If plants need air and water to thrive, it makes sense that plants would do well when watered with carbonated soda pop, right? Wrong, many garden and horticulture experts say, but there are other fizzy drinks that can benefit houseplants.
According to botanist David Hershey with madsci.org, plants quickly become dehydrated when they are watered with sodas like Coke or Pepsi. The reason, Hershey says, is the sugar content of these sodas, which changes the concentration of the soil and can make it hard for the plants to absorb water. Hershey also says that plants can’t absorb sugar since plants create their own sugars through photosynthesis. The sugar that the roots can’t absorb dries out the roots.
Plants watered with sugary sodas can also develop mold, according to Hershey, because sugars can stimulate rapid mold growth in soil. The microbes, Hershey says, harm the plant when they use up the soil’s oxygen and nutrients and produce waste that hurts the roots.
Gardenguides.com points out that even if soda pop itself doesn't kill the plant, insects might. Bugs like ants are attracted to sugar, while other pests might be attracted to the mold the sugars produce in the soil.
A fizzy drink that could help plants is seltzer water, according to gardenguides.com, which cites a 2002 study. The University of Colorado study found that plants watered with club soda grew quickly and enjoyed other benefits because there are more nutrients in club soda than in regular tap water. The National Gardening Association also cites in a reader’s forum that club soda is good for plants because the carbonation supplies them with boost of carbon dioxide.
According to Hershey, sugar-free soda pop would not be as bad for plants as regular soda, since these drinks use artificial sweeteners instead of sugar. But he did not name any benefits to using sugar-free soda versus ordinary water or club soda.