In Creativerse, Ashenwood trees can be grown from Saplings.
Eventually Saplings will be added now and then.
Ashenwood Saplings will even appear now and then if you place blocks of Ashenwood Leaves on the ground and then pick them up again. It can take quite long though, since the additional harvest will happen completely randomly.
However, Excavators of any kind will not yield any Saplings when used on Ashenwood Leaves and/or Wood. Also, harvesting Corrupted Ashenwood and Corrupted Ashenwood Leaves will not lead to finding any Saplings, even though they can be purified into Ashenwood and Ashenwood Leaves.
To make trees successfully grow, Ashenwood Saplings should be planted/placed on (green) Grass or Dirt blocks. According to Playful, Saplings require moisture too, but tests did not confirm this. If you want to be on the safe side, simply place 1 block of Water or Mineral Water nearby.
Ashenwood Saplings also won't grow on most other kinds of soil, like Mud, Detritus, Matted Needles, Canyon Floor, Rocky Dirt, Dead Grass, Savannah Grass, Sand, Sandstone, tree Leaves or Mold - if you try to plant Saplings on these types of ground, a message window will appear, telling you: "Item cannot grow on this block type.". Ashenwood Saplings will not grow on Snow Caps, even though Elderwood Saplings will.
Simply take a look at the Ashenwood Sapling right after placing it. If it stays "fallow" (written in red letters) even after placing water nearby, you can just tear it out again; since no trees will grow at this spot.
You can plant 2x2 Saplings or even more of them together. Then a tree with a larger stem (4 blocks thick) might grow. Or maybe two trees on top of each other. The maximum size of player-grown Ashenwood trees seems to be 2x2 blocks in width, but maybe you'll be able to grow even larger trees?
You can use fertilizer (Pigsy Droppings) on Ashenwood Saplings to make trees grow 15 minutes faster (but you cannot fertilize "fallow" Saplings, since they won't grow no matter what). After that you'll just have to wait.
Trees you grow yourself usually will be of small height with a symmetrical shape. They might often not have any Flowers nor Beehives on them right away, however those can grow/spawn by themselves on any tree-top later on. "Home"-grown Ashenwood-trees might not always feature Moss, and this also cannot grow later.
It will take ca. 15-16 RL-hours until trees eventually "sprout" from Saplings - unless they are "fallow" of course. It does not matter if you are online or nearby. Saplings will turn into full-grown trees instantly which you can observe if you're close at that moment.
It is possible to make Ashenwood trees grow on other trees. It can even happen unintended when planting Saplings very close to each other. Also triple-trees or higher "staples" of trees can be grown deliberately by placing blocks of green Grass (or Dirt or Snow Cap) with Water (or Mineral Water) on tree-tops to plant your Ashenwood Sapling there.
If you put Ashenwood Saplings into Flower Pots, Wood Planters, on Wall Shelves, Hidden Temple Altars or Placemats, then the Saplings will not grow into trees there, but will merely be preserved and displayed for decoration.