In laboratory studies only 1 out of 20 seeds germinated under conditions used successfully for other Hedeoma species. Todsen's pennyroyal is restricted to 2 small populations in the San Andres Mountains of South-central New Mexico. In total there are approximately 750 plants known from the two sites. These sites cover an estimated combined area of 3,000 square meters. The populations appear to be limited to gravelly loose north facing slopes of a gypseous-limestone substrate.
Nothing is known about their survival or mortality rates.
The S.C.S. Soil Association describes the soil type as a member of the Deama-Rock outcrop complex. It has no soil profile development and is a highly erodible soil. The populations are restricted to more mesic north and northeast facing slopes of approximately 33 percent. The soil is very loose and extremely susceptible to disturbance. Todsen's pennyroyal occurs in the Great Basin Conifer Woodland Biotic Community.