Many Decorative Items cannot be deleted until they have been fully constructed. If items never seem to be completed, you may not have the materials required. For example, if you want to place an Apricot Tree, you must have at least 5 Apricots and 5 Logs in storage.
Not all Decorative Items can be removed using the Removal Tool.
If you click on the item, there may be a ""+"" sign or a trash can in the window. If you don't see either, you should be able to remove the item using the standard Remove Structures Tool.
If there is a trash can, click on it to remove the item.
If there is a + sign, click on it to make the item impassible. After it is destroyed and rebuilt, use the regular Remove Structures tool to remove it.