Even decorative gardens come in all kinds of styles. The English garden reflects the value of pastoral life. Japanese gardens try to look utterly like nature but rely on extreme control for the maintenance of this appearance. French formal gardens have yet a different style. Gardens reflect culture, money, and the relationship of people to nature. There are also water gardens, greenhouses, and special gardens like the Orangerie in France, which was designed with walls to provide frost protection for citrus trees.
Gardens say a lot about class. Do you have a gardener? Or do you garden yourself? What kind of things do you grow? Are those things for show, for eating, for sale? Are they for medicine, as with the herb gardens possessed by monasteries and convents? Some specialized gardens are for cacti, or for poisonous plants. Morgan has written a story in which a main character identifies the doctor's house in the village by noticing the herb garden outside.
What about lawns? What makes them so appealing? People use them for sports. They are incredibly popular but also very water-intensive, and in California's recent drought many people moved toward xeriscaping, or intentionally designing a garden for very low water.
The location of a garden, and the climate in which it is being maintained, influence the content of the garden. For foreign plants, special steps may need to be taken. Foreign plants may become invasive because they don't fit into the local ecosystem, as with bamboo and kudzu - but they also tend not to have the same pests that a native plant would.
Soil quality varies a lot. So does the amount of labor required for land cultivation.
Gardens and plants can be very important for symbolism in a story. Dune by Frank Herbert used palm trees to show the wealth and wastefulness of the Harkonnen family. Nausicaa of the Valley of the Wind used the contrast between Nausicaa's indoor fungal garden and the outer toxic jungle to great effect. Gardens (like hers) can be used for science. In fact, a great deal of science has come out of our own gardens, such as Mendelian genetics. There is also grafting in fruit trees and roses.
Who are gardens intended to feed? Some people have grafted fruit tree branches onto public trees in order to feed the homeless. Sometimes, however, people are hassled for growing food instead of display plants, especially in front gardens. Nowadays we see more and more rooftop gardens. Hydroponic gardens are a favorite in science fiction, as are tower gardens. A museum in Paris has a garden that is its entire front wall.
Gardens on a spaceship are for oxygen as well as food. Alaya Dawn Johnson's The Summer Prince used algae gardens to great effect.
Where is the sun? The direction and quantity of sunlight is critical for a garden's success. In my own garden I had to move a huckleberry plant that was frying in the sun to a shadier location and plant it with peat moss to improve its health.
In The Martian, the protagonist grows potatoes on Mars fertilized with "people poop from space toilets."
A garden can mean different things in different contexts. My own house has a very large garden, but new homes in the area are getting much less land space. When I lived in Tokyo, the apartment I lived in had a garden that was advertised as part of its appeal, and it was a 4'x6' space with tiny hedges. At my homestay house a year earlier, in Kyoto, they had a back garden and also a tiny garden in an interior courtyard of the house, too small to walk into. Different cultures do different things with interior versus exterior gardens. Windows can be designed to frame the garden.
In my own fictional world of Varin, the people live in cities underground, but rich people can import soil and plants will grow in the light of the atmospheric lamps that provide daylight. They also use rock gardens. Where there are openings to the surface, they have agricultural towers to maximize the production with the limited light available. The city level just under the surface also has water gardens. Surface farming can only happen in small "islands" because clearing farmland is not possible.
Terraced fields are common in places where there are steep slopes, including South America and Southeast Asia, for example.
Will agricultural robots come to replace farm workers? Will bee robots help with pollination?
Plant life cycles and seasonal cycles influence what happens in a garden. People can design gardens to attract bees or butterflies or hummingbirds, or other creatures. They can also design gardens to resist the grazing of particular species like deer. Weeds have been fought for a long time, but what counts as a weed is different depending on context.
Thanks to everyone who joined us for sharing their thoughts!