Lawn service companies often say in their advertisements that a well-maintained, average-sized lawn produces enough oxygen for a family of four. A popular political fact-checking website might rate this claim as “mostly false.”
It is true that if you count up all the oxygen molecules that an average-sized lawn puts into the air, that number is approximately equal to the oxygen needs of four humans (at least, if the four humans sit very still, and avoid engaging in any activity that might increase their oxygen demands). However, doing the math this way assumes that the system of interest includes a lawn, four humans, and nothing else.
The companies that promote this claim surely intend for the system to also include themselves and their services. In other words, they mean for it to include lawnmowers. And it turns out that the amount of oxygen produced by an average-sized lawn is somewhat less than the amount of oxygen that is consumed by the internal combustion engine of a lawnmower in the course of cutting that lawn.
So, a more realistic calculation finds that lawns result in a net loss of oxygen from the atmosphere.
Even if the claim were completely true, the savvy consumer would ask themselves how much oxygen is produced by lawn alternatives. A prairie planting or forest garden produces more oxygen than a lawn of the same size, while sacrificing less of that oxygen to motorized maintenance equipment. A homeowner who wants to be sure their family has enough air to breathe would be better off going with a natural yard than a lawn.
But in the end, it is somewhat strange to evaluate landscaping options on the basis of how much oxygen they produce, since our planet is not suffering from a shortage of oxygen. Running out of breathable air is not a problem we are going to face in the foreseeable future. If a company is trying to promote lawns by claiming that lawns solve a problem that does not exist, we should wonder why this company doesn’t have anything better to say about its product.