In general the best time to prune plants is after they have flowered but before they have put on a lot of new growth. For California lilac (Ceanothus species) and manznaita (Arctostaphylos species) this is especially important because late pruning removes buds for the next season’s flowers – and what a shame to miss out on these spectacular displays.
For plants that produce desirable fruits and seeds, leave the spent flowers so they can go to seed. Examples of plants with colorful fruits are toyon (Heteromeles arbutifolia), barberry (Berberis or Mahonia species), madrone (Arbutus menziesii), and summer holly (Comarostaphylis diversfolia)
Be sure to leave some seeds for birds, insects and other critters you wish to attract to your habitat garden. Wild sage (Salvia species) blooms in spring, leaving interesting dried flowers that are an important source of food for birds through the summer. California buckwheat (Eriogonum fasciculatum) is another very important food source. It blooms in summer and yields attractive dried flowers with some seed for animals in the fall. Prune sage in the fall or winter when they are just beginning to leaf out again. The exact time varies with the weather. It was early this year due to an early rain and some cool weather in the fall. Buckwheat can be deadheaded in the winter, and usually requires little pruning.
Matilija poppies (Romneya coulteri) flower from spring to fall. Depending on how much water they get, they usually go dormant in late summer and fall. When the leaves are dying back, you can remove spent stems nearly to the ground. This keeps an otherwise messy winter plant looking good so that you can enjoy its spectacular flowers in the spring and summer. Place these large and ungainly plants in the back of your garden beds so they will not be a focal point when dormant.
Prune back bunch grasses at the end of their period of dormancy. For example, prune deer grass (Muhlenbergia rigens), a summer grower, in May or June, water it well and provide a light application of fertilizer. The plant will spring back in about a week’s time, looking lush and green. If you prune it during the fall or winter, while it is dormant, you will have to look at a sheered mound for several months.
Deciduous trees should be pruned lightly, as needed, when they are leafless and dormant. You will be able to direct you pruning best when the leaves are not present, and it is healthiest for most trees to be pruned when they are not actively growing. With all mature trees, it is best to consult a licensed arborist.
Coast live oaks (Quercus agrifolia), should only be pruned in summer months, when their growth rate has greatly slowed. If you prune at other times of the year you can promote excessive, off-season growth that is susceptible to mildew when it is hot. Pruning of mature trees should be restricted to removal of dead branches and the few that truly weaken the plant’s structure, such as crossed branches. Removing dead branches, especially those dangerous to people or property, should be done when necessary. For all mature trees, very little live growth should be removed. In fact, many cities have strict regulations on tree pruning, particularly for heritage or native trees. They often require the services of licensed arborists, city permits and they may limit the amount of pruning of live growth to 10 percent or less of the entire canopy. Be sure to consult with city officials before pruning any oak or other significant trees.