In the second potting of collected material I sometimes use Polystyrene chips in the bottom of the growing on pot. It has three key benefits… In winter the pot stays warmer longer, the roots have free run to grow rapidly and re-potting is a lot easier..and cleaner.

This Taxus has been three years in a feed bucket, it was root trimmed and put back in the same Bucket with new soil and Polystyrene chips in the bottom… as much more growth on the top is required.

I use this technique on Taxus, Prunus and Crateagus. I would NOT recommend Pine and Spruce.