Summary:Echium plantagmeum is a widespread, persistent, and often dominant votunteer species in southern Australia. In pastures. it commonly grows with Trifolium subterraneion. This paper describes glasshouse studies investigating the effects of soil fertility. plant density. sward composition, defoliation frequency. and delayed estabilishment of t. subserraneum on the growth of E. pluntagineum and T. subterraneum when grown in pure swards and in mixtures.Generally. herbage production of swards was increased by the presence of E. plantagineum. the addition of nutrogen and phosphorus fertilizers, and increasing density, It was decreased by defoliation. E. pluntagineum plants generally produced more shoots and roots than did T. subterraneum. Both species responded. E. plantiagineum generally more than T. subterraneum. to added phosphorus and nitrogen fertilizers. Both species showed a non‐linear reduction in plant size as plant density of the sward was increased. especially during early growth. E. plantagineum was, however. more plastic in its response to density than T. subterraneum. Defoliation reduced the plant weight of both species. more for E. plantagineum than for T. subterraneum.In mixtures. there was little competition between the two species during early growth. when swards were defoliated and when both species established at the same time. T. subserraneum was, howerver. sometimes suppressed during later growth if swards were undefoliated. if soil fertility was high. and if E. plantaginteum established before t. subserraneum. Such competition appeared to be between shoots rather than between roots.In the field. E. plantagineum is likely to be fovoured in undergrazed situations, where soil fertility is high and when false or early seasonal breaks allow it to establish earlier than t. subterruneum. Its high productivity under a wide range of pasture situations ‐ especially in autumn and winter when pasture availability is ofter critically low and the fact that it is relatively nutritious and readily eated by stock suggest that it is a useful pasture spec