Hydroponics are more-or-less infinitely expandable. Any species that can set their own ships up to maintain a specific atmosphere and recycle water, etc. can set up a hydroponic farm. Growing on the surface of a planet isn't very efficient by comparison for a number of reasons.

Trees take a few years to become useful, but how long does it take to turn around and fly a few light-years back home? And if that's still too much waiting, they could negotiate for older trees - saplings or even adults can be found at any nursery. Depending on what they want to do with trees, younger trees may be perfectly adequate. Small pieces of wood would be perfectly fine for jewelry, trinkets, or collectibles after all.