Cardamine diphylla is a cute wintergreen groundcover with clusters of small, white, four-petaled flowers in spring popular with bees and butterflies.

Caryopteris incana 'Beyond Pink'd' is a deciduous shrub known as bluebeard with masses of pink flowers full of nectar.

Caryopteris x clandonensis ‘Beekeeper’ is a compact bluebeard with blue flowers and golden-green foliage.

Caryopteris Grand Blue produces masses or rich blue flowers which delight humans and bees and butterflies alike.

Masses or rich blue flowers atop dramatic silver foliage.

Ceanothus griseus var. horizontalis 'Diamond Heights' is a low-growing, ground covering California lilac with gold foliage.

Ceanothus velutinus is a beautiful white-flowered species related to the California lilacs with aromatic foliage.

Ceanothus 'Lemon Ice' is a hardy, upright, evergreen shrub with variegated green/yellow foliage and fragrant blue blossoms.

Centaurea 'Colchester White' has bold, thistle-like, lavender-pink flowers and large, finely cut, silver-grayish-white foliage.

Centaurea montana, the perennial bachelor's button, is a cottage garden classic with feathery, royal blue flowers with dark pink centres.

Centaurea 'Pulchra Majora' is a cool bachelor's button with dramatic artichoke-like buds and silver foliage.

Cercis canadensis 'Covey' Lavender Twist is a special weeping form perfect for small gardens and containers.

Cercis canadensis 'Hearts of Gold' offers dramatic golden foliage that emerges flushed with orange.

Cercis canadensis 'Ruby Falls' has weeping branches with striking burgundy purple foliage.

Chrysanthemum Mammoth 'Coral Daisy' is a long-lived perennial with large, semi-double,coral-pink flowers.

Chrysanthemum Mammoth 'Dark Pink Daisy' is a long-lived perennial with large, deep pink to mid pink petals.

Chrysanthemum Mammoth 'Lavender Daisy' is a long-lived perennial with semi-double, lavender-pink flowers.

Chrysanthemum Mammoth 'Red Daisy' is a long-lived perennial with semi-double, deep red to fiery red flowers.

Chrysanthemum Mammoth 'Yellow Quill' has lemon yellow quilled petals around a golden yellow centre.

Chrysanthemum weyrichii is a perennial ground cover with late summer pale pink daisies.

Chrysogonum virginiana 'Quinn's Gold' has flowers opening bright yellow and maturing to cream.

Chrysogonum virginiana var. australe or goldenstar is a an evergreen ground cover with single yellow flowers all summer long.

Cirsium rivulare 'Atropurpureum' is a rare perennial with long-blooming, lipstick red, thistle-like flowers.

Cirsium 'Trevor's Blue Wonder' has unique, rich purple, thistle-like flower heads.

Citrumelo (xCitroncirus) is a cross between a grapefruit and the very hardy trifoliate orange (Poncirus trifoliata) and tastes like something between the two. It is hardy outdoors on the west coast.