Most seasonal yard advice is written for climates with a real freeze and summer rain. We have neither. On this side of the bay the year splits into a wet winter and a long dry summer, and the maintenance calendar should follow that instead.
Late winter into early spring is the structural window. This is when to prune deciduous trees while the canopy is bare and the branch structure is visible, cut back dormant perennials, and get ahead of weeds before they seed. It is also the best time to build. Ground is workable, plants going into the ground now root before the heat, and crews are not fighting a July afternoon.
Spring is irrigation season, and it is the single highest-value hour you will spend on the yard. Run every zone, check coverage, replace broken and sunken heads, and reprogram the controller for the year ahead. Everything you fix in April is a brown patch you do not pay to repair in August.
Summer is about restraint. Mow high rather than short, because taller grass shades its own roots and holds moisture. Water deeply and less often to push roots down instead of keeping them at the surface. Avoid hard pruning in full heat, which stresses plants exactly when they can least afford it. This is also when a weekly maintenance schedule earns its keep, since a yard left for three weeks in July does not simply pause, it declines.
Fall is the reset. Cut back spent growth, refresh mulch to hold winter moisture and suppress weeds, and get ahead of drainage before the first real storm. Clear the drains behind retaining walls, check that surface water still runs away from the house, and deal with any grade that has settled. Winter here is not a dormant season for a landscape contractor, it is when badly built drainage announces itself.