Here's an excerpt from the article:
The full article has tips on pruning as well to get the straightest wood. It finishes with his idea that most of the trees he plants he'll let grow and never harvest, just so one day some kid who's read a book can come along, find them and make a bow. What a great idea!To start a tree, you must first collect the seeds. Osage
orange produces a light green, inedible grapefruit-sized fruit
that contains hundreds of seeds. When the fruits drop off the
tree in the fall they can be collected, and the seeds can be
extracted. I prefer to let the fruits partially rot because fresh
fruits contain a milky, sticky sap that’s almost impossible to
remove once it dries. After letting the fruit rot, I pull it apart
and extract the plumpest, fattest seeds. I then fill a small pot
with potting soil and bury each seed half an inch deep. Keep
the soil moist and watered, and usually within two weeks
tiny seedlings will pierce the top. Seeds from other hardwood
trees can be extracted and planted as well.
From there the seedlings need sun and regular watering,
but don’t over-water them. About once a month I’ll give
them a nutritious drink of light fertilizer like Miracle-Gro. I
mix it rather weak however, because a strong fertilizer can
burn the leaves and kill the seedlings.
As the seedlings get taller I move them to progressively
larger pots to accommodate more expansive root growth. I
keep the seedlings in pots for a year, and then transplant
them outdoors the following spring after the danger of frost
has passed. Dig a large hole and mix a ratio of one-half potting
soil to one-half local soil and water it well. Carefully
separate the roots of each seedling and plant each one in its
own hole, spacing them at least six to eight feet apart.
Pretty cool hey?