With the inspiration of you guys, now I can manage to judge the root ball condition by just looking at the way the new foliage grows. I bought a Buddas Hand Lemon a year ago. I potted it up into 5-1-1 mix combined with some turface. This thing just didn't grow, just a couple of flowers here and there. The new foliage buds always failed to grow and turned black, and it gradually losing its old leaves. I know there is root problem, root pruning maybe. I just have to dig it up and have a look. When I dug it up, the original root ball is still the same, the roots are massive and dense, the old soil is peat base fine dust, not much left anyway. So I followed Al's suggestion on root pruning, I was kind of bold, I know most of the roots are not doing their job anyway, I removed the old soil, trimmed almost half of the old roots, soaked it for 15 minutes, then potted it into the gritty mix. Immediately I wrapped it up with a big clear plastic bag, sprayed soaking wet. Next morning, I found a couple of new foliage buds breaking. This never happened before. They always failed to break the foliage bud before turning back and dried up. This can't be because of the repot, right? It's just overnight. I can't believe it. Is this a coincedience?

My lakeview jasmine did almost the same thing. My friend gave me a tree form lakeview jasmine with a huge pot, most of the leaves on the twig end, I know it must be pot bound, so I repotted it, discovering that the tree only used about half of the soil, the old root ball was bone dry. After repotting it into gritty mix by removing the old soil, in about a week, it loaded with many new growth.