OHHH NOOO, not Miracle Grow soil and nutrients. Not putting you down here as you are new and most likely didn't know. Never use MG soil unless it is the seed starter that has no nutrients added. Never use MG nutes, ever. The problem is that MG nutrients are too strong and aren't formulated for Marijuana. MJ is a very finicky plant that likes its environment to be in a narrow ideal (nature is different, without going into a 5day botany lecture, it just is). What is happening now is there is a lot off "stuff" in the miracle grow that the MJ doesn't use, so this gets left behind to build up and create toxic lockout.
Now there are many who will tell you that you CAN use MG to grow MJ. That is true just as you CAN feed your cat, dog, and fish hot dogs all their lives. But they will not live healthy or long.
Fortunately for you so ffar, your plants have been doing ok, but now the buildup problem is beginning to show. I highly recommend that you get a container the same size as your planters and use that size to water the plants with 3x the amount with fresh water. This will wash out all of the MG nutrients in the soil. (Save the MG ffor the flower beds) Order yourself a couple things from Amazon or go to the nearest hydroponics store. You need General Hydroponics' Flora 3part, pH adjuster (up and down) and I recommend you get a decent pH meter and a decent TDS meter. You will need these to make sure your water and soil pH are kept in the right range. The TDS meter will tell you how much nutrients you are putting into the water for feeding the plants.
Now if you are "old school" and just want to do the "old fashioned garden soil"(now known as "organics"), then you can do that, but again MJ has very specific nutrient needs. You can stay with the same soil you have and get some Dolomite Lime and mix into the soil, and get some dry/liquid "organic nutrients and feed them once a week. If you go the "organic route then you will not need to have the TDS or pH meters as the organics and lime will balance the pH.
You can also look through the Organics thread and see how to make your own soil and just supplement it with microbe/nutrient teas.
If you would like some 1 on 1 help with this, just PM me and I will be glad to help you, no cost or security issues.