Wildflowers may begin blooming in the lower elevations of the Pinto Basin and along the park's south boundary in February and at higher elevations in March and April. Desert regions above 5,000 feet may have plants blooming as late as June. The extent and timing of spring wildflower blooms in Joshua Tree vary from one year to the next. Fall and winter precipitation and spring temperatures are key environmental factors affecting the spring blooming period. Normally, desert annuals germinate between September and December. Many need a good soaking rain to get started. In addition to rains at the right time, plants also require temperatures to warm a bit before flower stalks will grow. Green-leaf rosettes may cover the ground in January, but flower stalks wait until temperatures rise.