Hi Cora - The weak growth and leaning stems have nothing to do with the soil, roots or pot size, so don't go there. Thick stems and leaves are a result of having lots of light exposure at the time those stems are formed. Older stems and leaves that are already small and thin will not become thicker and stronger by increasing the light now. But there is a solution - one that seems to terrify people and is so often neglected. It's called pruning.
Any of the leggy, leaning stems can be pruned back easily. Healthy new growth will emerge on the pruned stems just below the pruning cuts and grow upward from there. If that new growth is exposed to strong sunlight from the outset, then the new growth will be strong and sturdy. By pruning you get to control the way that the Jade grows and how it looks.
The pruned off cuttings can be rooted in water or in damp soil after being allowed to air dry over night.
