Lift up the low ends until level and block it up. Set the box right where you want it, allowing for pathway widths. Set a level in the middle of the long span, on top of the board. Go to the low (downhill) end and lift it until you see the bubble centered in the level.
How to build raised beds on a slope
Hillside Stair Dig
Frequently Asked Questions
How do you level landscape timbers on a slope?
Lay the second row of timbers, staggering the seams above the timbers below. Pitch the second row, and every subsequent row, into the slope by 1/4 inch from the row below it. Drive galvanized spikes between the first and second rows to secure the wall. Predrill the wood to make the work easier.