poor fruit flavor

Is there a lack of an element or elements that causes poor fruit flavor? I am growing 'Seascape' strawberries which are fruiting and have big, very red, but tasteless fruit.
I use Black Forest mulch and gro-power either 3-3-3- or 3-12- (can't remember the last number but it is indicated for fruits and vegetables.) I am worried because this year I planted a peach, nectarine and plum and don't want this problem to occur. Thank you! I live in zone 21 in San Diego.

I also live in zone 21 (North of you in Encinitas). I've had both very good tasting fruit as well as fruit that was blah..

If you water too much the fruit won't be as sweet. But I've also noticed that when I worked a lot of manure into my garden I've had MUCH sweeter more flavorful melons.

I like to grow strawberries in planters and I'm thinking of mixing the potting mix with worm castings and seeing if that improves flavor. Maybe I'll work a little composted manure in as well.

I don't know what the elements are that cause poor fruit flavor but perhaps a clue is that we have a hard time growing good broccoli here. Now what elements does broccoli require?