Over the last several years we have been starting some Trident maple projects by growing multiple cuttings through holes in a tile. Rooted cuttings are inserted from below. The group is planted for vigorous growing. If you try this, be sure there is plenty of soil above the tile for the new roots. This first pictures shows cuttings that have been grown for a year. There are strong roots below the tile, and new roots established on top of the tile.
New roots will issue below the tile.
Trees are planted and grown vigorously for a year or 2. We are finding the best container for this work is the Anderson tray.