How far along to harvest viable allium seeds?

rouge21_gw (CDN Z6a)
5 months ago
last modified: 5 months ago

The alliums in question have dead foliage and the flower heads are now only green seeds. If I remove the head at this point will these seeds be usable for this Fall or next spring or do I need to leave the allium head alone ie on its stalk in the ground until the seeds turn brown?