Do the boards need to be planed?

[Maijan]

I was thinking of burning the boards for the raised garden beds that I'm building. The question is whether they need to be planed? Why if so? And what happens if they are not planed? (Borrowed image)

 

[klaskarlsson]

I'm planning to burn the boards for the planter boxes I'm building. The question is whether they have to be planed? Why if so? And what happens if they are not planed? (Borrowed image)

If the side you are burning is not planed, I think you might more easily get the board to catch fire (due to the fibers sticking up), but if you brush it off in good time, it should still work.
Then you'll probably get a bit more texture on it. Outdoors, that might be bad (dirt and moisture can get stuck, and mold can grow, etc.), but I have no idea how bad it could get.

 

[z_bumbi]

You get a more uneven appearance with unplaned. If you're planning to burn a lot and then brush off the soot, it matters less. The simplest way is to test a few different pieces and degrees of burning. From the little I’ve tested, it's not entirely easy to reach the right level. Have a spray bottle with water (for embers on the boards), a bucket of water, and preferably something else to extinguish with.