I think it is not just fertilization, but a combination of factors. I learned over the years that working the soil is very important, so I till it 2-3 times, as deep as possible, before planting. My soil is clay, so I amend it with top soil every other year, and some times I add some Scott’s garden soil (which has fertilizer in it). This is also the sunniest spot in my yard, so it gets > 8 hours of sun every day. Finally, I add a spoonful of solid fertilizer in the planting whole and 8 weeks later I start adding liquid fertilizer every 6 weeks till The end of the season.