Winter, crabapple bonsai

Here is an update on my crabapple bonsai. Collected from the side of the road in Kentucky, it's now been four years in a pot. I am happy with the way it is growing, however I believe it's now time to put back into the ground for thickening. I will still keep the top cut back but what I hope to achieve is some thickening of the lower branches and overall improvement of the nebari. I hope to let it grow in the ground this way for about three to five years. I will attempt to update with a picture of it in the ground if I can get a good one.