Is it possible to save your existing lawns? The answer is yes. The right time to seed is early spring or fall, so right now is perfect. To start you will need to remove weeds and old sod and loosen the soil. Following this you can use a core aerator for large areas or a digging fork for smaller areas. You will need to fill in low spots with top soil then add your seed. Selecting the right seed for the site is important. You will need a shade blend for those shady areas and I like to use a fescue blend for our Northern California climate.