I have no experience with a greenhouse, but I have brought plants and/or cuttings into the house for winter. I wash them with soapy water before bringing in . I also use a systemic killer on at least some of the plants as I think it helps to break the cycle of exploding populations of bugs. Any bug killed by eating the treated plants can't have babies... So if you can't treat all the plants with a systemic, but do some of them, I think it helps in controlling them.
Karen
