A lot of growers advise to stay away from MG products. it's not for cannabis. Those spikes are time released nutes. you want to be able to control the amount of nutes your plant will be absorbing or you'll eventually get burned by nute burn. I'd say go with organic soil (with some vermiculite,perlite etc), lose the spikes, and get some good nutes online.
Yah I have to agree, I don't really think that miracle grow is the best for cannabis. I think a lot of people just use it because its easy to find at the store. The truth is that you also probably have a hydroponics store in your town/city. Here you can find the stuff that is somewhat used for marijuana. Google it man you'd be surprised! But yah ask the employee and they can point you in the right direction.
HAH...yes that would work perfect....."Excuse me sir but where are you marijuana growing supplies?" haha
Finding your local hydro store can be a bitch, at least all of the ones i've ever used always have ridiculous names like "paradigm", but they are always very cool and open to helping you too, so dont be worried you'll sound like a noob if you go in. The guy at my local store is really cool about helping out with stuff, and i've never had someone act suspicious, even when it feels pretty clear what we're discussing (haha i'm not advocating for you to be careless here, do be very careful! this is very much so illegal still in most places!). If you're looking for a soil idea, I just buy a bag of Fox Farms Ocean Forest soil, and a bag of Fox Farms Light Warrior, and mix them to about a 50/50 ratio. Very simple and works incredibly well, but my store only sells it in the bulk sizes, so its kind of expensive at first, but you get plenty of it. You might also want to get some "ornamental transplant soil and root innoculant with mycorrhizae" to put into the soil to boost the root development, its just a powder with some spores and other good stuff in it, really easy to use. Some people probably say not to use that last one, but I feel like I always notice much better root development on transplants if i do use it, so take it or leave it as its not incredibly important. (made by Age Old Organics) Remember, if you dont want to grow ditch weed, dont use ditch dirt! good luck on the grow man! edit - and hey, just make up some dumb excuse like you got an aero-garden for christmas from some cousin or whatever. Like I said, i've never had to use one, but its always good to have a story so you're not fumbling for words should someone at the store give you the 5th degree.
I dunno man, I've been using Miracle Gro for "Trees n Shrubs" and my plant is doing great. But I don't think this one has those time-release nutes. Either way, I think it's more how you tend it, in the end soil is soil. Just those damn time-release nutes that are bad. And I also have a plant that is in non-MG soil and the growth seems alot slower after 2 weeks.
The main point i'm trying to get across, if you are in a situation where the only soil you have to use is MG, it's not THAT terrible... I couldn't find any stores that had any brand name soils.