Kingston W.
Yelp
If you are travelling by private vehicle, Byodo-In Temple is 15 minutes away. If you visit the gardens, I would include the temple as part of your day trip.
Ho'omaluhia Botanical Gardens is first, and foremost, a flood control project. It was designed, built and is maintained by the US Army Corp of Engineers.
I mention this because you will occasionally see signs asking you to stay out of, or refrain from taking photos in, certain areas. (I'm just saying).
The rainforest garden has plants from major tropical regions around the world. It also has a lake and walking trail.
From the visitor center towards the lake, the trail has a downhill grade. The first third of the trail is a serpentine concrete walkway. Afterwards, the trail is hardpack soil + aggregate mix. I would rate the walk as "easy" for most people who do not have mobility issues.
Towards the lake, there is a pavilion with picnic tables. There are a fewer picnic tables and benches near the lake.
The lake has a lot of koi.
Frankly, if you are looking for a botanic garden which curates and labels a lot of individual plant specimens, there are other botanic gardens on the island that do a better job.
However, this garden does provide a nice park experience; and the ambiance of a tropical paradise. (And this is first, and foremost, a flood control project.)