Why Aren't Gardens the Best Way to Capture Carbon Dioxide?

I find this an interesting topic and I am not by any means discouraging people from gardening. There are numerous reported health benefits ranging from decreased stress to increased happiness and longevity. Gardening is very rewarding and I am frequently upscaling my stock of plants so that I can actually make a difference. But what I want to discuss is the side of it that is never covered because it’s very disheartening. In most cases, planting your small garden doesn’t decrease your carbon footprint.

So why would I say such a terrible thing? Of course planting plants should lead to decreased CO2 and an increase of improved air quality. Of course plants have numerous benefits even outside of this to include shade, transpiration, nutrient retention, erosion control, medicine, and food. But what is never discussed is the chemistry behind this. We always stop at photosynthesis and don’t look past it.

There’s this concept of conservation of mass (might have seen it written as conservation of mass-energy). Matter doesn’t get created nor destroyed; it changes forms. The CO2 the plant used to make glucose has many fates. Some is converted into other simple sugars such as fructose, ribose, and galactose. Some of these are combined into larger saccharides such as sucrose, cellulose, and starch. And some of this can be converted into amino acids and proteins, nucleotides and DNA, and lipids and triglycerides. This is where the CO2 is going after the plants absorb it.

So, great. We all knew this or at least we knew the plants were putting it to use but then what? Plant cells also need energy so they burn their own sugar and this produces CO2. So some of it does leave the plant but this is less that what they take in, otherwise plants would starve and die (which does happen, usually as a factor of warm nights, lack of water/CO2, and low light conditions). But what about the rest? Once the plant dies, bacteria, fungi, and animals process most of it back into CO2. In the case of humans, we can’t digest the cell walls which is why we call plants a great source of fiber. But even then, bacteria/fungi eventually get to it. And not all of this goes as CO2, some will leave as carbonates, and some will become hydrocarbons which we find underground as oil, coal, and natural gas.

So this raises questions. How do we remove the CO2? We have been digging/pumping it up and burning it while also clearing land and burning trees. Even if we replanted these trees, we still have plenty of extra CO2 floating around.

An interesting hypothesis is to grow fast growing trees/bamboo and to bury the dried plants. This could remove several tons of CO2 a year and reverse global warming much faster than the natural absorption by land and water alone. Although faster, this would probably still take decades.

We could switch to alternative energy. Biofuels are my favorite. These are “carbon neutral.” This means we remove the CO2 from the air (often with plants/algae), process it, and burn it. This completes the cycle. Other alternative energies are also hopeful but tend to be quite polluting when in production. Nuclear shows the best statistics at the moment for power output per ton of pollution but isn’t very viable for vehicles unless they are electric.

We could drastically reduce luxuries too but that won’t take off.

We could replant trees. Trees are loaded with plant fibers and will live many decades. This means a large quantity of CO2 is being held onto this whole time. Now cut millions of these down and replace with small plants like grasses, beans, or corn, or leave the soil bare like we see commonly happen. Either way, the amount of plant fiber in this given area has drastically dropped. Where did that carbon go? Undoubtedly, much of it is back in the air while the rest of it is settling into the earth. Small farms aren’t much of a problem but you can see how this can scale up with area. So planting a lot of trees will help negate the damage we’ve done. But this goes back into the problem we had before, if we replace all the trees we’ve cut down, we still have billions of tons of carbon we pulled up from the ground that is circulating around.

As you can see, this isn’t a simple problem and there is no one solution to this. We would need to combine ideas and even then it could still take decades to see improvement. At current conditions, the half-life of CO2 in the atmosphere is about 100 years. If we can manipulate our environment to absorb more CO2, we might be able to fix this. But unfortunately, a small garden wouldn’t do much to sequester anything.

By all means, continue your gardening. The more plant matter you can add, the better you are doing. Grow much of your own food to cut down on fuel consumption. Donate plants to spread happiness. Plant ornamental plants to collect various pollutants out of the air. Plant trees. It all helps. But don’t listen to the reports that say your house plant removes hundreds of pounds of CO2 from the air each year. It puts most of it back into the atmosphere. These are for hype and they make us seriously underestimate the problem. A few houseplants have very little contribution. If we are to truly make an impact, we need to not only plant, but we also need to reduce our consumption and find new ways to remove CO2 from our air.