I have just stripped this garden of the old mulch and waiting for new untreated playground mulch to be delivered. I went with this idea (from Mother Earth News) because the thin top soil is hiding rocks the size of our Buick. The bags are from Lowes store at $1.50 per bag. This will be the third year for this garden. Got a little horse poo to mix with the bagged dirt. The nice thing - no weeds!!
The bags are just clean cheap top soil. Yes, poke 3 or 4 holes in the underside for drainage. Too many holes and the bags dry out to quick. When the mulch is around the bags this keeps the soil at a even temperature. The stand in the middle is a strawberry box. This is lined with white plastic, filled with dirt and holes cut in the sides for the plants.
On the horse manure. Not sure if you used it yet in bags in the past, but be careful with how much you use. The bags are confining the soil, and it will also confine the poop of course. Careful of the amount of hot manure you add in to them. If it's "green" manure (fresh), be even more careful. DOn't want to burn em up.
Looks good. Looks like some onions in a couple already ?