gritty mix vs semi-hydro comparison?

greentoe357February 7, 2014

Has anyone tried both gritty mix and semi-hydro method and can compare the two? I have used the former and like it for most of my plants, but what am I missing by not using semi-hydro method? I grow a bunch of different house plants, mostly tropicals. My interests going forward lie primarily with hoyas. I grow indoors, and during the heating season the air gets pretty dry, so I am concerned how often I'll need to water if doing semi-hydro.

I posted a more general semi-hydro questions thread here ( - check it out if you have a s-h bug), but there are a lot of gritty mix people here as well. Too bad there's no separate "Semi-hydroponics" forum. Thanks, all.

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nil13(z21 L.A., CA (Mt. Washington))

gritty mix and "semi-hydro" are both just hydroponics. There doesn't need to be a separate forum because semi-hydro is just hydroponics and there is a hydroponics forum.

    Bookmark   February 7, 2014 at 10:53AM
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gritty mix and "semi-hydro" are both just hydroponics.

My understanding is all three are distinctly different.

Hydroponics pumps water multiple times a day or even continuously into the roots. Semi-hydro is a passive system where an inch or so of water is allowed to stand at the bottom of the pot, and that forms a reservoir for passive wicking up into the roots.

Gritty mix drains almost as well as the other two, but no standing water and no active pumping - just some water retention in the mix particles till the next watering. Closer to the good ol' flower pots, but with lots of air, very good drainage and no fast collapse of the mix, and no hydrophobia or death-grip water retention extremes either.

So, the three are kinda sorta similar but not really.

I did check out the hydroponics forum, and it's really hydroponics that I found discussed there, not what I wanted to ask about.

    Bookmark   February 8, 2014 at 9:50AM
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nil13(z21 L.A., CA (Mt. Washington))

hydroponics doesn't require pumps. What is important is how the nutrients are provided. If the nutrients are provided solely by the water, it's hydroponics. If it is provided by the breakdown of organic matter it isn't. When you start dealing with bark as a medium, you will get some provision of nutrients from the bark but in such a limited quantity so as to be effectively hydroponics.

Now different ways of providing that water will necessitate different media with varying moisture/air relationships. So if you have a recirculating systems, the medium will have much more air space. If you use a 'to waste' system, the particle size will need to be smaller for moisture retention.

    Bookmark   February 12, 2014 at 11:48AM
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nil13(z21 L.A., CA (Mt. Washington))

from the Univ.of Arizona,

"In aggregate hydroponic systems, a solid, inert medium provides support for the plants. As in liquid systems, the nutrient solution is delivered directly to the plant roots. Aggregate systems may be either open or closed, depending on whether surplus amounts of the solution are to be recovered and reused. Open systems do not recycle the nutrient solutions; closed systems do.

In most open hydroponic systems, excess nutrient solution is recovered; however the surplus is not recycled to the plants, but is disposed of in evaporation ponds or used to irrigate adjacent landscape plantings or wind breaks. Because the nutrient solutions are not recycled, such open systems are less sensitive to the composition of the medium used or to the salinity of the water. These factors have generated experiments with a wide range of growing media and the development of more cost-efficient designs for containing them.

There are numerous types of media used in aggregate hydroponic systems. They include peat, vermiculite, or a combination of both, to which may be added polystyrene beads, small waste pieces of polystyrene beads, or perlite to reduce the total cost. Other media such as coconut coir, sand, sawdust, are also common in some regions of the world."

    Bookmark   February 12, 2014 at 12:24PM
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so to clarify based on the above, if i use a soilles mix containing various quantities of peat/bark/perlite/scoria/coir/etc and use a wick dropped in water-solution containing a liquid fertilizer or use a wicking mat with same solution (both for sub-irrigation) to provide nutes - is it a closed hydro then ?

    Bookmark   February 12, 2014 at 8:15PM
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nil13(z21 L.A., CA (Mt. Washington))

I would say so. I definitely think it would be beneficial to consider it as such.

    Bookmark   February 12, 2014 at 9:40PM
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oh! goody-go-ood! it's nice to be boxed ;) finally i know where i belong!
but i can tell you that there are not many people posting about it. and hardly anything in hydroponics.
there it is about pumps and aero and mostly automation. which i understand is very attractive on a larger scale with more room to spread out!
but 'semi-hydro' is like a different niche. i would call it semi-hydro, only because there's water and there's a solid medium above that water AND roots are not in the water per se.
i would put it in a sep forum, just because it's passive :).

    Bookmark   February 12, 2014 at 9:55PM
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Jay Part Shade (Zone 10B, S21, Los Angeles)

Hey, to chime in, I wouldn't call gritty or 5-1-1 semi-hydro. Semi is usually reserved for hempy buckets, pure coco, etc. Those are mediums that must be fed with typical hydro nutrients and must be PHed constantly. There's very little room for error but the results are great. They're almost always "drain to waste" systems (aka poor man's hydro), rather than recirculating.

5-1-1 and gritty just replace potting mix, orchid mix and cactus mix sold at garden centers. No one labels these mixes as hydroponics. When I buy trees, they arrive in either a 5-1-1-like mix or a heavy granite/bark mix. This isn't hydro, the growers aren't PHing with every watering, they're not doing nutrient calculations, etc.

Additionally, one can feed organically (through liquid and powdered ferts) the 5-1-1 and gritty mix. It's not like growing in pure perlite. There's enough microbial action and water retention to "feed the soil."

To answer your original question, I haven't done a side-by-side of 5-1-1 and semi, but I have a friend who might do it soon. Really, semi or full hydro usually yields better results, but the margin for error is much greater than traditional mixes.

    Bookmark   February 13, 2014 at 10:52AM
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nil13(z21 L.A., CA (Mt. Washington))

you might not consider a passive system with various organic media hydroponics Jay, but the researchers in Universities do because the nutrients are supplied through water.

Drain to waste or open systems don't need to ever be tested for pH, let alone be tested constantly. Only recirculating systems need to be tested constantly. Open systems are not 'poor man' systems. Most commercial tomato and cuke growers use open systems.

Just because no one labels something as hydroponics doesn't mean it can't be used for hydroponics. That is an ad populum logical fallacy. They don't label it as such because it would scare the majority of people that have a misperception of what hydro is and is not, like you.

Growers are most certainly doing nutrient calculations when mixing up nutrient solution for injection or figuring out CRF additions to media.

yes you could feed the plants with decomposing organics when using an organic medium, but if you aren't then you aren't and that argument is irrelevant. If universities consider an open system with sawdust as medium hydroponic because the nutes are supplied through fertigation, why would it matter that I could use that medium conventionally if I added manure to it?

    Bookmark   February 13, 2014 at 11:17AM
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nil13(z21 L.A., CA (Mt. Washington))

petruska, there are water based hydroponic systems like Kratky and Nutrient Film where the roots are in the water, and there are aggregate systems like flood and drain and open to waste systems where the roots are in the medium and not in water. Roots being in water is not a necessary condition for a system to be considered hydroponic.

    Bookmark   February 13, 2014 at 11:39AM
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Jay Part Shade (Zone 10B, S21, Los Angeles)

Hey Nil, I'm sure you have more experience regarding university studies and whatnot. I think it's important to recognize that the original poster is not a grad student or setting up a large commercial growing operation. He's just a hobbyist looking for general advice about different mediums. And, in common usage, 5-1-1 and gritty aren't considered hydro or semi-hydro.

5-1-1: replaces generic potting mix, Miracle Gro, etc.

Gritty: replaces orchid mix, cactus mix, etc.

Semi: perlite, lava rock, coco, etc.

And I believe you're incorrect about pHing semi hydro drain to waste. The nutes have to be mixed correctly and you test the waste water to see how much the growth of the plant is causing pH fluctuations. At least, a friend's coco grows do this, maybe if your nutes are perfectly pH balanced it's not needed, but that's not the case in all drain to waste systems. Again, this isn't my specialty. That said, Gritty and 5-1-1 are both drain-to-waste mediums and they need to be pH corrected, right? And if there's an issue, you need to check and adjust the pH.

Also, from a purely academic point, referencing your earlier post, hydro is usually done in a medium that doesn't break down. 5-1-1 and gritty break down, from moisture and microbes, not compacting. I believe that's the defining line of hydro, but I could be wrong.

More importantly, defining hydro as simply feeding through water doesn't make sense to me -- then every synthetic fertilizer would be considered hydro. But they're obviously not since synthetic fertilizer is the number 1 commercial means of growing in soil. Feeding through breakdown of organic matter is just "organics", it's not the opposite of hydroponics. One can do organic or synthetic hydro just as one can do organic or synthetic soil.

    Bookmark   February 13, 2014 at 11:44AM
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nil13(z21 L.A., CA (Mt. Washington))

if you are making your own nutes using individual chemicals, then yes you will want to test the pH initially. However once you have a recipe, you don't have to test. If you want to reuse nutrient solution in a to waste system, then yes you would have to test the pH. If you just drain the waste to say landscape plantings then no you would not test that.

Hydro is usually done in an inert medium. However, as the u. of arizona quote above shows, non-inert media like sawdust can be used. I will agree that the line between hydro and conventional starts to be blurred by using non-inert ingredients. But I think that the intent of the nutes being used helps clarify that. If you are using nutes that don't require biological breakdown like nitrates it's closer to the hydro bright line. If you are using nutes like urea that do require breakdown and will work on the medium it's closer to the conventional bright line. there is definitely a continuum.

Not every synthetic would be hydro. Urea and ammonium are going to require biological activity (yes you can use those in a recirculating hydro setup but the results are generally not great). Those are the most common synthetics used by commercial growers. Nitrate based hydro nutes are much more expensive. A lot of commercial growrrs also use composted bark for moisture retention. That combo is much more conventional than hydro. Those media breakdown quickly and they have to repot evey season.

that last bit about organc and synthetic is just confused because of the erroneous vernacular use of 'organic'. Organic hydroponics are just nutrient solutions of immediately available nitrates from 'organic' sources.

The whole semi thing cracks me up a bit. 20 years ago if you walked intoa hydro store you would find decorative cotainers for houseplants that were passive systems that look exactly like the semi containers. They were rightly called hydroponics. They were usually from Europe and they would be filled with hydroton or leca. Then along comes one orchid grower in the US that felt that people were afraid of the word hydroponic does the same thing and brands it semi-hydroponics and puts it on the web and poof, people start calling passive hydroponics, semi-hydroponics. Of course, all the people in Europe that are still doing the same thing are doing passive hydroponics. Books on hydroponic houseplants still refer to that system as hydroponcs. But that guy sure gets a lot of hits because he convinced people that semi-hydroponics is something different than what people have been doing for decades.

    Bookmark   February 13, 2014 at 12:40PM
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this is all very educational, but if we were to get back to OP - what would be advantages and disadvantages of gritty/511 vs passive hydro with aggregate (marketed in US by semi-hydro) ?
what plants and under what growing conditions (indoors/outside/greenhouse...var climates) are more suitable for one or the other?
we still have no answers.

    Bookmark   February 13, 2014 at 1:05PM
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>> this is all very educational, but if we were to get back to OP - what would be advantages and disadvantages of gritty/511 vs passive hydro...

HAHA thanks Petrushka.

As it happens, I just placed an order for a bag of Growstones, and I already have gritty mix, so Ms Cleo sees some experimentin' in my future!

In other news, I went to a local Orchid Society meeting yesterday for the first time ever, and when a topic of soils came up, I asked if anyone grows semi-hydroponically. The whole room of otherwise very experienced growers went silent for a second, then several of them told me not to waste my time. Which makes me even more interested to "waste my time" on this now. It's really amazing how all over the map the opinions on semi-hydro are. Of course, there is also a chance that they've never heard of it, do not know what it is and did not want to admit it. I dunno.

Seems like even people who do know what it is can't even agree on basic rules, for example on how often s-h pots need to be watered.

So, yeah, lemme get my white coat...

    Bookmark   February 13, 2014 at 1:39PM
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nil13(z21 L.A., CA (Mt. Washington))

511 is fairly conventional. it retains a lot of moisture and can be overwatered. But you can also use conventional fertilizers that are urea or ammonium based. It is the medium that most closely resembles what people would recognize as potting soil. It is possible to use controlled release fertilizers.

Gritty is an aggregate medium. You are going to have a much more difficult time overwatering than with 511, depending on the plant. You can use urea and ammonium based fertilizers but IMO you will have better results with a nitrate based fert. Now it is definitely possible to overwater gritty. if you were to use it in a recirculating hydro setup, you could have problems with air space. Gritty holds a lot more water than people give it credit for. It is well suited to an open 'to waste' hydroponic system. It is possible to use controlled release fertilizers.

Passive hydroponics like 'semi-hydro' is not a medium but a system. The medium is either LECA or hydroton. These are large particles. They are also used in recirculating hydroponic systems. However, using LECA in a recirculating system for say orchids would kill a lot of orchid species. Using it in a passive system can work but there are issues with different brands. In a passive system the ability of the medium to wick moisture is very important. Some brands wick better than others. This can account for some people's success or failure with passive systems. Those that don't wick well will dry out very quicky. It is also difficult to wet the medium well with normal watering practices. This is why the 'semi-hydro' system uses a small hole on the side. You can fill the container with water and it slowly drains out the hole on the side allowing the medium to saturate. I think a lot of old school orchid growers see hydroton as a gimmick. Or they tried it and failed because they didn't change their habits that they honed over years for a different medium. I don't know, but I would think CRFs would be problematic with a LECA type medium, but don't quote me on that.

    Bookmark   February 13, 2014 at 4:25PM
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>> CRFs would be problematic with a LECA type medium

Yeah, they would. The granules would just mostly fall into the reservoir and mess it all up. Weak water soluble fertilizer should be used with every watering in semi-hydro, from what I read.

    Bookmark   February 14, 2014 at 2:13PM
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