I hope to visit the Trsteno Arboretum from Dubrovnik this coming May. I'm having trouble finding information about the hours during which it is open, so if any of you know, I'd love to hear from you. Also, my understanding is that I can get there by taking one of the buses that head northwest from Dubrovnik (for example, to Split), and that I can flag down one of the southeast-bound buses to Dubrovnik when I am ready to return. Is that correct?

Any information you can provide will be much appreciated.

I would email the Dubrovnik tourism office, as it seems none of our resident Croatia-philes have visited the place.
Also, if you are unable to make it, you may enjoy the much smaller botanical garden on Lokrum island.

The bus from Dubrovnik to Split will drop you off right in the town of Trsteno. The hours during May should be 0800 to 1500, daily.

Enjoy the gardens, they are really spectacular.

Trsteno is lovely. Aside from the botany, the views are gorgeous (but gorgeous views a are a dime a dozen in Southern Dalmatia). Also, a bit to the south of the gardens all the way down by the sea is a fabulous ruin of a villa right on a little marina where you can swim and explore. It's a very romantic spot.

Also, Yorkshire's suggestion of visiting Lokrum is EXCELLENT. it's just a short water taxi ride from Dubrovnik Old Harbor and is fantastic. You can spend a very relaxing and enjoyable half day on this uninhabited island. There is a cool cafe and lounges under pine trees.

Emjoy.

Thank you so much! This information is very helpful.

I definitely plan to go to Lokrum - I really want to see Dubrovnik from the sea! I am also hoping to have some time to spend on the island, but I know I won't have time to see everything I want to see in the area. Perhaps you can help me with that, too - do any of you know when the last ferry/water taxi from Lokrum back to Dubrovnik runs in late May?

The small boat to Lokrum is up and running, everyday. They will vary the return hours as daylight gets longer. As of today, it goes from 7am to 7pm, that could change tomorrow. You can stay on Lokrum as long as you desire, but can't miss the last boat.
Dobrodosli u Dubrovnik

Again, my thanks!