And I agree with mysunnyboy. It's nute burn in my experience. My first grow I over fed and they looked just like that. It'll still produce bud that get you high but won't taste or smell good.
Tell us more about pot size, how much DG per gal you feed and how often.
One more thing to keep in mind... Miracle gro soil gets hated on a lot around here. It can be good soil if you understand how to use it. There are other soils with better drainage so they tend to work better, however like I said it should still grow good pot. In fact I had to use my wifes Osmocote (owned by scotts the same corporation that owns Miracle Gro) soil as a last resort and those plants seem even healthier than the ones in my Roots Organic soil.
The main concern with these soils is that they have nutes in them already. They advertise that they have enough for months of feeding before you'd have to add your own nutes. What I do is watch very carefully for my bottom leaves to start showing any signs of yellowing (nitrogen deficiency) before I start feeding a Very small dose of Dyna nutes (1ml per gal with every watering) and will not up my nutes any stronger unless they begin to look deficient again.
Hope this helps.
Now who dies???