I'm not opposed to using appropriate chemicals but I am opposed to throwing chemicals at everything. I checked a box of Miracle-Gro I have and it shows:
Nitrogen - 24%
Phosphate - 8%
Potash - 16%
+ bits and pieces of others
It's not that bad a general mix, but different plants need different things. Nitrogen is good for corn, but too much nitrogen can cause some plants to grow a lot of vegetation but little fruit. You need to know what your plants need so you can provide what they need instead of something that will make them look like they are doing well but really won't help them produce what you want. A soils test could tell you what your soils are deficient in. Your county cooperative extension agent can help you with that, probably pretty inexpensively though it will take time. You can find them under county government in the phone book. Hope that made sense.
You can over-fertilize too. I find I have to be careful not to burn melons, squash, cucumbers, things like that. Miracle-gro is pretty strong. A little could go a long way.
I don't know how big your garden is. A 20 or 40 pound bag of chemical fertilizer may be a lot more cost effective than Miracle-Gro. Don't get the weed-n-feed though for your garden. The chemicals in weed-n-feed would consider grass good and your garden crops bad.
Since you added the shavings along with the chicken manure, my guess is that you did not have enough nitrogen to decompose the shavings (the carbon-nitrogen ratio was too high), so the shavings took available nitrogen from the soil to aid in their decomposition.
Depending on what your crops are and how big an area we are talking about, I'd be tempted to get a bag of say 10-10-10 fertilizer and carefully feed the plants. Maybe even something a little higher in nitrogen.
Hopefully the real experts will weigh in. Good luck!