How to Prune allium 'Ping Pong'?
No pruning required, other than to remove old flowered stems and foliage

allium 'Ping Pong' · Allium 'Ping Pong'
Grow in full sun and a fertile well-drained soil. It is best to grow in containers where garden soil is heavy clay and prone to saturation over winter. See allium cultivation
No pruning required, other than to remove old flowered stems and foliage