Raymond wrote:I would like to put it into a grow bed to get some girth happening.
First, nice trunk - especially the lower half. Ironically it's nicely styled as an Australian native style. (generally upward moving branches, nice random movement) An alternative, more traditional arrangement is shown in the
Art of Bonsai Juniper gallery (below).
The danger
The danger that you have is, for development, you have a lot of greenery at the top, which is what drives juniper growth.
The danger is that with this the top of the tree will thicken up, not the bottom - so you'll loose the taper you have.
Raymond wrote:When should I put it in the ground?
Whenever there's no frost or 30+C and windy.
But you don't need to put it in the ground - a large pot/box will do quite nicely and will, if filled with proper mix, result in faster growth than the ground. Especially if your ground has a tendency to stay wet - junipers don't like wet feet.
Raymond wrote:Once I have grown the necessary genitalia to go ahead with it, what sort of care will it need?
Less than it needs now. Make sure you stick a plate/CD/piece of crock directly under the tree so that you don't get roots heading straight down.
Junipers in general
Every group of trees we use (maples, pines, junipers, plums) have different needs - fortunately there is a bucket load of information out there - especially now that there have been several waves of westerners doing apprenticeships in Japan and blogging about it.
There's lots out there to read about:
Itoigawa Workshop: Start to Finish
Never Pinch Junipers!
Shimpaku Clean Up and Styling