Aims Inter-specific comparisons of plant traits may vary depending on intra-specific variation. Here we examine the impact of root branching order and season on key functional root traits for grass species.We also compare root traits among co-existing grass species as a step towards defining root trait syndromes. Methods Monocultures of 13 grass species, grown under field conditions and subjected to intensive management, were used to record root trait values for coarse roots (1st order, >0.3 mm), fine roots (2nd and 3rd orders, <0.2 mm) and mixed root samples over three growing seasons. Results Branching order and species had a significant effect on root trait values, whereas season showed a marginal effect. The diameter of coarse roots was more variable than that of fine roots and, as expected, coarse roots had higher tissue density and lower specific root length values than fine roots. Principal component analysis run on eight root traits provided evidence for two trait syndromes related to resource acquisition and conservation strategies across grass species. Conclusions Our data show that root branching order is the main determinant of root trait variation among species. This highlights the necessity to include the proportion of fine vs coarse roots when measuring traits of mixed root samples.