I bought some plum trees. Can I plant them now?
This may depend on your growing zone. Is the tree leaved out or a bare root? Bare roots are dormant and can be planted out sooner in spring then a leaved out potted tree. If the tree is leaved out and you live in a cold climate with risk of freezing temperatures you will need to wait until danger of frost has passed.
Generally spring or fall are best times for new plantings, but with proper care you can plant anytime.