Vegetation is grown there, presumably hydroponically. The purpose of the Botanical Gardens is presumably to help create oxygen for the human crew to breathe (although the ship also has Oxy-Generation Units for this), and also presumably to grow food. It also likely doubles as a park, for the leisure and recreation of the crew. (Infinity Welcomes Careful Drivers novel)
Although not seen in the television series, the Botanical Gardens have nonetheless been mentioned numerous times in the show.
The Botanical Gardens featured prominently in the first issue of the Red Dwarf Smegazine. This remains, to-date, the only time the Botanical Gardens of Red Dwarf have been visually depicted in the franchise.
In the comics, the gardens are depicted as bizarre and alien-looking (likely genetically-engineered) trees and plants, contained within massive, hermetically-sealed domes. These domes are likely forms of bio-domes (such as Biosphere 2 or the Eden Project), or perhaps research vivariums.
Some of these plexiglass domes are clear, whilst others are tinted red or orange, and some are obscured completely. The domes come in all different shapes and sizes; with some being larger than a football field, and others being no larger than a greenhouse. The larger domes rest on the floor of the deck, whilst some of the smaller domes are suspended on high by poles.
It is unknown what the Botanical Gardens looked like, at least in the continuity of the television series.
Red Dwarf's botanical gardens were presumably similar to ones seen aboard other ships, such as Justice World, where they appeared as dense, green vegetation in glass domes on the outside ("Justice", Series IV), and on the inside appear completely similar to an outdoor park in London back on Earth. ("Justice" deleted scenes)
Mentions in the television series
Whilst working Z Shift, and after unblocking a chicken soup dispenser, Arnold Rimmer and Dave Lister (during their first appearance) were sent to the botanical gardens on a job once to repair a faulty "porous circuit". ("The End", Series I).
The botanical gardens were host not only the flora, but also some resident fauna. Sometime before the radiation leak, but after being dumped by Kochanski, Lister went down to the botanical gardens to be alone with his thoughts. Feeling depressed, Lister saw a squirrel climbing up one of trees, and wished he could be the squirrel - without a care in the world. Three million years later, Lister recalled his thoughts on the squirrel to much mocking by Rimmer and the Cat, and Rimmer says that Lister is a "closet squirrel". ("D.N.A.", Series IV)
In the final episode of Series X, the Boys from the Dwarf are repeatedly tracked down and harassed by a bored and non-threatening Simulant named Hogey the Roguey, who frequently challenges them to "duels across time and space" to relieve the boredom of being stuck in Deep Space. Rimmer suggests that they have a ping-pong marathon, whilst Lister suggests that they play crazy golf in the botanical gardens, giving Hogey "a shot a hole". Hogey refuses since Lister knows the botanical gardens too well and will inevitably win. ("The Beginning", Series X)
- It is possible that the Felis sapiens that evolved on Red Dwarf over three million years may have survived, in part, due to eating food grown in the botanical gardens.
- The Rimmer family home, located in a colony on Io, had botanical gardens. These were maintained by Dungo Dennis, actually Arnold Rimmer's biological father.