Just bought some western red cedar fence picket boards from Lowes. Some of these are very heavy and full of moisture and others are very light and dry. The boards are 1/2" thick by 5.5" wide and 6' tall. I'm wondering how how long it will be untill the wet ones are dry enough to stain and is there any special way to dry them. Right now I put them leaning against my house facing South. The forecast for the next few days is clear and sunny. I could also put them in the basement with the dehumidifier on maximum which should bring the humidity down to about 40%. Or I could put them in my sunroom which can get into the 80 to 100 degree range if I don't open the windows and it's sunny out. I'm not in any terrible hurry so a week or two of waiting won't be that big of a deal.
I certainly wouldn't recommend leaning them on anything. They're likely to bend on you.
Honestly, I think the best thing you can do is get your boards installed as soon as possible. Being 1/2" thick, it will only take 3 or 4 dry days for them to lose the bulk of their moisture content and be ready for staining.