Repotting guide

When & how to repot bluejoint reedgrass (Calamagrostis canadensis)

Also called bluejoint reedgrass, bluejoint, Canadian reedgrass.

More about bluejoint reedgrass

About bluejoint reedgrass

Calamagrostis canadensis · also called bluejoint reedgrass, bluejoint · flowering

Bluejoint reedgrass is a vigorous native North American cool-season grass thriving in wet meadows, marshes, and streambanks. It forms dense stands of upright, arching stems topped with purple-tinged panicles in early summer that fade to tawny gold. Excellent for naturalising wet and boggy areas, it provides important wildlife and waterfowl habitat and erosion control along watercourses.

Mature size: 90-150 cm tall and spreading indefinitely via rhizomes in suitable moist conditions.

Watch for — Aggressive spreading: In moist, fertile conditions bluejoint spreads vigorously by rhizomes and can become invasive in small gardens; site only where spread is acceptable or install root barriers.

How to tell bluejoint reedgrass needs repotting

Repotting on a calendar is less reliable than reading the plant. For bluejoint reedgrass, 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 bluejoint reedgrass) 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 bluejoint reedgrass

Only every 2–4 years, when genuinely crowded. bluejoint reedgrass 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. Strongly rhizomatous, colony-forming cool-season deciduous grass; spreads aggressively by rhizomes in moist soils to form dense stands. Not suited to small formal borders where its spread would need control..

What size pot to step bluejoint reedgrass up to

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

Early spring, just as new growth restarts, is the ideal window for bluejoint reedgrass. 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 bluejoint reedgrass

Confirm it actually needs it. Slide bluejoint reedgrass 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 bluejoint reedgrass 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 wet, poorly drained, or seasonally flooded soils; adaptable to clay, peat, or loam, 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 bluejoint reedgrass 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 bluejoint reedgrass

bluejoint reedgrass wants wet, poorly drained, or seasonally flooded soils; adaptable to clay, peat, or loam. Highly adaptable to wet, heavy soils including waterlogged clay and peat. Naturalises in riparian zones and wet meadows. Not suited to dry, free-draining soils where it struggles and thins out. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting bluejoint reedgrass — frequently asked questions

How often should you repot bluejoint reedgrass?

Only every 2–4 years, when genuinely crowded for bluejoint reedgrass. Only repot bluejoint reedgrass 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 wet, poorly drained, or seasonally flooded soils; adaptable to clay, peat, or loam. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does bluejoint reedgrass need?

When is the best time of year to repot bluejoint reedgrass?

Does bluejoint reedgrass like to be root-bound?

Yes — bluejoint reedgrass 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 bluejoint reedgrass after repotting?

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