Northern California Coastal & Inland Valleys
The end of August is the time to switch cymbidium orchids from a "grow" formula fertilizer to a "bloom" formula. Switch to 0-10-10 or 15-30-15 and apply monthly. Keep and eye out for slugs and snails hiding in the foliage.
Late summer and early fall is the mating season for the yellowjacket wasp. These stinging insect pests are especially active now. Yellowjacket nests are usually in the ground, so be aware when you are working in the garden. If the nest is upset, the wasps swarm. Set pheromone traps and keep pet food indoors.
Deep Water Landscape Trees
Use a soaker hose to apply water to drought stressed landscape trees. If trees appear wilted or dusty, a deep drink of water will perk them up. Lay a soaker hose around the drip line and let it run for several hours or overnight. Redwoods especially appreciate a late summer pick-me-up.
Allow Perennials to Go to Seed
Late summer is the time to allow your perennial flowers to produce seed heads. Stop deadheading now to signal the plants that it's almost time for bed (please excuse the anthropomorphism). Ripe seed in late fall is a treat for migratory birds.
It's fire season. Be prudent and move wood piles away from buildings. Wear gloves -- spiders live in wood piles. Mow wild grasses that are close to fence lines and remove overhanging branches from roofs.