It can depend on what Miracle Gro formula you used. Some of the stuff like Nature's Care Organics etc will be well exhausted by flower time and it would be good to find a good fertilizer or some good top dressing to put out a couple weeks early. Some of the Miracle Gro formulas have very long time released pellets in them that can last a good while then dump nitrogen a couple months later. If it were this type of medium used, I might consider something heavier in PK after flowering starts. A lot of people here know a lot more than me, but I am relaying to you more things I have learned from growing a lot of different plants outside for years and years. I stopped using Osmocote and Miracle Grow time released things a long time ago because I learned they stripped me of the control I wanted, and sometimes dumped nutrients at times I didn't want them. Mainly though pay attention to your plants, they can tell you what they are in need of.