I have grown many varieties of Corydalis in my shade gardens – some I like more than others. Corydalis lutea is probably the most commonly available. It has ferny blue-green or green leaves that are covered by yellow flowers in spring. Flowering will continue into summer (but not as heavily as the spring flush). It is not uncommon for Corydalis to die back (go dormant) in hot summer heat. Many times (not always) it will reappear in fall with cooler temperatures, or the following spring. This charming flower blooms all summer in my Maine garden. It is hardy in Zones 4-8.
Other Corydalis that I have grown include Corydalis ochroleuca (white and yellow flowers, Z4-8), C. flexuosa (blue flowers, Z5-9, pictured is ‘Blue Heron’ in my garden), C. anthriscifolia ‘Blackberry Wine’ and C. sempervirens (pink and yellow flowers, Z2-6). ALL Corydalis can be short-lived, but many reseed prolifically as a result. They DO NOT like being divided. They have fleshy hollow stems and roots. They require well-drained soil in part sun (in coolers zones) to shade. Corydalis partners well with Hosta, Brunnera, Hakone grass (Hakonechloa) and Lady’s Mantle. NOTE: Corydalis is toxic to livestock.