To extend the bloom period for wildflower gardens, sow seeds over a longer period of time, from October through February to extend the exuberance of the wildflower season into late spring and summer. You might even reseed in March and April.
Include late blooming annuals in the mix. The pretty pinks of clarkias (Clarkia amoena, C. unguiculata) will adorn your garden in May and June. Madias (Madia elegans), tarweeds (Hemizonia spp.) and sunflowers (Helianthus annuus) provide cheerful yellow flowers into the summer. Cut back poppies (Eschscholzia californica) after their first bloom period and they will return for a second, and possibly third bloom, brightening your summer garden with their brash orange flowers.
As the season progresses selectively remove and cut back the wildflowers, leaving some seed for the birds. If you do not water your wildflower beds during the summer, they will reseed themselves. If the garden receives summer water, collect the seed and sow it next fall and winter.