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I've read a bit online about growing cacti in hydroponics, and basically every site I found agrees that it's possible, and it should basically work like any other hydroponics: Set the plant (in an inner pot) in some substrate, like expanded clay, put that inner pot in an outer pot, fill the outer pot with nutrient solution until it reaches the roots.

However, if you grow cacti in soil, the rule seems to be that the soil must really dry out from time to time. Now I wonder: If I keep the nutrient solution filled up at all times, the cacti's roots will never be dry. Do cacti like that? Or do all the "cactus in hydroponics"-websites forget to mention that you should let the outer pot run dry every once in a while?

Thanks a lot!

Lukas Barth
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    I wouldn't bother growing cactus hydroponically, but if this is an experiment? Cactus roots are shallow. They are designed for little to no water. They store their own water. Quick rain in the desert and it sucks up water and it is fine to go a long time. 'Nutrient' water bothers me a lot. Especially if you ONLY use water with this added chemistry or fertilizer. That is way too much. Fertilizer is not food nor nutrients. Allowing them to 'dry' out is weird. This is backwards from their evolution; little sip of water and then dry out versus tons of water and then a little dry out?? – stormy Jun 12 '18 at 20:18

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Stormy, all cacti do not have shallow roots. It completely depends on the species and there are 1000s upon 1000s of species of cacti. I am a manager at a specialized cactus nursery and I can tell you that some cactus species have massive root systems or tap roots. Cacti grow on all sorts of different terrain such as mountains (i.e., Cereus peruvianus), and without strong/deep roots they would simply fall over.

Moreover, it is absolutely correct that water is withheld until the specimen's soil has completely dried out. Cacti grown away from their indigenous region(s) always carry a high risk of fungal infections, root rot etc...A fantastic way to give them a fatal illness is by providing more and more water before their soil is bone dry. It is not against their evolution. Most cacti, with the exception of epiphyllums, evolved in areas with little to no liquid water. The good news is that hydroponic systems provide the correct amount of aerated water, so overwatering is not a concern.

Plants obtain nutrients from the sun and minerals in soil, which is what is in fertilizer/hydroponic solutions. I would use a system that a built in full spectrum LED light. You likely will want to raise up the temperature of the water and you can do so with a simple seedling heating mat. They are cheap and can be placed directly underneath the water tank. These mats typically raise temperatures between 15 to 20 degrees F above whatever the temperature is in the room. This heat will strengthen and promote faster root growth. You can grow cacti hydroponically without an issue. Thanks for listening! I know this was posted a while back, but I thought other people may come across it.

-A

Austin
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I can't answer your question directly, but I have some thoughts on this topic. I was considering this a few years ago. My strategy was going to be to have the seedlings/plants poke through a box lid. Inside the box would be a mister/sprayer that would mist/spray at periodic intervals. The rest of the time they would be in the air. I wasn't planning on using any media. This method is frequently used for rooting cuttings.

I don't think the issue with cactus is too much water, but too little oxygen for too long. I know hydroponic water storage is generally oxygenated (or aerated, at least) to avoid suffocating the plant or the roots.

I encourage you to give it a try, but I wouldn't start with my best plant. I would NOT leave the water/nutrient mixture in the pots. I'd do standard ebb and flow thing where you submerge the roots for a short period and let them drain/expose them to air for the periods in-between.

All that blather aside, I looked at a few sites which seem to show cactus growing in still water. I remain quite skeptical, though.

Tim Nevins
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Cactus grown hydroponicly is attractive for what reason? Plant them in regular medium and they will thrive in the right environment. This hydroponics intrigues me though, maybe I will use my smaller PC San Pedro and clay balls and an air pump i have to see if it.increases growth! I have nutrient solution to add as well. I would add it for a day then drain and add fresh water, nutrient solution shouldn't be in the water all the time. Cactus do not like too much fertilization!

Lawrence Gasior Jr
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