That is an interesting little pine...be patient and get it established...then you should be able to do almost anything with it!!
I have always thought that P. virginiana would make decent bonsai with its short needles and decent bark. However, I was never able to successfully collect any that had any age to them at all. Frustrating...ground to pot a real challenge!
I finally located some small seedlings and asked permission to collect them from a neighbors front yard. No problem, collected 50 6"-12" seedlings and put them directly into a grow bed. About 10 died, but the rest survived and thrived! For the next year I just let them grow. One mistake I made was planting too close together...they were fine in the beginning but as they got to 3-4' tall they were much too close together. I pruned hard in June of the second season and all trees responded with vigorous back budding and regrowth...so I pruned hard again in late July and was reward with even more budding and regrowth...needless to say this can be a very vigorous species when grown in the ground. Things are looking good but is the real challenge going to be moving them to a pot??
In early Spring of the 3rd season it was time to thin the growing bed and move a few into pots. I choose about a dozen to dig and move into nursery containers. I neglected to mention that I had removed the taproots when I originally planted the seedlings...this was good...the trees came out with nice lateral roots and I was hopeful that they would transition well to pots... Unfortunately I lost all but 4... My best estimation was that I was too early...it seemed to take too long before the trees started to grow. They were also difficult to stabilize in the containers and it is possible that the high winds of Spring didn't do the new roots tips any favors. The good news is that I now have 4 doing well in anderson flats.
The next Spring I waited a till mid spring and tried again...same results...a 3 out of 10 survived.
The following year I waited until the trees were actively growing...late spring/early summer...success was only marginally better.
Ultimately out of 40 seedlings, I have 9 or 10 P. virginiana in containers now...one note, I discarded about 25% trees due to a total lack of potential from growing too close together
What I think I have learned thus far...
1. very vigorous growers and can easily have all new growth removed 2-3 times a year when in the ground...twice in a container.
2. needles reduce well but maintain the twist...so far I am not sure this will ever make a "well-manicured" bonsai...but it might with time.
3. very tough to transition from ground to pot culture!!!! But, once in the pot it seems to do just fine. Be sure to secure the tree well in its container.
4. Bark development is slow...faster growing trees seem to develop sooner...my largest tree has the most developed bark...
5. Very susceptible to tip moth but the end result is just more buds
6. And the real kicker that I am sure will raise a stink...is that I have had a zero survival rate in bonsai soil...the only trees I had make it were/are in a quality potting soil...eeek!!!
I definitely think this is a species that more people should be working with!!
Here are a couple pics of a group(3 of the first 4 survivors) I put together to resemble the tall pines that we have here in the Southeast. This is just after wiring, pruning and needle cutting this past May.
I have also been playing with about 50 Coastal Loblollys...perhaps more to come in the future on these but it is still early.
John