Repotting guide

When & how to repot wavy hair grass (Deschampsia flexuosa)

Also called wavy hair grass, crinkled hair grass.

More about wavy hair grass

About wavy hair grass

Deschampsia flexuosa · also called wavy hair grass, crinkled hair grass · flowering

Wavy hair grass is a delicate, wiry cool-season perennial grass of acid heathlands, moorlands, and open woodlands in Europe and North America. Its slender, hair-fine leaves form low, dark-green tussocks from which airy, wavy-stemmed panicles of tiny, glistening spikelets rise in early summer. Ideal for acid soils, heath gardens, and naturalised moorland settings with striking translucent flower clouds.

Mature size: Foliage tufts 15-30 cm tall; flowering stems reach 40-70 cm tall and 30-45 cm wide.

Watch for — Heat and drought stress: Foliage browns and thins in hot, dry summers away from its native cool, moist moorland climate; site in the coolest available spot with some afternoon shade in warm regions.

How to tell wavy hair grass needs repotting

Repotting on a calendar is less reliable than reading the plant. For wavy hair 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 wavy hair 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 wavy hair grass

Only every 2–4 years, when genuinely crowded. wavy hair 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. Dense, tufted, clump-forming cool-season semi-evergreen grass; low, wiry basal mound with tall, slender, wavy flowering stems rising well above the foliage..

What size pot to step wavy hair grass up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. wavy hair 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 wavy hair 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 wavy hair grass

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

Confirm it actually needs it. Slide wavy hair 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 wavy hair 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 acid, free-draining, nutrient-poor sandy or peaty soil, 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 wavy hair 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 wavy hair grass

wavy hair grass wants acid, free-draining, nutrient-poor sandy or peaty soil. Requires acid soil (pH 4.5-6.5); thrives in sandy, peaty, or thin humus soils typical of heathland. Struggles or dies in neutral to alkaline or heavy clay soils. Do not lime and avoid adding rich compost — it prefers lean, poor conditions. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting wavy hair grass — frequently asked questions

How often should you repot wavy hair grass?

Only every 2–4 years, when genuinely crowded for wavy hair grass. Only repot wavy hair 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 acid, free-draining, nutrient-poor sandy or peaty soil. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does wavy hair grass need?

When is the best time of year to repot wavy hair grass?

Does wavy hair grass like to be root-bound?

Yes — wavy hair 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 wavy hair grass after repotting?

Not immediately. Wait about 4 weeks after repotting wavy hair 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.