Repotting guide

When & how to repot Giant Arrowhead (Sagittaria montevidensis)

Also called Giant Arrowhead, Aztec Arrowhead, California Arrowhead, Giant Duck Potato.

More about giant arrowhead

About Giant Arrowhead

Sagittaria montevidensis · also called Giant Arrowhead, Aztec Arrowhead · flowering

Sagittaria montevidensis is a robust emergent aquatic perennial native to South America (Uruguay, Argentina, southern Brazil) and naturalised in parts of the southern United States and California. It produces very large, arrow-shaped leaves and impressive white three-petalled flowers with dark maroon basal spots on tall racemes throughout summer and into autumn. As the tallest and most dramatic Sagittaria species in cultivation, its most important care requirement is adequate depth — plant in water 10–15 cm (4–6 in) deep with full sun for maximum size and flower production. Sagittaria species are considered non-toxic to cats and dogs.

Mature size: Foliage 90–120 cm (36–48 in) tall; flower spikes to 150 cm (60 in); clump spread 45–60 cm (18–24 in) in a season.

How to tell giant arrowhead needs repotting

Repotting on a calendar is less reliable than reading the plant. For giant arrowhead, 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 giant arrowhead) 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 giant arrowhead

Only every 2–4 years, when genuinely crowded. Giant Arrowhead 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. Tall, clump-forming emergent aquatic perennial with upright stems bearing very large sagittate leaves and whorled flowers on a stout raceme that can exceed 1 m (3 ft) in height..

What size pot to step giant arrowhead up to

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

Early spring, just as new growth restarts, is the ideal window for giant arrowhead. 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 giant arrowhead

Confirm it actually needs it. Slide giant arrowhead 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 giant arrowhead 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 heavy loam or enriched aquatic compost, 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 giant arrowhead 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 giant arrowhead

Giant Arrowhead wants heavy loam or enriched aquatic compost. Use a dense loam-based mix rather than peat compost to anchor the large root system; top-dress with pea gravel to prevent soil dispersal into the pond water. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting giant arrowhead — frequently asked questions

How often should you repot giant arrowhead?

Only every 2–4 years, when genuinely crowded for giant arrowhead. Only repot giant arrowhead 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 heavy loam or enriched aquatic compost. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does giant arrowhead need?

When is the best time of year to repot giant arrowhead?

Does giant arrowhead like to be root-bound?

Yes — giant arrowhead 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 giant arrowhead after repotting?

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