Choisya ternata.—This only needs thinning after the flowers are over and old wood removed.
Cistus.—Those which are hardy of this genus should be cut back each spring while in a young state, but when they have attained a flowering size no pruning is required. The cutting back of young plants induces a bushy habit, and also keeps them from weakening themselves by blooming and seeding.
Clematis.—The garden forms of this genus are divided into two sections, of which C. Jackmani, C. lanuginosa, C. Viticella, and C. aromatica (C. cærulea odorata) are the types of those which flower on the young wood, and which require cutting back close to the old wood in the winter; while C. florida, C. patens, and C. montana are the types of those which flower on the ripened wood of the previous year, and merely require a thinning out of weakly or unnecessary growth. Of species other than those mentioned above, C. Flammula, C. paniculata, and C. Vitalba flower on the young wood; and the remaining species are either herbaceous or flower on the old wood.
Clerodendron trichotomum.—Thin in spring.
Clethra.—These practically require no pruning, but long shoots may be shortened and weakly ones cut away with advantage.
Colutea.—These make better plants and flower later if they are cut back every winter. C. istria (a rare species) should not be cut down if flowers are desired.
Cornus.—The strong-growing shrubby Cornus, such as C. alba, C. Amomum, C. Baileyi, C. pubescens, and C. stolonifera require an annual thinning out, and those with brightly-coloured stems should be cut down every spring for their effect during the following winter. The remaining Cornus require little or no pruning.
Cotoneaster.—The large-growing species should be pruned in late summer, but only sufficiently to keep them within bounds; C. Simonsii requires cutting down annually while young to make it bushy, and the dwarf-growing kinds are best left alone.
Cratægus.—Keep the heads well thinned out to allow light and air to the centre of the tree. This should be done in late summer.
Cytisus.—These require very little pruning, with the exception of C. nigricans and C. capitatus, which flower on the young wood, and should be cut back annually. The other species and varieties make better plants if they are cut down each year while in a small state, but they should be left alone when they have attained flowering size.