There isn't a schedule for fertilizing :-) Fertilizing should not necessarily be considered a routine garden chore. Typically the recommendation is not to fertilize unless or until there is a need. Determining the need is best done by having a professional soil test or closely monitoring the appearance and growth of your plants. Then, supply only those nutrients that may be lacking - no more, no less. The concept that a productive, healthy garden requires routine and frequent fertilization is a marketing myth perpetuated by the fertilizer manufacturers. Established landscape plants - trees, shrubs, perennials, groundcovers - are typically able to get all the nutrients they need from existing soil conditions. Not from a box or hose-end sprayer :-)

Often, gardeners who routinely mulch their planting areas with a good quality organic mulch like compost, composted manures or wood chips find that there is no need to provide any additional fertilization - the mulch supplies all needed nutrients.

The exception to the fertilizing program is anything grown in a container (as opposed to in the ground) - these will need repeated fertilization throughout the growing season - or harvested edible annual crops, which both require as well as pull high quantities of available nutrients from the soil.

Thanks for your quick response, Gardengal...Such a load off my mind and I don't have to feel guilty anymore.

Can you suggest where to get soil tests done in the Seattle area?

Soil testing for home gardeners used to be handled through the cooperative extension service but the demand in this state (and others) exceeded the ability to do low cost tests and now all WA soil tests are referred to independent professional testing labs.

You can find soil testing kits at any nursery or hardware/box store and while relatively inexpensive, I'd suggest you save your money :-) They are just incredibly inaccurate, with the possible exception of the pH test. A professional soil test is moderately more expensive (around $15-25 for a basic) but well worth the investment for the detailed results and recommendations.

I've included an extension service link that outlines all the details, including an exhaustive listing of testing labs.

Here is a link that might be useful: WSU soil testing info