Saturday, February 2, 2013

Passive Hydroponics

 Passive Hydroponics requires the least effort of any other hydroponic technique. It is, simply, hydroponics without the use of electricity. The implications for this technique are seen throughout the world. In rural areas of the world with little access to water, the water-saving capabilities of hydroponics has increased crop yield, and improved the lives of millions. Since lack of electricity and water go hand in hand, the most common technique used is some variation on Passive hydroponics. In India, for example, cotton is a readily available material, so it is used in this sub-technique: wick type.
Yes, that was an awful segue; anyway the first, and simplest type of passive hydroponics, is “wick type”. A wick, like a candle wick brings liquid from a lower position to a higher position. This works using the process known as capillary-action. Though this piece of physics is fascinating, just like all natural processes, it is beyond the scope of the blog to discuss it. So, Bing* it. The systems have a nutrient reservoir below the medium, and a wick, such as one made of cloth, wicks the aqueous solution up to the plant roots. I have made this type, but I was not very successful—or really at all.
            The second type of Passive Hydroponics is known as a reservoir system or Deep Water Culture—often shortened as DWC. This system I have also done, with varied success. 

This is one example of success. The lettuce turned out very bitter, because of how the lighting—or lack thereof—made it grow, and it was grown in summer. This was grown inside. I attempted to make another system, but while cutting the top, I cut through the bottom—if you can’t imagine how that’s possible, then you obviously have more common sense than me. (I cut it the top with a sharp knife using the container, which was going to hold water, as a platform.)  The system shown actually uses a bit of electricity other than the electricity needed for the light. I, wisely, broke the rule about not using electricity by adding an aeration stone. Perturbing the water dissolves O2 in the water—which the plants need for respiration. The roots go down into the water, to extract nutrients from the solution. In this case, it had enough diatomic-oxygen present to sustain respiration. In a system true to the point of passive hydroponics, the nutrient solution would gradually be used, while the upper roots specialize in extracting O2. So, it is entirely possible to make this kind of system for outside use, but most results show that an aeration stone drastically improves yield.
            The third major type of passive hydroponics is the self-watering-container concept. Water resides in a local reservoir, hidden from light, and a significant portion of the container contains media. This media must wick water. These types of media include: perlite; coconut coir; peat moss; pumice; and, to a certain extent, lava rock/Basalt (I’ve worked with it before).
I have a lot of experience with all these forms. The one thing that is most important is the choice of media. The media will make or break your system. What you need is a water-retentive media. Depending on your want of manual labor, the media can be shortchanged for cost, to a certain extent. If you have enough time to water every system, every day or so, then go ahead. However, I’d rather water about once a week—or once. These systems can be created. In fact, I am currently designing two low–maintenance systems. Coupled with a pH buffer, the work is very minimal.
The best types of systems for this are some kind of compromise between #2 and #3. These systems are not terribly complicated to construct either. The tools and materials for one such system—very successful—are as follows:
  1. Media—I choose LECA/Hydroton or perlite for this system
  2. 5 gallon bucket
  3. A hand-operated screw driver
  4. A larger container
  5. A trash bag

The process for constructing this is also very short:
  1. Puncture holes 5 gallon bucket with a screw driver
  2. Fill the bucket with media
  3. Fill the larger container with water
  4. Put a supporting piece of plastic, wood, etc. on the larger container
  5. If using a trash bag, rip the trash bag to allow the 5 gallon bucket to go through it
  6. Place the bucket, filled with media, into the water
  7. If needed, stabilize the bucket with tape.
  8. Make sure the metal part of the bucket is not in contact with the water
  9. Plant

After construction, it should look like this: 

Another, even simpler system was “developed” at the same time, last year.
Materials:
  1. Media—I (unwisely) chose basalt for this last year. I’m doing perlite this year.
  2. 5 gallon bucket
  3. Trash bag

Procedure:
  1. Fill the bucket with 1/3 water
  2. Put the trash bag in the bucket
  3. Put the ends around the bucket so that the trash bag envelopes the bucket
  4. Make sure the trash bag is tucked around the bottom of the bucket
  5. Poke holes in the trash bag with anything—even your finger will work
  6. Fill with media

It should look like this: 

(You’ll notice the hydroponic system did worse. It did initially, but after I stopped being stupid and watered above the media/root line, the hydroponic tomato plant produced more tomatoes. The reason for why the plant didn't grow well without water above the root line was that it did not finish growing roots into the reservoir. Once it did, I did not have to water it for weeks in the heat of august. I’ll just call it a learning experience.)
Anyway, the results I had are not exactly reliable, because one data-source does not make a trend. However, scientific research has been done on the subject. (http://www.ctahr.hawaii.edu/hawaii/downloads/Three_Non-circulating_Hydroponic_Methods_for_Growing_lettuce.pdf) In this study, the concept of commercial passive hydroponics was tested. It can be summarized as: " you can use passive hydroponics in a commercial setting, but there's no real benefit other than easier assembly and no electrical input." I still suggest you read it. One very useful read is  http://www.diy-hydroponics.com/passive-hydroponics-systems.html . Good luck gardening! --Blackberries Are For Picking 
*I live in the Pacific Northwest, I'd be a "traitor" to not respect the MSFT overlords. 

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