Cortaderia or 'Pampas Grass' should be pruned or burnt in Spring.
Burning sounds harmful but is actually the best way to remove the
previous years leaves and plumbs and the ash will fertilise the roots
and encourage strong new growth. If it is planted as part of a mixed
border or next to a fence, pruning is the safer option but make sure
you wear protective gloves as the leaf edges are very sharp.

April is the best time to divide and replant.

Garden Oasis
www.gardenoasis.co.uk