I haven't done this, but I have read a very little bit on the web about this method. I've seen a few different methods used from a container holding a cacti above what looked like an almost pure mason jar of water to cacti seedlings being grown in ice cube containers. http://keinhong.tripod.com/hydro-icetray.html
http://keinhong.tripod.com/hydro-lobivia.html
http://www.bellaonline.com/articles/art39153.asp
Now, many report that growing cacti via aquaculture or hydroponics drastically speeds up their growth. While I have been able to find no data as to exactly how this growth rate compares with grafted specimens, if it is found that it is remotely comparable say 70-80% the growth rate as you might find with a grafted specimen then it may well be worth experimenting with hydroponically grown cacti. Especially so if your end goal is to have a specimen that looks more natural and is on its own roots. The downside as far as I can tell is that it is hard to initially establish water roots and some sources I have found simply suggest removing the ground roots altogether or brushing the ground roots weekly to remove any rotted ground roots. Suffice it to say, it sounds difficult if one does not simply eliminate the ground roots altogether at the start. The root rot that occurs due to ground roots being kept too wet with Lophohora for example is thus mitigated as they are first removed and then only water roots are allowed to grow. Anyone who has grown any plant hydroponically knows that water roots differ from ground roots. Aeroponics is yet another idea, but I think the main idea here with cacti is that many cacti can not tolerate wet ground roots for very long. The idea of not allowing ground roots to form and instead using their water roots or roots formed in water may bypass the whole root rot problem altogether and allow for this faster growth as more nutrients and water can then be funneled to the cacti to promote more active growth.
Co2 gardening is something I have experimented with in college....C02 gardening can be done with a simple setup whereby one takes a 6 gallon glass carboy or similar setup with an air lock to prevent contamination and allow for the escape of C02. You merely place a hose over this airlock and feed the C02 thus produced over the tops of your cacti so as to rain down C02. If you not into making your own C02 via this natural method you can simply place dry ice in an airtight growing system for your cacti. The easiest method I know of doing this is to simply place a large plastic bag over your seedlings and seal your dry ice inside the bag. The absolute cheapest most inexpensive setup for a small batch of precious seedlings however is to simply create a growing chamber with a bag attached that you can seal off. Breath in and out of the bag several times and then seal up. Breath normally for a minute with your mouth away from the bag to allow oxygen to reenter your system. Now, breath into your bag again for a full minute or two at the most and seal the bag again. You have effectively increased the carbon dioxide of your growing chamber no matter which method you use. C02 enrichment thus gained can increase a plants growth by over 40%. C02 need only be increased during the hours you are providing light as C02 concentrations thus increased will serve to increase the amount of sugars the plant is capable of producing. http://www.johnsongas.com/industrial/CO2Gen.asp
The bottom line is if your growing hydroponically then you probably want to use some method of generating C02 for your greenhouse or growing operation as you are not getting all you could be out of your hydroponic setup if the C02 gases are not sufficiently concentrated enough. Expecting a 40% increase of growth is not uncommon with the simple addition of increased C02. Homemade wine, if your already making some is easy enough to use as a captured source of C02 for small grow operations, seed trays, etc. For larger operations or greenhouses though your going to have to spend $1000 +- for a good C02 generator or make a lot of wine. Cacti have the ability to store C02 and will probably not benefit as much from the increased C02 as many other plants, but they do benefit from the increase nonetheless. What is of perhaps even more importance to remember is that while your green leafed plants are releasing C02 at night, your cacti are still able to absorb this c02 so simply growing your cacti in the same room as your green leafed plants will enable them to grow faster and healthier. http://co2generator.org/co2-boost-experiment-cont
i don't know if cacti are made for aeroponics but someone should definitely do the experiment. seems like you'd need a fan in there to air them out in between sprays and that sounds about as safe as installing a hairdryer next to a bidet. i would like to see the results though.
i might try a side by side with some seedlings to see to what degree a co2 chamber increases growth for lophs. wouldn't be that much extra work. just a culligan jug, sugar water, yeast, bag, tubing and tape. thanks for the idea.
I like your idea of doing a side by side to show potential variations in growth. Given that cacti can store C02 and utilize C02 during the day as well as the night you would ideally want to keep the C02 going for the entire trial. Bumping up the heat a few degrees to encourage more growth would also encourage more growth. You don't want less than ideal circumstances to discourage your results, but whatever the case you want your control to be under the same growing conditions minus the c02 difference. Same soil, same watering cycle, same fertilizer, just a difference in C02. I think 6 months from seed should suffice to show some noticeable difference with Lophophora whereas with a tomato or other such green leafed specimen you could see very noticeable differences in growth in a mere 6 weeks. The only other thing you might have to be on the lookout for is possible cross contamination or leakage of Co2 from one batch of seedlings to your control. You want them close ideally so that they are getting the same light, etc. so I'm not sure how best to prevent that little spillage in any meaningful way that would not potentially disrupt the experiment. The obvious easy method of preventing cross contamination would be to place your nontreated co2 control group at a higher elevation, but this would change the variable of height and light.
wait now you have confused me. my understanding was that cam plants open their stomata only at night to preserve water. is this not the case for seedlings? although it seems probably any cactus would open its stomata if it's in a humid environment.
here's what i was thinking for the experiment. i will plant two identical seeds trays. the only difference is one with have a hole drilled into the side with some 1/4" tubing run to a sugar water container. the other will not. i will have to take care to ensure the hole doesn't affect light levels. i'll cover my seedlings with wax paper and then and plastic lid with holes in it so the extra air can escape though the pores. i'll place them side by side and keep all the factors the same for six months. hopefully there is a noticeable difference. i imagine there will be. i mean my hypothesis is: i imagine there will be.
I stand corrected. You are quite right my dear Watson and thank you for the clarification. Suffice it to say, that I think your experiment is spot on and I eagerly await the results.
so do they? i mean do seedlings constantly have their stomata open? can they use co2 all the time? ...or were you pulling a fast one?
C3 or CAM? Seedlings of cacti can sometimes use C3 or both and gradually go from C3 to CAM predominately or at least that is my understanding of it. This may explain why cacti seedlings are also prone to dehydrating rapidly as seedlings as this shift has not yet occurred. Similarly, humans have a fetal hemoglobin that is different than an adults hemoglobin in structure. http://www.jstor.org/discover/10.2307/27733304?sid=21105590676863&uid=2&uid=4
The basic premise is that seedlings can utilize both c3 and CAM and may in fact utilize C3 predominately or in entirety when very young. It is not known whether it is the harsh exposure to the elements that triggers a full shift from C3 to CAM in cacti seedlings or whether it is just developmental. That is my interpretation of it at any rate. What this means to me is that cacti seedlings are going to be benefited the most by an increase in C02 during the first few days and perhaps weeks of germination.
http://jxb.oxfordjournals.org/content/62/11/4037.abstract
Reading further, you can extrapolate that growing conditions do indeed affect the switch from C3 to CAM with at least some cacti seedlings such as Opuntia that will continue to use C3 up to the height of about 10 cm or approximately 4 inches in height if kept under optimal growing conditions.
those articles clear things up nicely. i would assume cam plants branched off c3 plants so it would make sense that they can use both pathways. i imagine it's a nature and nurture thing as for what causes the switch. but they definitely seem more c3 as seedlings. this makes me wonder if two year old plants would do better with 6/6 hour light dark periods to ensure they are working most efficiently.