From my understanding it is best to have soil with good drainage to overwinter your trees. I live in zone 5b so it gets really cold here. I have several trees that I've gotten from nurseries that are in black soil and a couple of baldies in muck. Im somewhat concerned about the amount of water they hold. Its obviously to late in the year to get them in proper bonsai soil. Does anyone have any recommendations? I was wondering if it would be beneficial to poke some small diameter holes in the soil to help improve drainage a little bit? Any suggestions or advice would be appreciated.