As far as soil amendments, nothing beats compost, compost, compost! Black Cow is good but does have the addition of manure which is fine except if you get a heavy rain storm right after you apply it, the manure can release a big dose of nitrogen all at once that can burn young plants. During the rainy season, straight compost is the answer, with the addition of a pelleted, time-release fertilizer (if you are allowed to fertilize during summer, check your County ordinance! We aren't allowed to here). Did you check with your County landfill, whether they have compost available?
The other amendment that has some good, slow release nutrient value is alfalfa pellets. (horse food) It's available in a 50lb. bag at your local feed store for somewhere between $12 and $16. I put a handful or two in the planting hole of every single thing I plant, and then broadcast the pellets throughout my established borders as well.
