The hows and whys of bonsai sand trays
We’ve always had a problem keeping our small bonsai from drying out, so we finally used a large bonsai tray with drainage holes and filled with sand or Turface. We set the small pots on the medium. Now when we water we soak the medium as well as the pots. This does a couple of things, it provides a micro climate with higher humidity and the tree roots grow through the pot’s drainage holes into the medium and have a larger reservoir of moisture to draw from. The secret here is to not remove the trees from the sand tray unnecessarily, disrupting their adventitious root system. For shows and exhibits you’ll trim those roots otherwise just set them back in the sand. The caveat is that the drainage holes will be clogged with roots. Periodically you should clean out the drainage holes. This is not usually a problem since excess water in small pots will evaporate instead of draining out.
We had so many of these sand trays sitting around that we took the next step and built sand troughs about six feet long from treated lumber and galvanized deck screws. We used 5/4” x 5.5” x 6’ lumber. We used three boards for the bottom set next to each other. There were enough irregularities to provide drainage without losing the medium. We used boards cut in half for the edges. Now we can space out our smaller trees to make a nice display.
I've been doing bonsai since the late 70's. I'm passing on what I've learned in those 35+ years. These are real life techniques and tips that worked for me, but, may not for you. Remember, this is free advice and worth every cent of it.