What Plant Produces the Most Oxygen?

Quick answer: Earth's biggest oxygen makers aren't for sale at a garden center. Around half of the planet's oxygen is produced in the ocean, mostly by plankton, and on land the leaders are big, healthy, fast-growing trees. Indoors, the winner is simply whichever of your plants is biggest, healthiest and putting on new growth in good light, and even it supplies only a sliver of what one person breathes.

Below we walk through each scale, clear up two popular myths and look at what genuinely freshens the air in your home.

Oxygen Comes From Growth

In photosynthesis, a plant uses light to build sugar from carbon dioxide and water, giving off oxygen as it goes. At the same time, it respires day and night, burning part of that sugar and consuming oxygen. Its yearly contribution to the air is whatever is left over.

That leftover is visible as growth. When a plant puts on weight, it has stored carbon, and each 12 pounds of stored carbon means roughly 32 pounds of oxygen released. So the plant that makes the most oxygen is the one adding the most new tissue. A plant that has stopped growing contributes next to nothing.

The Ocean Does Half the Work

According to scientific estimates, roughly 50 percent of the oxygen made on Earth comes from the ocean. Most of it is made by plankton, tiny drifting plants, algae and photosynthetic bacteria. Sea life consumes about as much as it makes. Photosynthesis on land supplies the other half.

No one forest keeps the world breathing, either. Oxygen makes up about 21 percent of the air, a reserve so huge that burning all fossil fuel reserves, all trees and all soil organic matter would lower it only slightly, by a few percent. Trees are worth planting for storing carbon, removing pollution and cooling the air, but nobody is running out of oxygen.

Big Trees Win on Land

Outdoors, size and growth rate decide it. Research on urban trees across 16 cities in the United States and Canada found net oxygen output rising sharply with trunk diameter, measured at chest height. These figures come from a single city in that work.

A typical adult breathes in about 1.85 pounds of oxygen daily, close to 675 pounds over a year. The same research found it takes about 30 city trees on average to supply one adult, ranging from 17 to 81 depending on size, health and growth. A full acre of tree canopy supplied about eight people, under half the commonly repeated figure of 18. And a tree that is dying or rotting reverses the math, using up oxygen as it decays.

Where Houseplants Fit In

Even a young street tree whose trunk measures 1 to 3 inches nets roughly 6 pounds yearly, less than one percent of an adult's needs. A potted plant indoors gets much less light and grows much less, so it makes even less. You would need hundreds to cover one person.

Light is the limit. Outdoor sun can hit 10,000 to 12,000 foot-candles, and even a bright spot by a sunny window gets a small fraction of that, with levels falling fast a few steps from the glass. A plant in a dark corner hardly grows, so it adds almost no oxygen.

Your best oxygen plant, then, is the biggest, leafiest one pushing out new growth in strong light. In dim rooms, tropical foliage plants that tolerate shade cope best. Our houseplant care guide and our page on indoor grow lights for plants explain how to keep one growing. Just grow it for the pleasure of it rather than the oxygen.

What Plants Do at Night

Plants Do Release Carbon Dioxide

Every living plant respires, giving off carbon dioxide around the clock. In good light, photosynthesis absorbs more than respiration releases, and that surplus becomes growth. In the dark, most plants release a little carbon dioxide.

In one test, five common foliage plants sat in sealed chambers through 12 hours of darkness. Carbon dioxide went up with dieffenbachia, lucky bamboo and ZZ plant, and went down with snake plant and Cryptanthus. Overnight, a plant's respiration is tiny compared with a sleeping person's, so a few plants won't use up the oxygen in a bedroom.

The Snake Plant Myth

Snake plant (Dracaena trifasciata, once called Sansevieria trifasciata) gets more credit than any other houseplant for making oxygen at night. What it really does after dark is absorb carbon dioxide. Like cacti, it runs a water-saving version of photosynthesis known as crassulacean acid metabolism (CAM). The pores on its leaves open at night, when less water is lost, and it stores the carbon dioxide it takes in as an acid.

The step that releases oxygen still requires light. By day the pores stay shut, the plant breaks down the stored acid, releasing carbon dioxide within its own leaf tissue, and turns it into sugar using light. That is when the oxygen comes out. So a snake plant takes in a little carbon dioxide overnight, but it isn't pumping oxygen into your bedroom at night.

What the 1989 NASA Study Found

The idea that houseplants clean the air goes back to a NASA report released in September 1989 together with a landscape industry trade group. Researchers put single plants in sealed Plexiglas chambers, the smaller ones roughly 30 inches per side, added benzene, trichloroethylene or formaldehyde, and measured what remained after 24 hours.

Many plants did reduce the chemicals in those boxes. But the first year's tests used 15 to 20 parts per million, a level the report described as far above anything found indoors. The second year dropped below 1 part per million, but the chambers were still small and sealed. In one round, a plant-free pot of soil took out roughly 20 percent of the benzene, and the authors concluded the root and soil zone seemed to do the most work. The summary also recommended pairing plants with fan-driven activated carbon filters.

The study never measured oxygen output and never tested a normal house with ordinary air exchange. Snake plant was among the plants tested, listed as mother-in-law's tongue.

The Numbers for a Real Room

A 2019 review revisited 12 chamber studies with 196 results and expressed them as a clean air delivery rate, the figure air purifiers are rated by. For the median plant, that came to about 0.023 cubic meters an hour, less than one cubic foot. Typical buildings already swap their air with outside air about once an hour. Matching that with plants would take 10 to 1,000 of them for every square meter of floor, or about 1 to 93 per square foot. In a bedroom of 150 square feet, that is about 140 to 14,000 plants.

The EPA notes that no evidence shows a sensible number of houseplants clearing meaningful amounts of pollution from homes or offices, and soggy potting soil can encourage microorganisms that trouble allergy sufferers.

Better Ways to Freshen Indoor Air

1. Tackle the source. Removing or cutting back whatever pollutes the air is usually the most effective step.
2. Bring in outside air. In fair weather, open up windows and doors. Attic and window fans help, as do kitchen and bath fans ducted to the outside. Give rooms extra airflow during painting or cooking. A typical household furnace or central AC doesn't mechanically draw in outdoor air, so switching on the system fan doesn't count as ventilating.
3. Filter particles. A portable air cleaner depends on both its filter and how much air it moves (its CFM rating), and most tabletop units do much less. Air cleaners generally aren't built to remove gases. Keep your furnace or AC filter clean as well.
4. Test for radon. You can't see or smell it, so testing is the only way to find out how much is in your home.

The EPA's page on improving indoor air quality covers each of these in more detail.

Common Questions

Which Houseplant Makes the Most Oxygen?

The biggest, healthiest one growing actively in strong light. Even a large plant covers only a small share of one person's needs.

Can Houseplants Reduce Indoor Carbon Dioxide?

Only a little, and only in good light. Outdoor air from an open window or a vented fan does far more.

Did NASA Prove Snake Plants Purify a Room?

No. The study measured chemical removal in small sealed chambers, and those results don't carry over to a ventilated home.