Q.Garden Beds
I am planning on building some raised garden beds for a vegetable garden. Plans are 8’long by 2’wide by 8″deep. I plan on tilling the ground underneath the boxes. I am wondering if 8″ is deep enough for the boxes since the ground will be open underneath them and if 2′ wide is adequate. Also what should I use for soil to fill the boxes with. Trying to keep on the inexpensive side to fill the boxes since I am doing 8 boxes. Not sure to use top soil, potting soil or a blend and what about organic material from around the yard to help fill the box such as twigs, leaves palm fronds and such.

Certified GKH Gardening Expert
I do think that you have the right idea, and what you suggest would be ideal. Tilling the ground underneath will greatly improve the rooting depth, as well, as some plants will far exceed the depth of the bed.
As far as soil goes... We cannot recommend specific brands, but I do think that a mixture of topsoil and potting would be good. However, if you use organic materials from the yard, I would make sure that it is well composted first.
Here are some articles that will help:
https://www.gardeningknowhow.com/edible/vegetables/vgen/raised-vegetable-gardens.htm
https://www.gardeningknowhow.com/garden-how-to/info/pros-and-cons-of-raised-beds.htm
https://www.gardeningknowhow.com/edible/vegetables/vgen/raised-bed-soil-depth.htm