You definitely need to use some fertilizer, first year and every year. If you use standard chemical fertilizer for flowers, then small amounts a few times during the growing season. Slow release fertilizer you need less often. I've had salvia rebloom in pots over several years. I start potting into larger size pots after one or two years for best results, depending on the species.

Most salvia in pots also need consistent moisture for best blooming.

I have also have Salvia in pots that are onto their 3rd and 4th summers. I agree that fertilizing is necessary; I use a dilute solution every other watering... but at least once a month.

thank you, do you think they wd like fish emulsion? i happen to have it on hand.

Go ahead and use your fish emulsion, but at HALF the recommended strength, no harm there.
You didn't mention what type of Salvia you are growing. Different Salvias have different needs, from soil to water, but anything you grow in a pot is going to need REGULAR FEEDING to produce blooms and healthy growth.
Your pot size is what I'd call on the small side if you do not intend to re-pot yearly (again, depending on it's variety)
Your best choice if you are not the type who will remember to faithfully feed your plants, is a time release fertilizer like Osmacoat which will feed anywhere from 3-6 months depending on the formula. See the label.
In the Bay Area you should have almost continuous growth.
Liquid fertilizer should be applied at half strength for any potted plant.
Salts also accumulate in the soils of potted plants which needs to be flushed occasionally to promote healthy growth. Do so by soaking entire pot in fresh water until saturated, then draining. After draining, water heavily until water free-flows from pot drain hole.
Hope this helps.