Your six needles aren't true needles. When they open like this in spring, it's time to cut off the roots and prepare them as cuttings. The next growth will show the true needle properties of your trees. I suggest feeding just a smidge and keeping them in a cool greenhouse this winter. Of course, well-established one year old plugs will survive freezing at the rate of 100%. But yours are a little too young, so keep them above freezing and begin working with them in spring.
Here's a link that you might find helpful.
Japanese black pine from seedlings