I have three magnolia trees in pots. They were bought as small plants earlier this year. I wanted to know whether I should put them in my unheated greenhouse over winter or just leave them outside? I have one in the garden but the others are in pots. Thank you for your help
Do you know the variety of Magnolia Tree that you have purchased?
Most Magnolia are hardy to zones 7 through 9.
The Star Magnolia is hardy down to zone 5.
If you are unsure of the variety you certainly should move them to a sheltered location and provide some extra insulation around the pot.
Adding some mulch to the soil surface also will help.
Here are some links with more information.