Hi, Gigi. The prostrate form can be styled in an upright position, but it will take forever to form a trunk, so it's better to take advantage of the prostrate habit by electing to go with a cascade or semi-cascade style tree. If you're wanting to make the other style trees, the upright varieties are best for that and will form up a trunk in speedy fashion (by tree time).
Typically, the upright plants are allowed to grow wild for a time until you are able to define an interesting trunk line.
The tree below has had about 3/4 of it's branches/foliage removed in order to define an interesting trunk line.
Below, you can see a large part of the main trunk was chopped off in order to give the tree rapid taper, which adds to the appearance of age:
My initial thought was that the part wired upright to the left would be the new leader, but the branch it's attached to which is growing to the right is too thick. I needed an alternate plan, so I allowed the plant to grow:
Below, you can see where I removed what I thought would be an extension of the trunk in favor of another branch further to the right, which I had left as a "just in case I want a different trunkline". Now, the trunkline is set, taper is good, and I have the first 3 or 4 branches in an appropriate position, ready to be grown out. From this point forward, it's all about refining the tree.
I'm lucky in that this tree offers an alternate front view (below). Most bonsai are designed to be viewed from their best side, referred to as the front. This one has 2 potential fronts I'll need to choose from later as the tree progresses.
Below is a tree in the raft style. It has several trunks, but they were all once part of the same branch. I cut the branch off a much larger tree and positioned it on top of the soil where it rooted. It doesn't look like much, but it was an instant bonsai start.
In the image below, it's just beginning to come together
Another now/later look:
And, 3 years in the life of a portulacaria:
Al
