In the last Shibui Bonsai post I showed how I start root over rock trident maples. They are then planted in large pots or boxes in the nursery for the summer. I find the nursery is the best place because the trees get regular water that can trickle down between the rock and foil and keep any of those shorter roots alive until they grow long enough to reach out the bottom and into the potting mix.
I generally leave these trees untouched for the entire summer. More growth up top means more root growth below soil level and that’s exactly what I want.
Here are a couple of the root over rock trees I started last year.
This is the part I really look forward to. These trees have been growing all year but we can’t see what is developing below the soil. Will the results be great, OK or terrible?
At this stage, after just a year of growth, it is still possible to move some roots if necessary to improve the look. You can see that in many cases, new white roots have started to grow down the rock. In some cases I’ll remove some roots if it looks like there are too many. I want to see that there is a rock in amongst those roots. Too many and, as the roots thicken, the rock will be completely covered.
Now the trees are wrapped again with fresh foil and planted for another year of growth and thickening. All of these had plenty of roots from the bottom of the foil so could go into the grow beds for maximum growth. If few roots have extended to reach the bottom of the rock I’ll put those back into the nursery for another year of intensive watering.