Step 2: Plant Food 101

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This article discusses nutrient solutions available for hydroponic gardening.

Water alone is not enough to feed a plant. Distilled water, in particular, lacks the minerals and nutrients which make flora thrive.
In systems where the substrate is allowed to moisten and support roots, the substrate itself may be permeated with nutrients and minerals. In systems where there is no substrate, or the substrate is simply provided to support the plant physically, the water must be saturated with store-bought or homemade nutrient-and-mineral solutions.

The PH of your solution is important for the health of your flora, and the maintenance of your equipment. Your water/nutrient solution should have a final PH between 6.0 and 7.0.
These solutions usually contain varying quantities of potassium nitrate, calcium nitrate, potassium phosphate, magnesium sulfate, iron, manganese, copper, zinc, and nickel. Potassium, especially, assists with healthy root growth. Salt is an important (but often forgotten) addition to the solution, as it tends to improve the taste of the plants grown.

Store-bought liquid-soluble fertilizers are readily available at your local big-box greenhouse, nursery, or hardware store. They work well enough, but they can be expensive, or simply may not be available.

The rest of the article will discuss making your own fertile solution.

A popular, homemade recipe consisting of accessible ingredients is available at your disposal. I daresay it's not the most eco-friendly option, but it's quick and easy. For every gallon of water your system requires, add two teaspoons of Miracle Gro and 1 teaspoon of epsom salts.

I've always found semi-symbiotic relationships both fascinating and convenient.

On a controversial note, human urine can be used as a nutrient solution. Remember, the body filters everything you eat and drink, expelling toxins and retaining the essentials. If you eat something slathered in pesticides, you'll be urinating it out later. If you use that urine to grow spinach, you'll re-absorb it when you eat it. There are risks involved. Do your research.
You'll need to have a sample of your pee tested by a floraculture lab, of course, so you may need to adjust your diet. Vegans will find their urine more appropriate for plant growth than their animal-product-eating companions.
If the plants you are growing are intended for consumption, you will need to find a way to treat and sterilize your urine, making it less of a biohazard. Introducing nitrous bacteria, and diluting the solution, will help break down the ammonia prevalent in your urine. Circulating it through a biofilter will do this. Alternatively, you may be able to find an ammonia treatment in your local aquarium store.
Wanna learn how to build a biofilter? I'll get back to you on that one.

You might consider using your hydroponic system in lieu of a filter for a fish tank, hooking up a circular system filtering fish water through various substrates. There are three kinds of filter medias used in household tanks-- mechanical, biological, and chemical.
Mechanical media is used to filter out solid matter-- chunks of substrate, algae scrapings, what have you. Sponges and fibrous materials (rock wool, for example) work admirably in this fashion. Consider inserting a sponge or somesuch in each plant's drain, to reduce the risk of clogging your system, at the very least.
Biological filters are meant to encourage colonies of healthy bacteria, and control levels of ammonia, nitrites and nitrates prevalent in fish waste. Your plants will be glad to serve this function.
Chemical filters clean your water of unwanted color and odor. Unfortunately, it also excels at removing the trace elements which allow plants to thrive. You won't need it.
If you already have a fishtank, you could simply use the water you would normally siphon off and discard during cleaning, and use it to top off your hydroponics system. If your fishtank filtered, you'll have limited success with this technique.

In the meantime, consider this: a successful hydroponics system will grow plenty of plant matter, and much of it will be consumed. What little waste there is, could be recycled back into the system (accompanied by other waste matter) with the help of another animal: the worm.


Vermicomposting is a composting technique in which live worms are used to turn food waste into fertile soil. A handy by-product of the process is a nutrient-rich liquid commonly referred to as "worm tea".
Obviously, this bin won't be for composting materials from your hydroponic system exclusively-- your kitchen scraps should go in, too. Waste not, want not!

Vermicompost can be suitable for indoor and outdoor composting. If maintained properly, a good vermicompost system will not stink the same way traditional compost can. The ammonia smell we commonly associate with compost is only prevalent when the wet waste content (rotting detritus) of the bin overexceeds the dry matter (paper or plant fiber) mixed in. Worms-- red wrigglers in particular-- like to have soft, dry bedding like shredded paper or coconut fiber available to them, anyway. A stinky bin usually means unhappy worms.

There are many ways to compost in this fashion, however, for the intentions of this instructable, we will focus on the relatively uncomplicated "non-continuous" vermicompost bin.
This system is usually very small and easy to build, but if you plan on using the worm castings as well as the worm tea, you'll need to dump out the whole container after draining it. I would highly recommend transferring your worms and a small portion of the castings to another vermicompost system of any other build type, after dumping.

In order to harvest liquid worm tea (instead of distilling it from worm castings in a water bath) you will need a large plastic bucket with a draining tap and a lid. Plastic is nonporous, unlike wood, so it shouldn't absorb the valuable tea. That old, giant thermos football players bully their waterboys around would do the trick nicely.
Non-continuous systems like this can be very simple-- they're just an undivided container layered from the bottom up as follows: sump, bedding, worms, wet waste, dirt.
The bottom layer-- the sump-- should consist of a two-inch deep level of small stones and gravel. This area will be rife with crevices liquid can settle into, to drain at your convenience. A layer of fine mesh should be placed over this level to prevent the worms and their solid castings from falling into the sump. Mesh should not be placed between any other levels.
Worm bedding, as mentioned earlier, is typically three inches of loosely-packed shredded paper or coconut fiber. This level will help aerate the mixture, lower fragrant nitrogen levels, and allow your worms to thrive.
Your wet waste should never include meat or dairy product like cheese or yoghurt. Frankly speaking, those things stink when they decompose, which they do quickly because of their high protein content. Genuinely putrid food is toxic to worms. Beans are also high-protein, and dangerous as such. Oils and fats prevalent in animal products will cling to the skins of your wrigglers and suffocate them.
Stick to eggshells, tea bags, vegetable peels, stale/mouldy bread, coffee grounds, rotting fruit, etc. Citrus fruit is generally considered safe, but not citrus peel-- the oil found in the skins are toxic. Banana peels are usually heavily sprayed with herbicides and pesticides, so include them at your own peril. Worms are highly sensitive to poison.
Wet waste should be covered with another layer of bedding, for odor control.

As the worms eat the rotting material, add wet waste to the top level, sprinkling with shredded paper as you go. The worms will consume what they can, and then travel up out of their castings (urine and feces) and into the new feed. Continue the process until the bin is full, and most of the edible matter has been turned into castings by the worms. Drain the sump whenever your hydroponic system requires more fertilizer.
Make sure you test the water's final PH, and adjust accordingly!
nicwitzke4 years ago
Would mineral water help with anything?
bethehammer4 years ago
Just curious if anyone has used the liquid byproduct of a biogas digester as a solution for hydroponic gardening. I am building a digester into which I plan to use kitchen scraps (no animal products) and am looking at grass clippings from the lawn. once this is broken down it would be great if I could use the resulting liquid fertilizer to add to a hydroponic garden. kind of completing the cycle... Any thoughts?
lucien2375 years ago
Just to dummy-proof the water thing... That's the formula for photosynthesis. Food making. That's all. Totally different from mineral collection necessary for cell construction. All that formula is for is making sugar to fuel the plant. It still needs basic building blocks. Also, excellent plan my friend. I'm going to build my own system soon, though a bit modified to fit in a cramped space. Hopefully hydroponics catches on as mainstream and more people will become self reliant and healthier. But enough daydreaming lol.
Healthy urine IS sterile - so why would you want to sterilise it ? Steve
dutchypoodle (author)  steveastrouk6 years ago
Good point!
Treating the urine is the important part, obviously, otherwise you'll give the plants a nasty case of fertilizer burn.
I hear now that simply allowing a bucket of urine to sit for a month is sufficient to break it down, and render it safe to use on plantlife. But that's just hear-say, alright?
I mentioned sterilization because, obviously, not everyone's urine is healthy. It's better to be safe, than sorry. Even if it's just 1% of the time.
You are pretty ill if you have infected water - I don't think you'd want to pee for your plants ! Steve
arduinoe6 years ago
"water is not enough " , why not ? everything is there and the sand and crap just holds the plant up.

the symbol equation for photo synthesis is 6 h20 + 6 C02 ----------> c6 h12 06 +6 o2

with chlorophyll and sunlight above the arrow . all the reactants are there , h20 is the main ingridient and c02 is worryingly plentifull
dutchypoodle (author)  arduinoe6 years ago
I challenge you to produce healthy, edible growth from a plant using distilled water. Go wild, sugar. I'll wait. The results are going to be pretty sad, though. As much as I'd love to cite a formula, I'm just going to let experience speak for me. Yes, the math is there-- a plant can subsist off of air and water alone. It will not thrive.
watergeorg6 years ago
I am sure that you are right about all details, and it seems to me that the whole system is planned to be perfect in every detail. On the other hand, I have 3 fish tanks, the biggest one holds 250 liters of water. I think that I cleaned it the last time about 6 years ago. The thing is that we "clean" the fish thank about once a month by siphoning out about 50-75 liters each time, and refilling the same volume with fresh water. Now to the "thing": The "old" water is reused to water our plants, as it contains enough of nutrients to make our plants grow happily. Why not use this water in a hydroponic system? It would surely do the thing?
dutchypoodle (author)  watergeorg6 years ago
I did make a brief note about this: "If you already have a fishtank, you could simply use the water you would normally siphon off and discard during cleaning, and use it to top off your hydroponics system." The answer is-- yes. Kind of. I wouldn't run a hydroponic system EXCLUSIVELY off the leavings of a filtered fish-tank, because the resulting veggies might not be very tasty. Not much salt in fishtank water, eh?
AMalePoet6 years ago
What about potential suffocation of the worms? Water tight generally equals air tight. I've seen the apartment dweller Veriform composter (somewhere)in a common storage tote with wholes in it.
jmckittrick6 years ago
Great post, only on question, do you have to dilute the worm fertilizer in water for your final product.
dutchypoodle (author)  jmckittrick6 years ago
I would like to SEE a vermicomposter capable of spewing enough worm tea to maintain a hydroponic system. You can't water a plant with undiluted fertilizer without fear of "burning" the plant. Despite worm tea's decided lack of harsh chemicals, and relatively safe PH, it probably shouldn't be the only thing your plant absorbs. I highly recommend diluting your solution. The important part; your water/nutrient solution should have a final PH between 6.0 and 7.0.
Toffy6 years ago
The use of this container is excellent. I had worms in plastic containers just for the castings and never did get the tea. The bottom of the container given me with the worms was not prepared properly as you have suggested. Now I know, and thank you for that. This is wonderful info, and I will give it 5 stars.