Flooding is detrimental to most terrestrial perennial forage species, often impacting shoot growth and survival. Three sets of plants, legumes, grasses, and alfalfa lines with altered levels of phytoglobin, were treated with either flooding or non-flooding for 10 and 21 days or 14 and 28 days and then allowed to recover for two weeks. Various shoot and root measurements were taken to determine flooding tolerance. Most species tested were negatively impacted by flooding, but two grasses, timothy and reed canarygrass developed positive growth effects. Of the legumes, birds-foot trefoil was highly tolerant of flooding while alfalfa was the most intolerant. Plants with less root damage had greater tolerance, and the presence of aerenchyma led to better root growth. Increased levels of phytoglobin seemed to impart some advantage, but the period of improvement differed between lines. Overall, species flooding tolerance differed with aerenchyma, other root characteristics, and high levels of phytoglobin improved growth and survival.