"I know this issue has probably been discussed here before, I just cant find it."

Just scroll down through the posts.....or do a forum search. This topic has been discussed endlessly!!

First, let's establish what sort of planters you are deaing with :-) Do they have a solid bottom or are they raised beds in contact with ground soil. It makes a big difference!

FWIW, although packaged commercial potting soil mixes are used by many with reasonable success, they are by far not the best choice. Most tend to be excessively water retentive and with too small a particle size so they collapse and compress in a short amount of time and impede good drainage and proper aeration. For a solid planter or container (with a bottom with drainage holes). the 5-1-1 mix would be my recommended choice. If they are just raised beds in contact with garden soil, then they should be filled with just garden soil as well, although most choose to enrich that soil with compost or other OM, just as you would ingound plantings.

If you need more than just a few cubic feet of soil to fill bottomless planters/raised beds, then look at bulk soil providers. Most will sell garden planting mixes (perfectly suitable for this purpose) by the cubic yard at less than half the price of any bagged product.