The Forestry Forum

I just acquired a walnut tree crotch, and am considering making a table top or counter top out of it.
I understand that I need to dry it slowly. Do I need to mill it right away or let it sit whole for a while? I would like to have 4 inch thick slabs. Time is not a concern.

Mill it right now. 4" is a huge thickness for a countertop. You'll need shorter cabinets for that! I don't care for tables with that thick of top either. Starts looking like Viking furniture, or a workbench!

I think you're right on the thickness, now that I think about it.
Do I let it dry inside a barn, or outside covered up?

The less weather it gets, yet the more air circulation is better too. Lying in the sun very long, without restriction, might be asking for a twisted slab. Walnut's a stable species but always best to pin it down with weight. I use concrete blocks but depending on your situation, clamping or straps may be easier. I've seen people nail the wood down using system the holds it in place w/o nail holes in prime slab. The weight must be distributed! All said w/o going into all the gory detail. Some slabs could be simply leaned against a wall in a barn, others might twist. Powder post beetles love walnut sapwood, so a live edge slab becomes food for them. I've seen lots of air dried walnut that you could crumble the edges off with your bare hand after some years. Beware.
I'd saw ~ 2 1/4" for a counter top.

Regarding sawing thickness, we mill at different thicknesses depending upon the width of the log and the amount of defects in it. Typically if we want to net a 1-3/4" to 2" S2S dry plank, we will start at 3" milling thickness for logs less than 48" diameter.  3" will dry down to 2-1/2 - 2-3/4", and if there is any movement during drying we will have adequate room to S2S post drying.

Logs over 48" and logs with a lot of defects are milled thicker in order to have room for surfacing.