This pine, P. elliottii has very long needles. It is in the same sub-genus as loblolly pine, and pitch pine, but has longer needles than both of them. Because of needle length, they will be difficult to make a convincing bonsai. But if you enjoy growing them, keeping them healthy is "good training" for working with better species for bonsai, such as Pitch pine, P. rigida, or even Loblolly pine, P. taeda. You could trim the needles to just 2 inches, doing so will always leave brown needle tips, but it will allow you to "see" how they would look styled as pine bonsai. Or you could leave them wild and bushy, the way they naturally grow. I like that P. ellioti develops corky bark on fairly young trees. This is an interesting trait.