How long for green poplar to turn brown under varnish?

[Warner Harris]

Will green poplar turn brown under a clear-ish varnish (GF Arm-R-Seal in this case) over time?

How long? 6 months? A year?

I bought some poplar for shop drawer fronts and after 3 weeks in my workshop they are still very green.

They aren't going to get much if any UV after installed. I don't really want to 'sun them' for fear of warpage, which would defeat the 'browning' if I have to plane them further after sunning.

Try this trick. Mix 1 TBL. of Oxalic Acid (I found this at Rockler Woodworking) .. https://www.rockler.com/oxalic-acid-for-wood-bleaching .. in a pint of water and use a foam brush to liberally apply to the green board. Like magic .. the green will turn to a beautiful pale brown right before your eyes. A second coat won't hurt. Let the board dry and sand down the raised grain caused by the water and you're ready for staining.

[Warner Harris]

Of course .. this oxalic acid procedure will only work on boards before they are stained and finished.