Soils vary, so you should sample your soil and have it tested before choosing a fertilizer.

How do your plants look? Is there some reason you think they need more fertilizing?

This is a question that comes up regularly on various forums and I think it is indicative of the success of the brainwashing/marketing campaign fertilizer companies are promoting. "Use our product every week or your plants will look like crap". Nonsense!

Regular periodic fertilizing of plants in the ground, specially with some chemical formulation that is dissolved in water, is just not necessary and in many cases will be counterproductive. It's like junk food with kids - a big boost in energy levels that are not sustained and that typically create downsides like too lush, leggy growth, often lack or reduced flowering and attraction of insect problems. Side effects like run-off or leaching into groundwater, salts build-up and declines in soil organism populations can also be a problem with too frequent or unnecessary fertilizing.

Concentrate on keeping your soil quality high. Mulch regularly with a good quality compost and in addition to needing little in the way of any supplemental fertilizing, you will encourage beneficial soil organisms, replace needed organic matter, help to conserve soil moisture (less frequent summer watering) and supress weed development.

Some plants that are heavy feeders (high nutrient uptake) - roses, clematis, lilies - will benefit from an early season application of a slow release fertilizer, but most plants will perform very well without copious amounts of fertilizers applied over the course of the season. Woodies are best served by a late season application, if necessary. The exceptions are container plantings which have different needs and requirements.

If your plants are not performing well, then follow Ron's advice - have it tested and augment what is lacking. But periodic mulching or top dressing with compost - your own or a purchased commercial compost or composted manure - will preclude the need for much additional fertilization, if any.