This small fabric mod allows you to place vegetation on almost all blocks.
Download .jar file from https://www.curseforge.com/minecraft/mc-mods/placeable
Put the file in mod folder
When you right click on a floor block, with some plant it'll be plants
The available plants are:
- Deadbrush
- Fern
- Flowers
- Grass
- Saplings
- Bamboo
- Cocoa beens
- Crops