1 litre sized pot.  Persicaria amplexicaulis Firetail is a clump forming hardy perennial with large pointed green leaves.  It blooms over a long season with red flower spikes held up on strong sturdy stems reaching 80 - 120 cm tall.  Likes full sun or can cope with partial shade.  I have it growing alongside tall asters, rudbeckia and heleniums for a great summer/autumn display.