Repotting guide

When & how to repot Blue Hair Grass (Koeleria glauca)

Also called Blue hair grass, Glaucous hair grass, Large blue hair grass.

More about blue hair grass

About Blue Hair Grass

Koeleria glauca · also called Blue hair grass, Glaucous hair grass · flowering

Koeleria glauca is a cool-season, clump-forming bunchgrass native to dry sandy and limestone grasslands of central Europe and central Asia, prized for its intensely blue-grey, fine-textured foliage and attractive silvery-green flower spikes in early summer. It is exceptionally tolerant of poor, alkaline, and sandy soils, and thrives in hot, dry conditions where richer soils would cause it to die out. The most important care fact is that it requires very sharp drainage and dislikes clay or fertile soils where it becomes short-lived. Not listed as toxic; considered pet-safe.

Mature size: 25–40 cm tall (10–16 in) in leaf, up to 50 cm (20 in) in flower, spreading to 30–40 cm (12–16 in) wide.

How to tell blue hair grass needs repotting

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

Roots growing out of the drainage holes, or the rootball lifting the plant proud of the rim.
Soil that has shrunk away from the pot sides and no longer holds water.
The pot is unstable because the plant has grown top-heavy.
Old, compacted, broken-down mix that stays wet too long — for a succulent that is a rot risk, so refresh it even if the pot size is fine.

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 blue hair grass

Every 2–3 years, into bone-dry mix. Blue Hair Grass's growth habit — cool-season, semi-evergreen, densely tufted bunchgrass with erect to slightly arching narrow blue-grey leaves. — sets the pace. Koeleria glauca is a cool-season, clump-forming bunchgrass native to dry sandy and limestone grasslands of central Europe and central Asia, prized for its intensely blue-grey, fine-textured foliage and attractive silvery-green flower spikes in early summer. It is exceptionally tolerant of poor, alkaline, and sandy soils, and thrives in hot, dry conditions where richer soils would cause it to die out. The most important care fact is that it requires very sharp drainage and dislikes clay or fertile soils where it becomes short-lived. Not listed as toxic; considered pet-safe.

What size pot to step blue hair grass up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Blue Hair Grass stores water and rots in a large pot of slow-drying soil. A tight terracotta pot that dries fast is far safer than a generous plastic one. Never up-pot a succulent by several sizes.

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 blue hair grass

Spring or summer, while blue hair grass is in active growth and warm, is best — roots recover fastest then, and the plant is not sitting in cool damp soil. Avoid repotting a succulent in winter dormancy.

Step-by-step: repotting blue hair grass

Repot dry. Do not water blue hair grass for several days first. Working with dry roots and dry mix dramatically lowers the rot risk for a succulent.
Pick a snug, fast-draining pot. Choose terracotta one size up at most, with a drainage hole. Have gritty very well-drained, poor, sandy or chalky, alkaline to neutral ready.
Tip it out and clean the roots. Slide the plant out, crumble off the old soil, and trim any black, mushy or dead roots with clean snips.
Pot into dry mix. Set blue hair grass at its original depth in dry gritty mix, firming gently. Do not bury the stem deeper than it was.
Wait a week before watering. Leave it completely dry and out of harsh sun for about 7 days so any damaged roots callus. Only then water lightly.

Aftercare

Keep blue hair grass completely dry and out of fierce sun for about a week so any nicked roots callus before they meet moisture; watering a freshly repotted succulent is the classic way to rot it. Then resume the normal lean, dry rhythm. Do not fertilise for about 3 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for blue hair grass

Blue Hair Grass wants very well-drained, poor, sandy or chalky, alkaline to neutral. Native to sandy heathland and chalk grassland; adding compost or growing in rich, moist soil shortens its lifespan significantly — infertile, gritty soil is genuinely preferable. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting blue hair grass — frequently asked questions

How often should you repot blue hair grass?

Every 2–3 years, into bone-dry mix for blue hair grass. Repot blue hair grass every 2–3 years into a snug pot of very well-drained, poor, sandy or chalky, alkaline to neutral, ideally in spring or summer. Let it sit in dry soil and do not water for about a week afterwards so any nicked roots can callus. Over-potting and watering straight away is what rots succulents.

What size pot does blue hair grass need?

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

Should you water blue hair grass after repotting?

No — not straight away. Repot blue hair grass into dry mix and wait about a week before the first watering so any damaged roots callus over. Watering a freshly repotted succulent is the single most common way to rot one.

Should you fertilise blue hair grass after repotting?

Not immediately. Wait about 3 weeks after repotting blue 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.