Repotting guide

When & how to repot Reed Sweet-grass (Glyceria maxima)

Also called Reed Sweet-grass, Reed Mannagrass, Great Sweet-grass.

More about reed sweet-grass

About Reed Sweet-grass

Glyceria maxima · also called Reed Sweet-grass, Reed Mannagrass · flowering

Reed Sweet-grass is a tall, aggressive aquatic grass native to Europe and Asia, forming extensive stands in slow rivers, ditches, and pond margins. Its succulent young shoots are highly palatable to waterfowl and livestock, giving it the 'sweet-grass' name. The variegated cultivar 'Variegata' is popular in ornamental water gardens for its cream-striped foliage.

Mature size: 100–200 cm tall, spreading indefinitely via rhizomes

How to tell reed sweet-grass needs repotting

Repotting on a calendar is less reliable than reading the plant. For reed sweet-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 reed sweet-grass

Every 2–3 years, into bone-dry mix. Reed Sweet-grass's growth habit — strongly rhizomatous, colony-forming aquatic grass — sets the pace. Reed Sweet-grass is a tall, aggressive aquatic grass native to Europe and Asia, forming extensive stands in slow rivers, ditches, and pond margins. Its succulent young shoots are highly palatable to waterfowl and livestock, giving it the 'sweet-grass' name. The variegated cultivar 'Variegata' is popular in ornamental water gardens for its cream-striped foliage.

What size pot to step reed sweet-grass up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Reed Sweet-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 reed sweet-grass

Spring or summer, while reed sweet-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 reed sweet-grass

Repot dry. Do not water reed sweet-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 aquatic compost or fertile loam/clay; tolerate silt 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 reed sweet-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 reed sweet-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 reed sweet-grass

Reed Sweet-grass wants aquatic compost or fertile loam/clay; tolerate silt. Grows in virtually any fertile, waterlogged substrate including natural silt and clay. For pond baskets, use aquatic compost topped with pea gravel. Very adaptable to pond margin and shallow water 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 reed sweet-grass — frequently asked questions

How often should you repot reed sweet-grass?

Every 2–3 years, into bone-dry mix for reed sweet-grass. Repot reed sweet-grass every 2–3 years into a snug pot of aquatic compost or fertile loam/clay; tolerate silt, 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 reed sweet-grass need?

When is the best time of year to repot reed sweet-grass?

Should you water reed sweet-grass after repotting?

No — not straight away. Repot reed sweet-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 reed sweet-grass after repotting?

Not immediately. Wait about 3 weeks after repotting reed sweet-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.