We stared by building boxes out of 1x6's, adding square supports in the corners. Each board is attached with screws so we can easily take the boxes apart at harvest. We used untreated wood knowing the boxes would probably only last a year or two.
Before placing them in the garden, we dug out a trench about 3 inches deep so the boxes would be partially below ground level. Then we filled them up with dirt and planted the carrot seeds.
Then we patiently wait all summer while everything else grows and the carrots take their time. I'd like to saw we did an excellent job pulling weeds and all that maintenance stuff, but it didn't happen. At some point during the late summer, we realized that the critters (rabbits maybe?) got into the garden, which is completely fenced in with chicken wire. They found one row of carrots and completely devoured all the plants. Yep, an entire row of carrots-gone. They had got into the second row, but not all the way. I don't know what stopped them, but I was glad we were going to have a least a few carrots. Fast forward to mid October and the looming first frost. It's time to harvest the carrots!
I sent the husband out to take the screws off the corners. Don't mind the massively overgrown weeds all around.
After removing the bottom board, we just pushed the rest of the box backward so it was easy to move the dirt away and grab the carrots.
After a quick rinse and trim, we ended up with a decent amount of carrots. Next year, I'm thinking about adding chicken wire over the top of the boxes so the critters can't get in there and dig up the veggies!