I like the way you think!
You are correct. Farm raised cultivated ginseng is normally harvested at four years of age. There are several reasons, but I think it ultimately boils down to risk. Shade costs about $10,000 per acre. Then add seeding at about 80-100 lbs per acre, nurse crop seeding, growing clean straw to avoid weed problems, spraying for weeds, spraying for disease, irrigation, drainage where necessary, fumigation, and many other incidentals such as labor, and you can see ginseng farming is a big money game.
One of the key components is that ginseng farmers will not grow ginseng where it has grown before. Replant failure is a mystery for the most part, although there are theories. If you are putting the kind of money in they are, and must wait and fight disease and weather for four years to recover any of it, you would not do anything that jeopardizes your chance of a good return either. So, once you grow ginseng on a field, you rend new ground or buy a new farm. That gets very expensive.
The farmers I know work with potato growers. Sometimes the potatoes go in before most always after ginseng. They often grow their rye which they use for straw mulch before the ginseng on the same fields.
So, planting trees might cause more trouble than it is worth for a lot of reasons.
Now, more generally, they fertilize farm raised plants to death. They are very big and very smooth. But, cultivated ginseng is not the same market at all as wild ginseng. The two go by very different standards. Big chunky roots that are not branched is good for cultivated ginseng.
I"m sort of in a hurry at the moment, and guess I might have rambled a bit...if I didn't really get to the heart of your question, just point me in the right direction and I'll give it another shot
