Weld (Reseda luteola) also known as Dyers Weld is one of the oldest used natural dyes known and is perfect for natural dyeing which can easily be added and removed from the dye bath - you could also infuse first then use the dye liquor for your natural dyeing.  Whole dyestuff is perfect also for yarn dyeing where you wish to avoid any particles remaining in the batch. 
 
Weld yields an intense yellow colour depending on quantity used, the fibres used, and the pH of your dye bath too (i.e. whether you use any dye modifiers such as acids or alkaline).  With dye modifiers you can achieve many shades of yellow, golden and greeny yellows.  Mordants are necessary so use Alum mordant for when dyeing animal (protein) fibres, and a tannin plus ALUM or Aluminium acetate when dyeing plant (cellulosic) fibres.  You can overdye with indigo or woad to create a fabulous Lincoln green colour.
 
Smallest pack size supplied is 100g
 
Recommended use is at least 40-50% weight of fibre/fabric (WOF) to reach an intense yellow colour