I have a weeping crabapple that was planted 12 years ago. It looks healthy but seems stunted in growth, so I think there is overcrowding in the area it was planted. Is it difficult to transplant this tree and will it harm it? If not, when is the best time of year to transplant?
It is very difficult and risky to transplant a 12 year old tree without professional tree moving skills and equipment. Have a consulting arborist or tree service assess the situation to determine if it is feasible.
If the crowding is from larger trees, then you have a problem. If it is from smaller plantings, consider moving those and not the tree.
The other option is to provide enough water and fertilization to accommodate the growth of all the plantings in the area.