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Understanding Hydroponics

Understanding Hydroponics
This instructable will explain household hydroponics, with the intention of growing edible flora.
In layman's terms, hydroponics is the science of growing plants without soil-- although the plants may or may not be suspended in a solid medium such as gravel, or expanded clay balls.
Soil retains minerals and nutrients, which "feed" flora, as we all know. Plant roots can't absorb dirt, however; when water passes through soil, it dissolves and collects some of the nutrient particles embedded. This "food" solution is absorbable as a liquid. As you can see, the soil itself is not an integral part of a plant's feeding cycle-- it is simply a stabilizer for the roots, and a convenient filter.

Why eliminate the soil?
Plants breathe air, just like humans. School children are taught a simple lesson: plants take in carbon dioxide, and release oxygen. The entire plant-- not just leafy material-- contributes to this process.
If not properly maintained, soil can retain too much moisture, effectively suffocating ("drowning") a plant's root system. Alternatively, if the soil doesn't contain enough moisture, the plant will be unable to absorb the nutrients it needs to survive.
The roots of a hydroponic plant have constant access to both air and water, and it can be much easier to maintain that balance since the roots are typically visible.
The average plant needs at least five things to survive. Air, water, nutrients, minerals, and light. So long as you can provide these things in plenty, your plants should stay healthy.

Growing your own food can be a rewarding experience. It's a good way to save money on pesticide-free produce, and you'll know it wasn't shipped from a third-world serf farm supporting bad business. If your hydroponic system is indoors, you can grow food during the off-season in winter, too.

That being said, there may be more efficient systems out there for the home grower. I created this instructable to inform, more than anything.
After all, if anything's worth doing, it's worth doing right. Gotta do your research, kids.
 
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Step 1Substrate 101

Substrate 101
Although not necessary for the survival of a plant, substrate can help to support a plant physically and hold it upright, either by securing the root system, or by outweighing the plant itself. There are many kinds of substrates commercially available. Check your local greenhouse or hardware store. Alternatively, there are plenty to be found outdoors, especially near bodies of water.
Even simple rock can alter the PH of your system. When checking your PH balance, be sure to check it after it has circulated through your substrate.

In the moisture-rich conditions hydroponics typically provide, substrate can be generally classified into the following categories: sandy, granular, and pebbled.

Sandy environments consist of particles between .06 (fine) and 2mm (coarse) in diameter. Even coarse sand retains a considerable amount of water (except in comparison to soil), and is not generally considered appropriate for use in a hydroponic system. If you use a pump, for example, the small particle size may lead to clogging. However, it is cheap and readily available, and, when wet, is heavy enough to provide a reasonable anchor for plant roots.
There is some absorbable nutrient in sand. Typically speaking, the nutrients latent in sand culture vary widely on the substrate's color and origin. Most sand contains a large quantity of shell fragments, and thus has a high calcium content.
Black sand usually has a high magnetite content originating from volcanic rock, known for its fertility. Orange or yellow sand might be an indicator of a high iron content.
White sand tends to be very high in silica, which helps build healthy cell walls in plantlife. Diahydro, for example, is made from diatoms, a type of algae.
Sand is semi-reusable. Sterilizing it between uses can be messy. (Sand can be sterilized by boiling it in water for extended periods of time.)

Granular particles range between 2 and 4mm. This may consist of gravel, or plant mulch.
Stone gravel makes a heavy, non-biodegradable anchor for plant roots, and is highly recommended for use in hydroponic systems. Stone gravel contains very little latent plant nutrition, just like sand. There are several grades of gravel readily available to choose from.
Creek rock and Pea Gravel consist of round, shiny stones. The smooth shape of these stones allows for great aeration and root growth, although the drainage may be excessive.
Crushed rock is typically made by crushing large chunks of limestone or dolomite into smaller pieces. Crushed rock has sharper edges than creek rock, and tends to interlock better. This tighter knit makes for higher water retention, although limestone tends to weigh less. Limestone is a strong alkali. Check your PH, and balance accordingly.
Stone-based substrate is highly re-useable. It is considerably less messy than sand to boil for sterilization.
If weight is not a concern (ie: the plants you grow are not expected to reach considerable heights) you might consider using a plant mulch, such as peat mulch, cedar shavings, or coir (coconut peat). Mulches retain a high quantity of water, but also breathe very well. Mind you, they are also highly degradable, which can lead to clogged pumps, and wood shavings often contain aromatic oils which can inhibit plant growth. Mould and algae growth poses a higher risk when mulches are involved, but pose one considerable advantage over rocky substrate: they can be composted and replaced with fresh material. It does not need to be stored. I would n't suggest re-using 'em, anyway. This is especially convenient if you use hydroponic systems exclusively to start seeds, or grow during the off-season.

Pebbled substrate measures between 4 and 64mm.
Stone pebbles have the basic characteristics of creek rock. They are typically smooth, often shiny, and the gaps between the stones make for low water retention and high aeration. The shinier the stone, the worse the water retention will be. A matte or pockmarked surface indicates a porous stone, which will stay damper, longer, whilst still providing excellent aeration. Pebbles-- especially the porous variety-- can explode when heated for sterilization.

A common alternative to these substrates is mineral (rock) wool. You've probably seen it used as insulation in housing. Rock wool contains fiberglass, and it can be absorbed into the body by inhalation-- irritating eyes, skin, and lungs. It needs to be treated before it is a tolerable substrate for plant growth. Altogether, I don't recommend its use.

As I've said, you should boil your substrate between uses to sterilize it. Bacteria love warm, wet environments and will probably thrive in a hydroponic system.
Just a heads-up, here... algae loves wet and warm (and lukewarm... and cold) systems, too, and it can look unsightly. If you care about appearances, boiling your substrate between uses will discourage blossoming, but if you use grey (recycled from previous use) water you'll be fighting a losing battle.
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43 comments
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May 8, 2011. 5:13 PMnicwitzke says:
Would mineral water help with anything?
Mar 13, 2011. 1:39 PMbethehammer says:
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?
Feb 12, 2011. 10:31 AMtincanz says:
This Instructable has lots of top-notch info on hydroponics. will you permit me to add it to my "Plants" group?
Feb 11, 2010. 1:45 AMlucien237 says:
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.
Jan 7, 2010. 6:04 AMnicktar says:
As our planet rotates, the east-west location is not only irrelevant but placing plants anywhere but facing north or south reduces the light that reaches the plants. Placing them in south(north)-eastern facing rooms will block out the evening sun, which will allways come in from south(north)-west to west (depending on season and distance from the equator), as does placing them in south(north)-western facing rooms with the light of the morning sun.
Jun 30, 2009. 8:23 AM148wmcquiston says:
Please tell me that your going to enter this into the garden competition. It is an excellent instructables (*****) and I can't wait to use the worm composting idea (I tried before and it didn't turn out well). One question though, how much and how often do I put the food and newspaper in?
Apr 30, 2009. 10:28 PMRahdzhillaxxx says:
I Like the guide! am getting the bug to do something like this. Can you remove seedlings from potting soil to transplant into a hydro medium? I have a bunch of perlite still in the bag, will this work for a medium? If not I guess I can go get me some gravel some where or a bag of river rock at lowes. And also a great worm container! My old plastic tote of crawlers will love the new home once I find a thermos like that one ! One last question, will a nursery carry a commercial hydro food? if so will they help me decide on what kind I need for which veggies I want to grow?
Jun 3, 2009. 10:23 AMarduinoe says:
"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
Jun 23, 2009. 9:57 AMkikiclint says:
Photosynthesis only requires the given formula, however the structures of every cell in the plant require all kinds of minerals. A large blend of different things creates more vitamins for you to eat.
Jun 23, 2009. 10:15 AMarduinoe says:
im not saying that it would produce good plants , but it would produce a plant . cetainly fertilizer , mineral aditives and substrate would produce a better plant . but just water would produce a small , withered under nourished plant. and who said anything about it being distilled water , especially in my area , tap water contains more minerals and vitamins than a plant could ever want , ever! and no one would buy really expenive distilled water when tap wtare by its very nature is better . satisfied stressy knickers ? way to over react , i made a (valid) statement , that was all...
Nov 22, 2009. 6:24 AMAcanna says:
I tend to disagree with this statement beyond the nutrient factor as tap water by it self in a hydroponic system attracts diseases and infestation. This is a big reason for using distilled water. When it comes to hydroponics cleanliness is next to godliness and one cannot obsess.

On the nutrient level, the trace elements in your water might be JUST enough to keep a plant alive( for a bit ) but once the plant starts taking up nutrients and the PH swings with it you have to adjust your PH almost daily in order to prevent nutrient lockout. Plant require 3 main N-P-K and 12 micro nutrients to thrive. They take up these different nutrients at different PH levels. (around 5.8 to 7.0, plant dependent)  There are more obstetrical to what you have said which in all reality makes it very impractical to state that water alone will grow a scawny plant, Not to term. Why would someone want to grow that.  But I would be willing to give it a shot to see the out come. If so just shoot me a analysis of your water so I can produce to the same. We could use either my DWC or top drip bucket systems.
Be safe, Acanna

Jun 4, 2009. 12:40 PMsteveastrouk says:
Healthy urine IS sterile - so why would you want to sterilise it ? Steve
Jun 4, 2009. 11:53 PMsteveastrouk says:
You are pretty ill if you have infected water - I don't think you'd want to pee for your plants ! Steve
Mar 27, 2009. 7:18 AMDarrone says:
A great beginner guide! Your PH suggestions seem a bit high though. A 7.0 PH is going to significantly reduce nutrient uptake is a large number of plants. Perhaps editing to mention that different plants required different PH levels, and some go as low as 5.0?
Mar 20, 2009. 4:17 PMPKTraceur says:
Just thanks for the instructable! (5starred, faved of course!) I actually know understand hydroponics! And now comes teh questions... Hydroponics consists of growing plants "In Water." Isnt using a substrate, well, cheating? Does the substrate contain/hold any nutrients? How is the growth of a plant affected by the nutritional absorbence of the substrate? What substrate absorbs the most nutrients? water? toxins? Does PVC affect the plant growth? Are there certain pumps you can use to filter the NutrientWater? Do you think you could filter a sand substrate, that is nutrient induced would grow a plant? Am I revers engineering hydropnics using only filtered sand? Is that the equivalent of regular growing? Perhaps im overthinking this? Ah screw it, its just starting spring, might as well start. Thank! -PKT
Mar 26, 2009. 6:04 AMMDisdain says:
Firstly, thank you so much for cramming all this info into one place for me. Substrate mineral content would have been an after thought to me. This entire instructable is well-organized and is going to be incredibly useful. I can’t wait to try the Bucket O’ Worms. Ok, so I’ve just gotten into hydro and I have a question based on this step. I am currently set up with rock wool sitting in expanded clay with felt wicks (it was a kit I got for xmas). So, if I don’t use rock wool, which isn’t readily available here anyway, do I just put the seedling directly into one of the substrates that you mention? And if that is the case how big should the seedling be before its put in?
Mar 15, 2009. 12:50 PMwatergeorg says:
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?
Feb 28, 2009. 5:07 PMUncle Kudzu says:
i'm another one who has been looking (for ages) for a simple and easily available nutrient recipe; Epsom salt and Miracle-Gro i've already got. thanks so much for that alone, not to mention an excellent instructable! wouldn't it be great, though, if a body could get enough of that worm tea going to grow some nice hydro-edibles?
Jan 27, 2009. 9:30 AMshmacky26 says:
If you put the lid on the cooler would't you suffocate the worms? Or could you leave it loose, but then would the worms escape?
Jan 15, 2009. 9:42 AMAMalePoet says:
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.
Oct 8, 2008. 10:52 PMquailman says:
I've been looking all over for a nutrient solution recipe. I don't care (yet) that miracle-gro isn't that eco-friendly, I just need a simple place to start. Once I get things going, then I'll look at alternatives like worm-tea. Nice instructable, I'd love another one with more expert advice!
Oct 9, 2008. 3:21 PMquailman says:
What do you know about aeroponics? or do you have a good info source? It seems like everybody wants to keep their methods secret on the subject. I'm going to try and set up a little hydro setup soon. Little apartment doesn't allow for much... but I'm really interested in aeroponics. Hopefully I'll wind up with slightly more room in the next year or so, then I really want to experiment with the two processes. Thanks again!
Nov 20, 2008. 11:12 PMBoz says:
Here are a couple of sites that you might like to view on the subject:

www simiplyhydroponics dot com/system.htm

This is a nice site showing how to build systems

http://www.jasons-indoor-guide-to-organic-and-hydroponics-gardening.com/homemade-aeroponics-system.html

Hope this helps

Nov 11, 2008. 7:01 AMxeroseven says:
Great instructable, I was with you right up to the picture at the end of step 3. You do realize that the Earth rotates on its axis, right? If you live in the West, the Sun will only be in the East for half the day.
Nov 8, 2008. 2:45 PMqxjones says:
Thank you!
Oct 17, 2008. 11:50 PMwiley coyote says:
Thanks for this very informative, all encompassing instructable and excellent links. The vermicomposter and LED lighting are very useful...and did I mention cool? I'm just a beginner and have been researching and experimenting to find something cheap and reliable and you've really gotta look to find useful information beyond the basics. Thanks to people like you and sites like this, the world will be a much better place! Okay, I'll stop know..............................
Oct 14, 2008. 5:59 AMjmckittrick says:
Great post, only on question, do you have to dilute the worm fertilizer in water for your final product.
Oct 11, 2008. 4:20 AMSpecEd says:
Very informative for a novice, i.e., ME! I bounced here from Wiley Coyote's "mosquito" hydroponics instructable, looking for more information on the topic in general. BTW, the big coolers you mention are often available at season shift (fall-winter) in big box stores for relatively cheap (<$10, if memory serves)
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