how do plants excrete
Plants use a variety of techniques to remove waste materials. Oxygen, a by-product of photosynthesis is removed through stomata. The excess water absorbed from roots is also lost through stomata via transpiration. Cell vacuoles, gum, resin etc. are stored in old xylem tissues. Waste products may be stored in leaves that fall. Plant roots also sometimes excrete wastes materials.
Hope this helps,
As plants produce their own food, things are a little different in plants than in heterotrophs.
However there are waste products from photosyntheis (its the opposite reaction of respiration eg carbon dioxide + water (and sunlight energy) --> glucose + oxygen. Respiration is glucose + oxygen -> carbon dioxide + water (and ATP energy))...these wastes in plants are gaseous and pass out the stomata in the same way carbon dioxide enters it.
Plants do also respire, but this is generally done at night, and both carbon dioxide and water are again gaseous and pass out stomata...