Serrated tussock ('Nassella trichotoma' (Nees) Arechav.) is a perennial grass weed of pastures. It is a widespread problem on the Southern Tablelands of New South Wales (NSW) that have a Mediterranean climate and is now invading the Northern Tablelands of NSW where rainfall is summer dominant. Isolated infestations are found under trees and in open areas. Due to the importance of wind-borne seeds to the invasive capability of serrated tussock and the suppression of seeding in effective management, it is necessary to understand when plants set seed and the factors that affect the level of seed production. In particular a reduction in the intensity or amount of light received by a plant can have implications on physiological responses such as changes in seed production. The aim of this study was to assess the effect of shade on the timing and amount of seed production.