Hydroponics vs soil, all you wanted to know

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Hydroponics seeks to grow plants without soil. But is this any better? In this post, we are going to take a deep dive into the peer-reviewed literature comparing soil crops with hydroponic ones. We are going to look at papers that compare yields, quality, cost, and environmental impact. This will help us determine which growing method is better and under which circumstances. In this comparison, “hydroponics” encompasses any crop grown without soil, including those grown in soilless media.

Lettuce grown in a hydroponic and soil setup

How to compare

It can be hard to compare soilless and soil culture due to the many ways in which both can be done. Soil crops can be grown with or without fertilization, with or without irrigation restrictions, organically or with synthetic fertilizers, in a greenhouse or the field, etc. Different soils can also have widely different qualities and properties. Similarly, hydroponic crops use a wide variety of different systems and nutrient solutions. For this reason, I will focus my analysis on publications that try to directly compare products grown under both methods by the same researchers.

I will also look into literature reviews that try to describe the global picture. These articles can be important, as they can help us evaluate the impact of soil and soilless culture on a much larger scale. These can help us see the impact of all the different methods used and how tilting the scale one way might affect the big picture.

Quality

Many different studies have compared the quality of vegetables and fruits grown in hydroponic and soil cultures. The table below, shows you some of these studies and my assessment of the “winner” in each one, given their conclusions. I also analyzed these reviews on the matter (12, 13) that looked at the publications on the subject.

RefProductPropertyWinner
1Lamb LettuceShelf-lifesoil
1Lamb LettuceQualitysoil
2StrawberrySizehydro
3LettuceNutrient densityhydro
4SoybeanNutrient density hydro
5StrawberryNutrient densityhydro
6Strawberry Nutrient densityhydro
6RaspberryNutrient densitysoil
7StrawberryNutrient density & tastehydro
7RaspberryNutrient density & tastehydro
8Strawberry Nutrient densitysoil
9Strawberry Qualitysoil
10CucumberQuality hydro
11PepperAntioxidantshydro
12PumpkinQuality hydro
Different studies comparing soil and hydroponic crops

The above results show us that, while hydroponics can produce better or equal results compared with soil, it is by no means guaranteed to do so. If the conditions of the hydroponic system are not adequately controlled or the soil is of much higher quality, the hydroponic system might perform worse.

Neither soil nor hydroponic systems are a guarantee of better or worse quality. It is false to assert that soil crops – even those grown organically, as in some of the above studies – can always provide better results compared to a hydroponic crop. Nutrient density, freshness, taste, and quality can be just as good or even better in a hydroponic system.

However, because of the larger control that the grower exerts in a hydroponic system, it is probably easier, on average, for an inexperienced grower to deliver better results in soil. This is because soil culture is more forgiving, and takes care of more aspects that a grower would have to directly control in a hydroponic system, such as root zone chemical conditions.

Yield

I would suggest reading this blog post I wrote about hydroponic yields first. In it, I talk about the issue of yield in hydroponics, and how the most frequently cited yields per acre – which come from a couple of books that do not properly cite their sources – cannot be assumed to be reliable. To compare with soil, we should therefore look at publications that have done their own experiments to compare both types of culture.

Yield comparison for zucchini grown under a variety of different soilless media and soil. Taken from here.

From the articles I reviewed on the subject, none of them gave soil the upper hand. All articles showed an increase in yield in terms of product produced per plant or area, to hydroponic growing (14, 15, 16, 17, 18). However, it was notably difficult to find articles comparing soil and soilless growing methods directly in terms of yield (as you can see I only found 5). This is likely because it is widely assumed that hydroponic crops always give larger yields per acre, so few bother to study this difference directly.

The magnitude of the yield differences is also interesting. Although the books described in my post about “hydroponic yields” cite differences greater than two orders of magnitude, the studies show differences that are always lower than one order of magnitude and most of the time below a 2x increase in yields. This means that, while hydroponic crops are more productive per area, to expect yield increases of 10x when going from soil to soilless culture is unreasonable. Depending on the crop, increases of only 20-30% might be reasonable.

It is also important to understand that higher yields are associated with more complicated hydroponic setups. For this reason, the largest reported yield increases might only be accessible through much larger capital investments.

Environmental impact

The environmental impact of hydroponic crops depends largely on how they handle nutrient solutions (18, 25). Open hydroponic systems will have significantly more water and fertilizer usage than closed systems. In closed systems, the type of system and the efforts made to treat and reuse nutrient solutions will play a key role in determining environmental impact (19, 20). With this in mind, an open hydroponic system is highly undesirable in terms of environmental impact. However, if you treat the runoff (22), this would be desirable over a soil system that uses synthetic fertilizers.

Note that the environmental impact of hydroponic systems increases dramatically if it uses artificial lights. If this is the case, a soil-based approach will always have a lower impact, unless renewable sources are used to produce the energy.

In the case of soil, environmental impact can be very different depending on the growing practices used. Organic growing approaches will deliver significantly lower impact compared to traditional soil agriculture, mainly due to the lower energy expenditure and because they avoid contamination of soil and aquifers with large amounts of nitrates and phosphates (21).

When considering environmental impact, it is also important to consider yields per area. While a closed hydroponic crop might have a higher environmental impact per acre of land used than an organic soil crop, if it produces 3x more product, the environmental impact per gram of fruit or vegetable produced might be much lower. Although I couldn’t find any direct studies comparing the environmental impact of soil and hydroponic approaches, it would be reasonable to think that a closed hydroponic system should have a lower environmental impact per gram of product, as long as the yields per area are significantly higher compared to the organic soil approach.

With that said, an approach that makes use of low energy inputs makes very efficient use of water, and has a high planting density, might be the ideal growing system in terms of environmental impact. I suggest you read my blog post about aquaponics if you’re interested in this topic. Closed hydroponic systems that use treated sewage instead of newly prepared hydroponic nutrients might also be extremely low-impact, high-productivity systems (22, 26).

Cost

Money is important in agriculture, as it is often the main driver when determining the growing system. Hydroponic crops have higher startup costs compared with soil. This is because the minimal hydroponic setup is substantially more complex relative to the minimal soil setup. However, even when greenhouses are involved, the hydroponic setups will often have higher starting costs (23).

Although starting costs are higher, life cycle costs of hydroponic setups can be lower due to higher yields, fertilizer, and water use efficiency. This is especially the case when you grow highly efficient crops, like lettuce. In this study, (24) they compared the yield, cost, and water efficiency of different hydroponic and protected soil setups. Hydroponic NFT setups were much more water-efficient and much more feasible from an economic perspective.

Hydroponic crops also have access to areas that are traditionally unavailable for soil agriculture. For example, hydroponic crops can be grown on rooftops and produce significantly more money than solar panels under some conditions (25). In this case, hydroponic crops fill a niche that has no soil-based equivalent, since the area would never be used by soil agriculture.

Conclusion

The best soil grower is better than the worst hydroponic grower. The best hydroponic grower is better than the worst soil grower. The most important thing when you decide to grow a certain way, is to strive to do it in a manner that leads to higher quality, that maximizes yields, minimizes environmental impact and, if possible, is done at a low cost.

Soil agriculture has its place. It is cheaper to start with, requires fewer materials, can be done at a much larger scale, and can produce high-quality, sustainable results when done correctly. Hydroponic culture offers higher yields per area, potentially lower environmental impact, and lower life cycle costs. However, it costs more and requires substantially more knowledge and care to provide comparable results.

Have you grown in soil and hydroponics? Which one do you like best? Let us know in the comments below!

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3 Comments

  • John McGee III
    April 19, 2021 @ 12:06 pm

    I have grown small gardens with several kinds vegetables most of my life and i was born in 1953. Late last year I began switching to floating hydroponics. I live in west central Florida and the hydroponic boxes are located outside. I now have two 4 X 8 feet boxes with holes on 6″ centers.
    Her is what I have found:
    Due to poor soil conditions in my part of Florida start up cost are about the same due to have to having to heavily amend the soil.
    Far less nutrients are used as you can test mixture yourself. (no lab cost)
    Much less water used, none wasted.
    No bug problems that are inherent to soil. Do not have to rotate crops.
    Multiple vegetable types in much smaller area, i.e. squash, cucumbers, tomatoes, beans, peppers, eggplants, cantaloupe, and spring onions, okra, strawberries.
    Also growing cotton and peanuts all of these are in one 4 X 8 foot box.

    I am now a big fan of floating hydroponics. I know there may be some issues that come up in the future but i have encountered so many with soil I almost stopped growing anything. Open a new are to experiment with.
    J

    • admin
      April 19, 2021 @ 12:51 pm

      Thanks a lot for your comment! I appreciate you sharing your experience with us. I have had a similar experience, when you’re living in a place with “bad soil” hydroponics are the easiest way to go. Organic soil gardening can help fix the soil and make it more arable, but does require much more effort.

  • Sam
    April 25, 2021 @ 7:32 am

    It seems odd to me to make comparisons between different growing methods using a “nutritious” criterion. There are many dozens of naturally occurring chemicals in any food, and so which ones do you choose in the comparisons? I’m sure simplifications are made, but since we don’t know how all those chemicals affect our bodies, such comparisons may be only arbitrary guesses.

    The same with “taste.” There are self appointed authorities regarding taste, as for example in wine tasting, but such a subjective thing again can only be arbitrary.

    Our oceans contain natural hydroponic systems, with the “crop” being seaweed. I understand that seaweed farms in open ocean waters is of increasing importance because the food yields per acre are much more than on land. Even with regard to biomass for energy source. I doubt very much that sea farmers would ever succeed in artificially synthesizing their growing medium, if they would ever seriously attempt it.

    Are there any hydroponic fresh water systems on land? My guess is no because all the fresh water plants I’ve seen are rooted in soil. Perhaps that means that it’s not possible for fresh water to contain enough nutrients for natural plants? It thus appears to me that hydroponic farming is a uniquely human invention, perhaps suggesting that hydroponics truly something that nature abhors?

    How many different chemicals are tracked and maintained in closed system hydroponic farming? Judging by agribusiness, it can’t be very many. With agribusiness, the soil insures the farmer that there are enough nutrients available for the plants, beyond what the farmer adds. Thus, land farmers can be as ignorant as they are and the land will still provide, albeit the products leave much to be desired. There is no way agribusiness can provide the quality of food we produce in our backyard organic garden. It’s very sad to me to know that generations of humans are raised who never experience what a really good apple is, for one example This is true for most any other fruit or vegetable. It’s also true with meats. I know the luscious taste of naturally raised chicken, pig or cattle, and I experience it now and then during trips to small villages in the Philippines.

    And it’s not a question of “organic” farming. It’s bigness. I’ve given up on the fruits now available at my local organic market. They are just as tasteless as the ones from the supermarket. And they look just as “perfect.”

    For all these reasons, the large numbers of chemicals and nutrients and our ignorance on what they all mean, and the threat of “bigness,” I’m a bit distrustful of hydroponic farming. I suppose it can supply niche markets and people will buy into them, but it may be that this role can only be a fringe role. If hydroponics becomes a major source of food, for people or animals, in my view, it will only be one more folly invented by humans in our march to destroy the planetary ecosystems that make our lives possible.

    I acknowledge that I’m largely ignorant about hydroponics, and the subject has always been a puzzle to me. Why? Are the intentions behind it to help us survive as a refuge in the planetary ecosystem we are destroying? Are there unique products that land farming cannot provide?

    I understand that people will do anything feasible to earn a living, and then find intense interest in doing it. But is there a fundamental driving force, as there is with land farming or fishing, or do people do it for myriad, more superficial reasons?

    Thank you for your blog and articles, which I find very interesting, and I’m sure you’ve had many discussions with others regarding the issues I raise.

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