National flowers & emblems

[badjez]

From before 1900 all ranks in Irish Regiments, together with Irishmen serving in other regiments, were authorised to wear a sprig of shamrock in their headdress on St. Patrick’s Day.
National flowers and emblems have since been extended:
St. George’s Day (Rose) by English units
St. Andrew’s Day (Thistle) by Scottish units
St. David’s Day (Leek) by Welsh units
All units are permitted to wear a Poppy upon Remembrance Sunday.

Can anyone please let me know when each of these ornamentations wre first authorised?

Many thanks, Stephen.