Hi Kurt,

Welcome to the forum!

Most citrus are self-fruitful (don't need to be pollinated), so that's likely not your problem here. Another thing that citrus do is self-thin their flowers and fruit based on how much the tree can support (also a factor of how dense the leaf canopy is). It sounds like your tree is of fruit-bearing age, and it's size would suggest it should be holding onto more fruit.

So there are a couple other things you may want to consider:
1) You may want to change your fertilizer to one specifically formulated for Citrus with NPK ratio as close as you can find to 5-1-3 and containing micronutrients, namely Fe, Ca, S, Cu, Mn and Mg. I use GreenAll's Citrus & Avocado fertilizer with good results and apply 3 times a year on Valentine's Day, Memorial Day, and Labor Day (makes it really easy to remember). There are many here who have not had good success with fertilizer spikes...
2) I've lived in Santa Cruz, so I know how that the marine layer can really influence temperatures there. Where exactly do you live (do you get sufficient sun/warmth), and do you know if you have an orange that does well in your micro-climate? I've read in the Cloudforest Cafe forum of someone in the S.Cruz mountains having great success with Cara Cara, for example.

Best of luck, and keep us updated!

Tim

Don't stress. Citrus are self-thinning and will drop any fruit the tree cannot support. The reason you had fruits when you bought it is because the grower "forced" the tree to produce fruit to sell it; it is unscrupulous in my mind, but that is business.
Your tree is still young; but if it is setting fruit you can be of good spirit.
First thing is I would lose the fertilizer spikes; they ae inadequate in almost all scenarios for citrus; again, the word unscrupulous comes to mind concerning the people who sell them... they don't believe they really work; but the consumer buys them because they look easy.
Get some decent citrus fertilizer and fertilize your tree 3 times per year, water it deep about once a week; and keep a good thought .. you will get fruit. Oranges are very forgiving.

Tim, look... we're on the same page!!

John