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What elements does a plant need to grow? (github.com/hydromisc)
339 points by lathyrus_long 64 days ago | hide | past | favorite | 101 comments

I've been growing hydroponically through the pandemic. I'm now switching from commercial pre-blended nutrients to my own design, customized for my hard water and blended from individual salts. In the linked article, I briefly review the biochemistry, show the fertilizer design calculations using an open-source tool that I wrote, and review a lab analysis of the final solution.

This is a fair amount of work, and I'd guess that relatively few non-professional growers would bother. I hope this may be interesting to anyone generally curious about plant nutrition though, or about the design of modern complete chemical fertilizers.

Impressive work! I had a couple of questions.

- How do you find the best concentration for each nutrients for a given plant? I usually just make general-purpose mix with General Hydro but I see that your calculator includes some presets for specific plants.

- I see that your board includes pH and EC probes. I always wanted those in my setup but I've read that they tend to degrade fast. In your experience is that true?

- Where did you get the potassium nitrate? I always wanted to make my own mix but I've heard that buying large amounts online will put you on a list as it's a strong oxidizer (you can make explosives with it).

Not OP, but I can give an answer to the first question.

It starts with simply observing the plants. You can vary the dosage from crop to crop or between plants in the same crop. Plants with leaf tip burn will generally have too high of a concentration and plants with pale leaves will generally not have enough nutrients. This assumes other factors like pH are correct.

Another option is leaf/flower/fruit analysis. For example, if you're growing spinach, you may view iron content as an indicator of quality, healthy plants. Determining the iron content of the leaves from plants dosed at different rates will help zero in on the optimum fertilizer program.

The best way, IMO, is to test the nutrient solution before and after it has been "fed" to the plants. This requires a recirculating system for best accuracy, but runoff can also be collected in a drain to waist system. As the author mentioned, unused nutrients will build up in the solution. An ideal solution will have the nutrients used by the plants at the same ratio they are found in the virgin solution. Any skew from that over time will indicate which concentrations should be adjusted and by how much. It can be a tricky beast, however, as the uptake rate of any individual nutrient is influenced by the presence of other nutrients. Change one and you may create an imbalance elsewhere. Like most things, it's a process.

That last part is interesting to me, how would you test the nutrient solution after circulating? Would you just pay a lab to run the analysis on what's left or evaporate the solution to increase concentration and then try to precipitate the ions left in the solution and weight those?

You'd pay a lab about $45, same as I did for my quality control check. A few of the ions--like nitrate or ammonium--will probably get tested with some kind of color-change reaction, and quantified with a visible-light spectrophotometer. The rest will be from ICP (inductively coupled plasma), a precisely-quantified version of the same effect as where different elements make a flame turn different colors.

The nutrient profiles in my calculator are copied from various academic publications. Those profiles typically come with less discussion of how they were designed than I might hope, but I assume it's from review of trials of the form mentioned in the other reply to your comment. For more profiles, I've never used anything from


but I suspect from the author's bio that it's trustworthy.

For probes, see


EC probes should last basically forever if correctly excited (zero net DC). pH probes are consumables, but my $10 probe is still happy after a year continuously immersed. As process fluids go, hydroponic solution is pretty mild, neutral-ish pH and decent ionic content.

I bought the potassium nitrate from MBFerts in combination with other fertilizer salts, so if I'm on a list it's probably "cannabis growers" and not "mad bombers". If you'd rather not use it, then a quick experiment in the calculator shows you can still hit a decent profile with just calcium and magnesium nitrates.

Very interesting, thanks!

I'm curious to know how stable the blend of elements in tap water is. Do you have any data around this?

I once used an inexpensive electrical TDS meter (total dissolved solids) to track the amount of non-organic solids in water both before and after filtering over time. My goal was to determine the rate at which to replace the filter, and it turned out the manufacturer's recommendation was perfect. However I did notice that the unfiltered water's measurement fluctuated a lot over time. Could that pose a challenge in your scenario?

Thanks for a great read, btw.

I have a drain-to-waste system running open loop, with a constant dose of acid and sensors monitoring the pH of the leachate that drains from the pots. In that system, I've seen step changes in that pH that I believe correspond to step changes in my source water, perhaps when my utility changes which wells supply me. Hard to say without a detailed water analysis, but I'd guess the changes in nutrient profile (e.g., ppm Ca) aren't too important, and that as long as I adjust the acid dosing to maintain target pH the plants won't be affected much.

A single well may also show gradual seasonality, like from snowmelt and such. I assume that's happening too, but in my current setup that would be hard to distinguish from gradual pH variation due to changes in the plant nutrient uptake.

Wow, do you have more resources for the drain to waste system?

Nothing exciting--the plants drain into a 1020 tray, and a pump sucks up the leachate. The pump feeds into a waste bucket, through a sample cup that contains pH and EC electrodes. (It would be more common for the leachate just to drain by gravity, but the pumps made best use of my limited balcony space.)

If you got a reverse osmosis filter and thereby worked with neutral water as a starting point, would it be easier to achieve your target ratios? You wouldn't have to account for existing concentrations in the tap water.

Also, I was under the impression that there are two stages for plant growth: vegetation and fruiting. The two stages have different requirements for nutrients:

- high nitrogen, mid phosphorus, low potassium; and - low nitrogen, mid-high phosphorus, super high potassium

respectively. Do you use the same mixture for both stages?

Reverse osmosis water solves a lot of problems. Household RO systems are pretty wasteful, though; the pressure across the membrane is just the household water pressure, so the ratio of waste:purified is around 3:1. Fancier RO systems with pumps achieve higher pressure, and thus more favorable waste ratio. Those professional systems are way too big for me, but perhaps I could build something.

I believe that professionally, RO isn't used to solve excess calcium, carbonate, sulfate, etc., since it's cheaper just to neutralize the carbonate with acid and adjust the fertilizer salts appropriately. RO is used to solve excess sodium, chloride, etc., since the source water is already above the final desired concentrations.

I'm running a single nutrient profile for all my plants, regardless of life stage--I can scale all the element concentrations together, but I can't adjust the ratios. My yields would be better if I adjusted as you say, though. At some point I should add a third fertilizer part and dosing pump.

Very cool project!

Do you know if there are any benefits of growing hydroponically compared to the conventional (farming) methods? Is it economically interesting? Is it more sustainable?

Uses 5% of the water (few losses to evaporation)

Time to harvest is typically 2-3x less / faster.

Yields are 2-3x in volume (targeted nutrients, more hours of "sun")

Can grow small without a yard (ie Condo, Apartment, Townhouse)


Much less interesting than this formula, but I grow with an Aerogarden.

Takes ~2 weeks to 1st Harvest, lives on a bookshelf in my living room, 6 plants produce a salad for 2 about 1x a week. Lettuce is flavorful. I expect a single "planting" to last about 4 months (having done this a few times)

In comparison to my outdoor winter crops (including Kale and Broccoli) , all planted around October 7th; Outdoor Kale and Broccoli aren't to first Harvest yet (estimated ~60 days)

Very clear, thanks!

Very cool. Do you have any pictures of the full hydroponic setup (with plants)?

There's one in my post about the automation system, at:


That was still with the old commercially-blended nutrients, though. I've so far used my custom blend only for a few bok choy, as a final quality control check since they're fast-growing. If those continue to look good, then I'll move my entire balcony to the custom blend in about a month.

Regarding the automation, I built a DIY closed loop distillation process with similar i/o requirements. I have nowhere near the skill required to build a dedicated board but found that node-red running on raspberry pi using mqtt to talk to nodemcu running tasmota created an extremely extensible and modular platform. I’m running 8 thermocouples, two pumps, two flow meters, two load cells, current sensing coil and zero crossing ssr to chop current to a 6kw 240v heating element. With tasmota the little mcus are just kind of like legos and i just put them where the wiring is convenient and keep some spares.

All of the i/o is dumb, the control loops are all on the node-red flowgraph allowing for lots of visibility of terms when tuning pids.

The node-red dashboard lets you mix telemetry and control on a very touch friendly format, and i spool all of it to influxdb to compare runs over time.

I’m sure you’ve got what you need with what you’ve built but at a minimum node-red might be worth a look. I was suuuper impressed using it for this.

That seems like a perfect use of node-red. Your setup sounds pragmatic and effective; I’m sure there would be an audience for some kind of write up with diagrams, especially if it also functions as a node-red tutorial (of sorts). I know that I am regularly designing control systems for hobbyist ag setups, and I pretty quickly hit a wall due to having minimal coding background. Something like node-red seems really useful for someone in my situation. Thanks for the ideas!

It really makes the most out of the flow-programming paradigm and the integrated UI bits are really convenient.

The architecture is pretty straightforward. MQTT over wifi acts as a message bus between node-red and your 'legos'. (You don't really even need a raspberry pi, you just need to be able to run node-red, an mqtt broker and have wifi. I ran everything from containers on raspberry pi and ran the pi in AP mode which kept everything self-contained and tidy.)

For the i/o 'legos', i had more luck with the esp8266 than esp32's on Tasmota, but things have probably improved since then. You could also look at espurna, esphome, home assistant, etc. Main thing to look for is a firmware that supports some kind of async messaging protocol that nodered supports and has the i/o you need. You can buy a six pack of nodemcu esp8266's for $20 off amazon.

Good luck and have fun!

The tomato plant is huge! It seems quite foliage heavy though, do you think that's because of the commercial nutrient blend you used? Have you also looked at modifying the recipe at different stages i.e. during growth, flowering, ripening?

What climate zone are you in (if you don't mind me asking)?

I'll be growing a bunch of things in Spring and would like to make a setup like this. I'll keep an eye on the project and likely contribute if you're open to it

> It seems quite foliage heavy though, do you think that's because of the commercial nutrient blend you used?

Mostly inadequate pruning, I think--I was planning to replace it soon, so I'd gotten lazy. Normally I remove side shoots and lower leaves, for less foliage and better yield. The fertilizer was Masterblend 4-18-38, which is intended for tomatoes and pretty close to the University of Florida's "Stage 5" tomato profile (per their article linked from my calculator). So I'd guess the nutrient profile was close to optimal, except for all the excess phosphate from my pH down.

I'm on a somewhat protected balcony in San Jose, USDA Zone 9B. That's warm enough that I can grow tomatoes through the whole winter, as long as it's a cold-tolerant cultivar (e.g. Early Girl; or Sub-Arctic Plenty, which is a determinate so needs less/no pruning), and lots of other stuff too.

And contributions definitely welcomed, especially on the controller firmware. That's currently in a state that's useful only to programmers. More work there (integration with home automation software, a nice browser-based interface to schedule irrigation and dosing, etc.) would make that accessible to a lot more people.

also interested in seeing pictures/diagrams of the setup

Very cool. Thanks for putting this together.

It takes a lot of patience, and good IPM, but living soil has been awesome to me. We often say we grow soil, rather than plants, because of the fact a healthy living soil will provide all the nutrients the plant needs, and all you have to do is water essentially. Speaking strictly from a marijuana perspective (the limit of my experience with living soil), it makes the marijuana taste better and have a better smell. I've seen two different growers, starting with the same clones from the same mother planet, where one grows in soil using bottled nutes, and the other does living soil. The living soil definitely was superior.

With that said, living soil is not practical for everyone. Trying to do it indoors where you also live could create issues if you do not have a good IPM strategy, and fully understand the soil food web. "Teaming with Microbes" by Jeff Lowenfels is an excellent book to learn about how the soil food web works.

So long growers are maximizing THC content and yield per area Hyrdo will outcompete organic soil. Personally I grow organic because I too prefer the taste and I really enjoy composting. However having grown in hydro I can tell you that plants grow bigger, faster, and more potent.

> So long growers are maximizing THC content and yield per area Hyrdo will outcompete organic soil

In my case that's a feature and not a bug of soil-grown marijuana. I'm way more of lightweight compared to my college days and would prefer good taste over potency.

I think is because of the oxygenation of the roots, do you think that an organic fertilizer will necessary give lower yield?

I agree with @wefarrell that it generally gives a lower yield. It can also be very difficult to do living soil on scale, but there are definitely plenty of businesses doing it. Closest to me, in Ann Arbor, Michigan is a place called Apothecare that does living soil on scale for example.

Based on my experience yes.

IPM = Integrated Pest Management

What do you do about spider mites?

Sns217. Spider mites like it dry, so mist your plants and it may be a little wise to repot your plants or fertilize with cal/mag

Outside of light, nitrogen (N), phosphorus (P), and potassium (K), or NPK for short

Finding the right combination of these elements is what hydroponics farmers do everyday, pushing the limits of their crop for maximum quality/yield. We are starting to see a big shift in hydroponic fertilizers from liquid to powder since nobody wants to pay for shipping water.

I highly recommend https://github.com/kizniche/Mycodo for anyone doing anything in hydroponics.

> Outside of light, nitrogen (N), phosphorus (P), and potassium (K), or NPK for short

Ehm. Check out this Nature article on the importance of Carbon:


Very readable and worth reading in full. Especially the effects of elevated CO₂ on the C₃/C₄ photosynthetic pathway and crop yields.

Hydroponic growers are intimately aware of the need and benefits accruing from elevated CO2. You'd be hard pressed to find a greenhouse vegetable farm without a huge CO2 tank outside, as well as the technology used inside the scrub carbon dioxide from natural gas exhaust and reroute it into the plants. They tend to burn the natural gas during the day to feed the plants while storing the heat in huge water tanks to warm facilities at night.

The primary constraint is maintaining low enough CO2 levels to remain healthy for the humans that work inside the greenhouse. Plants themselves can handle very high levels of carbon dioxide.

What about global warming from this greenhouse gas?

If you are concerned about CO2 emissions from hydroponics, I have bad news for you regarding every other activity in an industrial society that consumes electrical power or requires heat. They all produce enormous amounts of CO2. That is why global warming is happening.

If you would like that to stop happening, I would suggest working on a ban on petroleum drilling, or a carbon tax.

They were going to burn it for heat anyway. This produces less CO2 than getting it from a tank.

The article lists 16 required elements: C, H, O, N, P, K, Ca, Mg, S, Fe, Cu, Mn, Zn, B, Mo, Cl.

In what forms?

Nice work. I really admire your hardware setup. However it's worth adding that most of blooming plants will change their 'diet' during their flowering period. Some will continue to grow through the whole cycle on one mix and other (like tomato, cannabis) need some additional nutrients dj'ing. I've been growing succesfully 'passiflora edulis' in hydroponic setup for 3 years (continuously) and still I'm using hydroponic as a great kindergarden for most of my new plants.

> However it's worth adding that most of blooming plants will change their 'diet' during their flowering period.

Yeah, absolutely. I tend to grow a lot of different plants at different life stages, so an optimal profile for each one would be a lot of work. I'm certainly paying a cost in yield for my laziness, though.

At some point I should redesign my nutrients into three parts. I've got support for a fourth dosing channel (fertilizer A, fertilizer B, pH, spare) in my electronics, so it's just another pump and the plumbing.

I came by a book on "micro-propagation" once (getting diced up plant samples to root in a petri dish) - it discussed the old fashioned way to propagate orchids (once you have a mutation you like, you have to clone that one plant by however many you want to sell) - apparently coconut water was used as a nutrient medium.

Found a source that discusses its use [0], apparently is has beneficial hormones as well, "Besides its nutritional role, coconut water also appears to have growth regulatory properties, e.g., cytokinin-type activity"

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6255029/

What's insane to me is how much certain plants will grow in tap water with zero regard for their nutritional requirements. I frequently propagate houseplants by putting cuttings in a glass of water and sometimes I get lazy and don't re-pot them for weeks or even months. And they will often grow very well - shooting out tons of roots but also additional leaves and stems.

I think that's not by accident. Typical houseplant species seem to be selected for their ability to look good with minimal fertility. That makes them easier to grow, but harder to grow optimally. For example, mint will quickly indicate any deficiency in its leaf appearance, but pothos / devil's ivy will mostly just grow slower.

That’s the same as saying there are animals that have more biological fitness (mice) than others (pandas). Carbon and nitrogen come from the air, water will hydrate them, but most plants have expectations.

Orchids for instance can be artificially bloomed with phosphorus but if it was dormant people would just think it’s dying, as if natural cycles of less bloom was a failure of the plant’s growth!

I believe it takes most of the material for air, not water.

Bottoms of green onions to me are the weirdest. You can get multiple cuttings just from water.

Hard water is actually one of the worst things you can give to expensive house plants, distilled water is by far the best option to prevent root calcification and ph swings.

Don't know why I got this reply? Green onion bottoms that normally would go into the compost aren't expensive, and the tap water here is very soft.

You can also acidify the water down to a reasonable pH, though even phosphoric acid is somewhat dangerous and the best choices (nitric or sulfuric) aren't something I want in my apartment.

Amateur hydroponic growers often use reverse osmosis water, somewhat wasteful but cheaper than distilled. You can get RO systems designed for aquarium use with no pressure tank at the output and just let them slowly fill a barrel or tote, over hours or days.

What about tap water from countries where the water is soft, like Scotland, Ireland or Norway? Or is that still too "hard" for plants?

> Sulfuric acid or nitric acid would have a more favorable effect on the nutrient profile, but they're more and much more dangerous respectively.

Sulfuric acid is not really that dangerous unless you are getting the high test stuff from a chemical supplier. You can use battery acid refill solution, it's just deionized water and H2SO4 at around 30% concentration. That's mild enough that it won't cause any immediate burns, but you should still wear gloves and goggles when handling it.

There's no need for nitric acid, since you are already supplying nitrate ions.

Yeah, battery acid is sometimes used, and not a terrible corrosive risk with the precautions you note. I don't love that it doesn't come with any specs e.g. on heavy metal contaminants, but I think it's near-certainly fine in practice. ACS grade would have specs, but I don't want to handle the concentrated acid.

Sulfuric acid would give me excess sulfate, but since the plants aren't too sensitive to that I expect that would be an improvement over my current excess phosphate. I'm not sure if I'd get calcium sulfate precipitation as the reservoir concentrated. Nitric acid would let me hit my target profile exactly (with a corresponding decrease in nitrate salts), but it's way more dangerous. I've seen nitric acid used in academic trials and in countries with weaker safety laws, but not commercially in the USA.

Yeah, it's annoying there is no purity spec on the battery acid, but in all likelihood, it's pretty pure. One could always test it.

I mean I bet nitric acid would work great for that purpose, it's just a bit more expensive and harder to get in some places, as you mention. It's definitely commercially available in the USA though.

Duda diesel has it: https://www.dudadiesel.com/search.php?query=nitric

Duda also has sulfuric which is likely higher purity, but you seemed to express some concerns about working with corrosives.

I'm a former chemist, so anything short of super angry chemicals like piranha solution, I'm not too phased :D

Brawndo has what plants crave. It’s got electrolytes


This was the very thing thing which came to mind when I read the title.

They weren't even wrong.

I would totally buy a Brawndo hydroponic formulation.

The problem in Idiocracy was evaporation concentrating the ions until there was eventually too much for the plants to grow. I'm not sure what the solution is on real farms.

Great stuff. I was thinking about this after watching a talk by the Beyond Meat CEO in which he states that instead of using animals to rearrange plant proteins into animal proteins (muscles), they're taking the animal out of the equation.

My next thought was, can't you take the plant out of the equation too? How difficult is it to rearrange these nutrients from a fertilizer mix straight into something resembling animal proteins (though easier for humans to digest)? I wonder at what point plants scale better than raw conversion of fertilizer to whatever protein these companies seem to be synthesizing.

Soilless media (commonly used for growing marijuana) was actually a game changer in my apt for indoor plants during the pandemic. If you have any issues with fungus, gnats or any kind of negative root insects soilless media is the way to go. Fertilizers that incorporate beneficial endophytes are also fascinating. However, steer clear of nutrient blends like Noot though - they're watered down and urea derived which is a great way to stress and kill your house plants.

> If you have any issues with fungus, gnats or any kind of negative root insects soilless media is the way to go.

Yeah, though with the caveat that if your medium retains water very effectively (as e.g. rockwool does) and is exposed to light, then it may grow algae. The larvae then feed on that algae, and the problem is back.

I spend a lot of time fighting fungus gnats. The best option is always to adjust growing conditions to create an inhospitable environment for them, but I also make recourse to Bti (a bacterial toxin, like mosquito dunks) or pyrethrin sometimes.

Other way to fight this issue is using a pre-made friendly fungy & bacteria mix.

What do you make this mix out of?

I don't know how to make them out. My preferred solution (used in both soil and hydroponic) is GHE SubCulture[1]

But any should work just fine

[1] https://growx.ru/images/catalog/GHE/stimylatori_i_dobavki/su...

You know how sometimes you think about something and it appears out of nowhere the very next day? That's what this article is for me. I have been growing mint, basil, purple basil and rosemary in a custom NFT system for the last 5 months and I am starting to run low on my General Hydroponics nutrients which are somewhat expensive at ~100$ for the 3 solutions.

This is very useful and I want to say a big thank you to the author for doing so much of the work I was planning to do!

When you said NFT I got triggered. Then I realized this can't surely be the NFT I'm thinking about haha.

My bad, should've known better than to use NFT on HN.

For those wondering, it stands for "Nutrient Film Technique" and it's basically running a small stream of nutrient solution in PVC tubes with your plants' roots being somewhat submerged.

It's a pretty water-efficient technique, this link explains it well: https://www.trees.com/gardening-and-landscaping/nutrient-fil...

Have you considered selling your Nutrient Film Technique on the blockchain?

It's "what molecules" a better phrasing?

"What ions", strictly--they're salts, so they dissociate when they dissolve. But it's conventional to look at the breakdown by element, not by ion, even in cases where the specific ion is important. For example, fertilizers give "percent nitrogen from nitrate" and "percent nitrogen from ammonium", not "percent nitrate" or "percent ammonium".

This reminds me.

In my layman's mind, having agriculture right next to roads is bad because vehicles are dirty.

Recently, someone told that's not the case because "plants need this stuff". Any truth to that claim? I'm yet to read the article

Plants for sure absorb things they don't need, and that are toxic to themselves and to us.

Roads used to be full of gasoline drip, heavy metals from exhaust and such. Plants would suffer but absorb it and pass it on to you if you eat them.

Nowadays not so much. Specifically around 200 times less so. Not worth consideration.

Whatever comes from the road is usually baked by the sun, so no nutrients left there. No need for that.

I can't come up with another way of analysis for this claim without it being more specific, but generally, no, that's not working today.

My childhood experiment actually comes in handy! I can confirm at the least that planting half of the same batch of seeds close to a road's (the tarmac's) edge next to it, and in a forest, my grass seeds grew much worse next to the road.

Also I was told to never eat berries growing from a bush close to a road since they are more dirty.

Great post! This reminds me a lot of making dog food for people (aka Soylent) with the best profile, requirements, and because plants don’t complain about taste, you’ll have no problem with ratios!

The only issue is about the effects of these elements and what they can do to the water or your home. Would they need a special environment to prevent fungi, algae, bacteria or mold that would also feast upon these nutrients? You said bacteria didn’t always appear but what if some will grow on hydro? What optimizations would you do for preventing infections?

Some growers keep their reservoir and root zone as sterile as possible, using additives like hydrogen peroxide or calcium hypochlorite. Others dose beneficial bacteria intended to outcompete bad stuff, like Bacillus amyloliquefaciens (Hydroguard, Southern Ag Garden Friendly Fungicide).

Algae can use the same nutrients as the plants, but can often be controlled by excluding light. Other bad microbes are generally heterotrophs, so they're feeding on something else (like dead algae or dead roots).

Is it possible to make an ecosystem that is beneficial, like kombucha in a way? Will they be using indoor lighting like from weed grow LEDs (red and blue) or you planning all/mostly natural lighting? This is a really cool project, do you have any plans with plant hormones? I only know I used rooting powder, this article is interesting! I used ethylene as well to ripen foods with bananas but I didn’t actually use them on my plants. https://untamedscience.com/biology/plants/plant-growth-hormo...

I grow mostly by sunlight on my balcony. I've also got some white LM301B lights, which seem very popular among those growing by artificial light only. Greenhouse growers supplementing sunlight still seem to prefer red-blue. You could tell a story like "some intermediate wavelengths will improve yield, and you can get them either from white LEDs or from the sun", though I'm not sure how rigorous the evidence is for that.

I don't think there's much about plant hormone use that's specific to hydroponics. People use rooting hormone and foliar sprays of plant growth regulators and such, but they do that in soil too.

Question: How do we know that we are giving plants everything "we" need?

We get nutrition through the food we eat and there are many, many molecules that contribute to our health. This project is cool but I worry about subtle nutritional deficiencies if this food ends up being the majority of a diet.

I have the same worry when it comes to lab-grown meat.

I work in hydroponic farming. If you live in the US then the produce you find in a grocery store has been grown and harvested in severely suboptimal conditions for human nutrition. Outcomes will vary across hydroponic systems but you will see in a few years that produce grown hydroponically under natural light 1) has higher nutritional density, 2) tastes better, 3) has a longer shelf life. Much of this is due to being harvested when the plant is ready and transported relatively short distances rather being harvested early for multi-week cold chain transport.

Good info thanks

Sophisticated growers routinely get lab tests that provide a breakdown by element of the leaves, fruit, or other parts of the plant. This is mostly to assess plant health, but also gives an indication of the nutritional value to humans.

It's possible to manipulate the element breakdown of the edible parts of the plant over a surprisingly wide range with an appropriate nutrient solution. For example, they grow low-potassium vegetables for people at risk of hyperkalemia:


Of course the lab test doesn't indicate whether the elements are in a form available to humans. I'm not aware of any biochemical mechanisms by which hydroponic vegetables with the same element breakdown would be less nutritious, though I'm not sure how you'd prove none exist.

An obvious question would be selenium; RDA is about 50 micrograms, and the upper "safe limit" is 400 micrograms. https://www.webmd.com/a-to-z-guides/supplement-guide-seleniu...

That's an extremely trace mineral.

Where would the plants store useless (to them) elements and for what purpose?

I don't know the biology, so I can't answer specifically, but surely there are many cases of "useless" and even detrimental elements being stored in living bodies. Just look at heavy metal accumulation in animals for example.

Water in the plant, cells, really anywhere. Same thing happens when we eat or drink something. Various molecules enter our blood, organs, etc.

Wonderful job and congrats, this looks awesome. Are there any sources (books, papers, websites, etc.) you (or anyone here) can recommend for further reading about the science behind the elements a plant needs to grow?

"Soilless Culture: Theory and Practice" is a pretty good textbook. I also recommend the USDA's


That's not about hydroponics, but the theory behind sophisticated growing in containers of soil-like potting mix is almost the same.

Interesting but I feel like I'm still missing an important piece of information to use this tool. Is there a resource which provides optimal nutrient ratios for different plants?

Does someone have a system with arduino and concentration probe that match every nutriment individualy with it's exact optimal concentration ?

I've looked into exactly that sort of setup for a previous job a few years ago and the problem is that these probes don't exist for every nutrient and the ones that do exist tend to be very expensive. It wouldn't be a cost-effective apparatus unless it was set up with one probe station metering the outflow to the whole of an industrial-scale greenhouse.

Can this be used to feed a family apartment

But how can anything grow without the most important thing: Love.

That's this man's expression of love for his crop right there, what are you talking about, you insensitive dolt.

Really nice documentation, well done.

It was found that plants roots are in symbiosis with bacterias and fungus to get minerals from the ground.

I think that like us with our microbiome, the plants have evolve with their microbiome in the soil. To grow them from a chemical mixture is to oversimplify nature.

Alternatively, you could use a coarse sand bed as media and ’compost’ natural fertiliser and get beneficial bacteria and fungus going.

> It was found that plants roots are in symbiosis with bacterias and fungus to get minerals from the ground. ... To grow them from a chemical mixture is to oversimplify nature.

And it's been throughly and exhaustively 'found'/demonstrated/proven that plants grow very well in hydroponic systems. And depending on the exact plant & nutrients used, can be just as nutritious, or more, or less nutritious compared to soil grown plants (also depending on how the soil plant is grown).

Natural != the best way to do it.

(note: I'm not saying bacteria/fungi can't be beneficial)

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