Raised bed for herbs and flowers

Raised bed for herbs and flowers, with rounded corners.

Let's start with the final result, cedar raised beds, for herbs and flowers. With rounded corners.
This weekend project began with this drawing. The corners are not actually round here, but only because that's way too difficult to draw.
Some measurements and calculations. I need to know the total length of that rounded 2×4, which will contain the two sides and the quarter circle. Also, by comparing the quarter circumference on the outside and on the inside, I know how much wood needs to be removed to get a 90 degree bend. This length, divided by the width of the saw blade is approximately how many cuts I will need.

EDIT: Some details about the measurements. Let's use the top drawing. The rectangle is 36" by 64". The radius of the rounded corner is 18", this is half of 36 so it looks balanced. The circumference of the 18" circle is 113.1, so a quarter is 28.25. So the total length of that piece of wood is 46+28.25+18=92.25". (I also need to pieces of 36" and 64" for the other sides).
The bent piece will have the cuts in that 28.25 section. How many cuts? If I compare the quarter radius of the circle r=18 and another circle r=16.5 (the wood is 1.5" thick) I find a difference of around 2.33 inch, my saw blade is 3/16", so that's 13 cuts. I used about 20 cuts, this is why the seams don't close perfectly. A thinner saw blade (hand saw) would help here, more smaller cuts is easier to bend.

Making these cuts on the table saw. I cut almost all the way, leaving 1/4 to 3/8 to be bent. I believe that's called kerfing.
Trying to get the spacing as equal as possible.
Ok, this really does not bend much. I could make the cuts deeper but then it will crack.
So here's the trick, wrap in a few kitchen towels, then pour boiling water, wait a few minutes.
Now it bends easily.
Clamping everything inside a square frame while it dries, I also added some glue in the seams.
The wood does't hold yet, I attached both ends with a plumbing metal strip to keep it from moving before it is screwed to the final assembly.
Some plastic wood to fill the holes.
Now my two rounded corners are done and the other pieces are cut to length. Upper level is a 2×4, lower level is a 2×6.
The final assembly will look something like this. Added a banana for scale.
That banana won't go to waste.
Assembled and held in place with some stakes. This doesn't need to hold any weight, I just want it to stay in place.
Then filling it with a few bags of soil and compost.
This is what it looks like completed.
Herbs will be planted soon. But not yet, the snow just melted here.
Source : ed77 from Reddit