Tetraploid plants, including those induced from diploid barrel medic (Medicago truncatula Gaertn.) and the snail medic [Medicago scutellata (L.) Mill.], have the potential to increase vigor and leaf size to improve adaptation to environments with low and variable rainfall in Mediterranean climates. The growth of tetraploid lines induced from barrel medic cultivar Sultan‐SU was evaluated against the diploid parent line and a natural tetraploid snail medic cultivar Sava in field conditions in Adelaide, South Australia. In field conditions, tetraploid lines had up to 106% greater autumn biomass than Sultan‐SU, 58% larger seed weight, and a 127% increase in leaf area. In a controlled environment experiment, snail medic Sava was the only entry to show improved early season (assessed at 6 wk) shoot biomass and canopy cover under short days and low temperatures that were designed to simulate a late start to the growing season. An examination of fresh flower buds showed that the fertility and stability of induced tetraploid lines varied between lines and generations. Hardseed breakdown patterns differed among tetraploid mutant lines, with two lines having much harder seed than Sultan‐SU. Some tetraploid Medicago spp. produced greater early biomass and larger leaves than diploids. Increasing ploidy level provides plant breeders with a promising tool in the development of new cultivars better suited to future climate scenarios.