The Miracle Gro test was done outdoors. My current plants will be under 12 40w/200w Daylight CFLs divided into 2 - 2'x4' spaces .... Currently only burning 1 bulb per seedling ... very satisfied w/ Daylight CFLs for all stages of a grow.
I do believe it refers to 'soil' or other solid (ish) 'medium'.
As opposed to 'hydro', would be how I interpret.
I'm still old school pot and 'soil'. As mentioned already, the potential cons
can be (are if you are careful) pros...
Getting soil temps up in black pots under a plastic tarp
hot house is unbeatable in a sort of a raised bed game.
Yes, it requires monitoring with a moisture meter. (<$10 USD)
I prefer to add perlite which while a tad pricier than vermiculite,
since I re-use the soil in different vegi garden later. Vermiculite
breaks down much more quickly, so perlite for all that hand
work mixing my own growing 'medium'.
Since I started using a moisture meter in the soil, I'm watering less and the plants and I are enjoying it more. My opinion is that most growers, especially newbies tend to overwater, I know that I did.
Now I'm setting all the plants up with drip water from my tub / pump on a timer. I water one minute three days a week.
The top of the soil in the pot is usually dry, but the meter tells me that the soil is moist in lower half of the pot.
This seems to help prevent mites or other pests - and I have two fans blowing on the veg garden 24/7.