass out, supporting the base. Tease the outer roots free only enough to stop them circling.
Repot at the same depth. Add a layer of fresh moderately fertile, moist but well-drained loam; tolerates clay and sandy soils (ph 5.5–7.5)., set the plant so the soil line sits exactly where it did before, and backfill around the sides, firming lightly.
Settle it in. Water once to settle the soil, then let it sit. Hold off on more water until the top of the soil dries — fresh soil around a small root system stays wet for a while.

Aftercare

Because the new soil holds more water than the old crammed rootball did, ease right back on watering — let the top of the soil dry before you water porcupine grass again, or you will rot the roots in the very pot you just moved it to. Keep it out of harsh direct sun for a fortnight. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for porcupine grass

Porcupine Grass wants moderately fertile, moist but well-drained loam; tolerates clay and sandy soils (ph 5.5–7.5).. Adaptable to a range of soil types including clay and sandy soils. Avoid excessively wet or poorly drained positions, particularly in winter, to prevent crown rot. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting porcupine grass — frequently asked questions

How often should you repot porcupine grass?

Only every 2–4 years, when genuinely crowded for porcupine grass. Only repot porcupine grass every 2–4 years, and only when it is genuinely root-bound — it flowers and grows best slightly crowded. Step up just one pot size in spring using moderately fertile, moist but well-drained loam; tolerates clay and sandy soils (ph 5.5–7.5).. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does porcupine grass need?

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

Does porcupine grass like to be root-bound?

Yes — porcupine grass genuinely flowers and grows best when slightly pot-bound, so do not rush to repot it. The mistake to avoid is over-potting into a much larger pot: the excess soil stays wet, the roots cannot use it, and the plant rots. Only repot every few years and only one snug size up.

Should you fertilise porcupine grass after repotting?

Not immediately. Wait about 4 weeks after repotting porcupine 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.