Quick answer: 45 native California plants have a recorded bloom range that includes May.
45 species
- Alderleaf mountain mahogany Cercocarpus montanus · 9 states
- Apache plume Fallugia paradoxa · 6 states
- Banana yucca Yucca baccata · 6 states
- Bearberry Arctostaphylos uva-ursi · 16 states
- Blueblossom Ceanothus thyrsiflorus · 1 states
- California bay laurel Umbellularia californica · 3 states
- California buckwheat Eriogonum fasciculatum · 2 states
- California wild grape Vitis californica · 1 states
- Cardinal flower Lobelia cardinalis · 37 states
- Checker lily Fritillaria affinis · 3 states
- Coast live oak Quercus agrifolia · 1 states
- Common camas Camassia quamash · 3 states
- Common elderberry Sambucus nigra ssp. canadensis · 16 states
- Common selfheal Prunella vulgaris · 2 states
- Common yarrow Achillea millefolium · 31 states
- Coulter's Matilija poppy Romneya coulteri · 1 states
- Creeping Oregon grape Mahonia repens · 11 states
- Creosote bush Larrea tridentata · 5 states
- Desert globemallow Sphaeralcea ambigua · 2 states
- Desert marigold Baileya multiradiata · 4 states
- Desert willow Chilopsis linearis · 4 states
- Douglas iris Iris douglasiana · 3 states
- Eastern redbud Cercis canadensis · 30 states
- Firecracker penstemon Penstemon eatonii · 3 states
- Golden currant Ribes aureum · 3 states
- Honey mesquite Prosopis glandulosa · 3 states
- Hummingbird sage Salvia spathacea · 1 states
- Indigo bush Amorpha fruticosa · 16 states
- Jojoba Simmondsia chinensis · 2 states
- Joshua tree Yucca brevifolia · 3 states
- Pacific madrone Arbutus menziesii · 3 states
- Pacific trillium Trillium ovatum · 3 states
- Palmer's penstemon Penstemon palmeri · 3 states
- Prairie Junegrass Koeleria macrantha · 15 states
- Red-osier dogwood Cornus sericea · 22 states
- Rocky Mountain bee plant Peritoma serrulata · 22 states
- Rocky Mountain iris Iris missouriensis · 7 states
- Silver buffaloberry Shepherdia argentea · 11 states
- Silver lupine Lupinus albifrons · 1 states
- Tall Oregon grape Mahonia aquifolium · 3 states
- Toyon Heteromeles arbutifolia · 1 states
- Valley oak Quercus lobata · 1 states
- Western azalea Rhododendron occidentale · 3 states
- White sage Salvia apiana · 1 states
- Wyoming Indian paintbrush Castilleja linariifolia · 4 states