After container gardening for the best part of 35 years and with all manner of plants, I have found that altering the soil mix to suit different plant types is unnecessary, much like using a bunch of different plant-specific fertilizers is unnecessary. So I pay no attention to the amount of organic matter incorporated other than what is recommended by my preferred mix, typically always on the low side. It is the drainage and water retention that is critical in my estimation and watering frequency and fertilizing will adequately address all other issues.

Life is complicated enough that dealing with all these complex machinations - and IMO unnecessary ones - takes away from the pleasure and joy of gardening.

YMMV

@gardengal48 (PNW Z8/9) Without obsessing about fine details, I think it is pretty clear that most vegetables are not going to grow well in soil with 10% organic material unless you water and fertilize them constantly. So I think you can be aware of the scale I constructed in a general way and still get benefit from that.

These organic percentages would strike most horticulturalists as being wildly large. Where do you get those numbers? Commercial ag soil is usually about 5% organic, and raised beds may allow 10-20%. Yes, you can have too much organic matter. As the organic matter degrades, nutrients are released, and the point can be reached, especially for N and P, that those large overabundances can damage plants. See for example

https://extension.umn.edu/yard-and-garden-news/compost-and-soil-organic-matter-more-merrier

https://www.gardenmyths.com/compost-is-it-poisoning-your-garden/

@daninthedirt (USDA 8b, HZ9, CentTX, Sunset z30, Cfa) I am talking about container soil mixes. The organic material in commercial farm soil in the ground is 5% to 10% as you say.

I would never add organic material into an in-ground planting unless I had paid for a soil analysis that suggested the soil had less than 5% organic material. In an in-ground planting, you place organic material as a mulch, and it's an entirely different system for watering. An in-ground planting is like a giant container that is maybe a mile deep and 10 miles wide, and the perched water table is well below the ground level of the soil. It's the same principles of physics that we use in containers, but applied on the scale of mother nature.

I got these numbers by reading extensively about the recommended container soil mixes for different types of plants, and by participating in soil mix discussions for many types of plants, most important discussions around the "gritty mix", which Tapla designed and has advocated in highly technical terms in numerous discussions here.

I have found the nitrogen problem in compost and bark soils to mainly be about unfinished compost. A well-composted bark can grow many types of plants forever without stealing nitrogen.

The links you post are making the same points I make.

Without beating the dead horse, that has NOT been my experience. For a single season, you can successfully grow vegetables in a pretty much zero organics topsoil!

As I have found by trial and error, one can definitely have too much organic material in a soil. Such a soil can easily become dry and very difficult to re-wet.

So, to the extent we're talking about organic degradation and drastic overabundances of nutrients, how are containers any different than in-ground? Organics degrade just as well in containers as they do in the ground. Everyone has seen their container soil shrink with time. That's the volatilization of the carbon in the organics there. We're not talking about perched water here. In fact, nutrients are less likely to be washed away in containers. No way did the links I posted make the points you are making.

Now, it is clear that percentages need to be defined by volume or by weight, which you have not done. Organics are lightweight, so a small percentage of organics by weight will correspond to a half again larger percentage by volume. But even then, your numbers are very high.

Yes, you can grow in zero % organics, but you'll need a lot more fertilization.

@daninthedirt (USDA 8b, HZ9, CentTX, Sunset z30, Cfa) If you use ground soil in a container it will have an enormous perched water table due to microscopic particle sizes of the clay and silt. That would kill most plants, especially if the containers are left outdoors or overwatered indoors. The container soil environment and the in-ground environment are totally different, and by focusing on organic content only you are completely missing the point.

I don't feel your questions or points are well directed or show any understanding whatsoever of container soil structure and particle sizes. I would prefer to not have this conversation with you.

If you are going to take the extreme position, it would better be done as GardenGal did it, by focusing on particles sizes in the container and then stating that you have not seen much sensitivity to the amount of organic material, I don't agree with her, but her point is extremely relevant and coherent and shows an understanding of container soil science. The questions you raise about organic degradation are not relevant. Overabundance of nutrients is subsumed by targeting the amount of organic material in the soil mix to the type of plant. Try growing container Azaleas and Rhododendrons in pure sand versus 100% composted bark. No comparison there at all. In 100% composted bark they flourish and grow like weeds. In 100% sand, you struggle with them a lot, no matter how you water and fertilize.

My percentages are by volume, not by weight, since most of us use Scoops of material to construct a soil mix, not a scale. Honestly, while your point is correct, your question is bizarre and shows someone who thinks about the wrong details.

A grow medium is a system by which we manage air:water relationships in the rhizosphere. If it wasn't, particle size wouldn't be a consideration. Hydroponics clearly shows us that a grow medium needn't contain any organic fraction in order to produce perfectly healthy plants, and conventional container culture is much closer to growing hydroponically than it is to growing in the earth. You have concluded that groups of plants need varying amounts of organic material in the medium they are grown in. How did you arrive at that conclusion?

But my experience has been that not all plants need to occupy the bottom of all containers, and you can relax this restriction A LOT for many container plantings. That's beyond the scope of this post. Personally, I don't think you can make a statement like that as part of the discussion and then say it's beyond the scope of the discussion. While it's true anyone CAN ignore the effects that perched water (PW) has on the health of plants in plantings that support perched water, ignoring the presence of a perched water table (PWT) doesn't mean it isn't/ won't be a limiting factor. We can evade reality but not the consequences of evading reality.

BTW - Dan had a valid plant about degradation of the organic fraction of grow media and it's impact on the structure of the medium, arguably the most important consideration. As soil biota cleave hydrocarbon chains the carbon gasses off as CO2. The larger the organic fraction and/or the easier the particles are digested by soil biota (high cellulose content) the faster the medium collapses.

In all honesty, most succulents, euphorbs, houseplants, vegetables/fruits, and most acidophiles will all do very well in a mix based on a very large fraction (80%+) of pine bark without complaint.

Al

Tapla, I think you are asking the wrong question. Everything can be grown in sand or pumice, or if you grow hydroponically everything can be grown in water. I am not asking what is possible. I can grow roses in the sand, in direct sun, in Saudi Arabia, as long as I don't mind watering them four times a day and constantly preparing synthetic fertilizer. I can grow vegetables hydroponically, as long as I don't mind dedicating a chunk of time every day of my life to measuring the pH of the water and constantly adding nutrients. Do I want to make that time commitment to plants? I want to own some nice plants. I do not want the plants to own me.

I am not asking what is possible. I am asking what is the optimal growing environment for container plants of different types, if my goal is to have the plants just thrive with an absolute minimal amount of my time or attention, leaving the plant outdoors year round. I generally have been finding that if I set the organic content level to the plant, I get a result that is more vibrant with far less work. There are plants that do love high organic content, and Azaleas and Rhododendrons are just one example. Those plants will probably never be happy planted in real clay/silt soil with 5% organic content, although someone somewhere somehow figured out how to make them grow that way, maybe on a slope of a mountain. But I bet there is a forest canopy for even those plants, and plenty of organic material dropping down to constantly mulch the soil. I don't want to spend time managing anything. I want to plant those genera in the soil they thrive in and just walk away. I will make sure they get water and check in with them every few weeks to make sure they remain healthy.

I want to point out that your most versatile and successful soil mix is the 5-1-1, which by my calculation is more than 85% organic material. And you cleverly got to have your cake and eat it too, by sizing the particles in that soil mix to a size where you calculated the perched water table to be minimal. Gardengal says she never needs to worry about the organic content of her soils, and in other places says she grows everything in 5-1-1. Well of course you don't have to worry about under-utilizing organic material when you grow everything in more than 85% organic material!

But I want the experience of trying to grow everything in everything and finding the hard way what works and what does not work. And I find - for example - that if I grow a plant that likes 50% organic content in a soil mix that has 20% organic content, the plant starts to struggle, and then I have to spend time to remediate what ultimately is just a mismatch of plant type to the soil mix.

I totally understand Gardengal's approach to just use 5-1-1 for everything, and then not worry about the organic fraction of the soil. 5-1-1 gives her a way to do that. I don't understand Dan's approach to imply that plants never need more than 5% organic content in a container soil mix. If you do that by putting native soil in the container, the plants die of root rot almost certainly. If you do that by adding 5% organic material to pumice or appropriately sized container sand, you won't have a perched water table, but you will be spending more time than I want to spend fertilizing the plant and watering the plant, at least for anything other than a Cactus or Euphorbia.

At the end of this journey, maybe I will end up like Gardengal and just use 5-1-1 for everything, and save myself the hassle of worrying about these issues. I am still in learning mode and I do enjoy experimenting with soil mixes, as it gives me a better sense of what makes particular plants struggle or thrive.

Now, some of you ask why I think that some plant genera need a higher organic content. And the answer is I do not know. Maybe it has to do with the CEC of the soil. Maybe it has to do with how the soil holds onto moisture after a few days have passed. I do not understand the mechanics of exactly why each plant genera likes the amount of organic material it seems to like. It just does, and I just observe this.

A very interesting discussion.

I don't really seperate gro mixes as much. I've found that most succulents and houseplants can grow just as well as veggies, bulbs, various flowers, and herbs in a mix fairly high in organic matter. I don't find any advantage to using a few different mixes for each catagory of those plants. Microgreens and square inch gardening likes high organic for me. The orchids do like their orchid mix and probably wouldn't grow as well in the regular mix. Shrubs and trees if they are small enough that I need to nursery them get potted up with regular mix. Once they are big enough they get planted in the ground rather than continued on in containers.

Hmm. If you prefer not to have a conversation with me, you're posting to the wrong place. Telling people that they're asking the wrong questions is also somewhat impolite in a forum and not particularly welcome here. That sounds like avoidance.

I respect the point about perched water, but the fact remains that you can end up with a mix that is chemically imbalanced. Now, many container mixes use large quantities of peat, but peat is actually an organic that breaks down very slowly. That is, all "organics" aren't alike. That is, a container mix with lots of peat could make sense, but one with a lot of compost would not be smart. You don't appear to distinguish between different organics.

@daninthedirt (USDA 8b, HZ9, CentTX, Sunset z30, Cfa) I thought you were implying that we should take garden soil with 5% organic content and use it for a container mix. Your posts were ambiguous, and I apologize for being rude.

Rather than deal in abstractions, what would move this conversation forward would be you giving an actual soil mix formula that you think works well for common genera of plants that normally use higher organic content. For example: Roses, Peony, and Azalea/Rhododendron. It's not helpful to have you point out the organic content of native soil is 5%. That's right. But the discussion is about container soils. Show how you actually apply your ideas to container soil mixes.

With the exception of my cacti and succulents - indoor plants that only summer outside - I use the 5-1-1 mix for ALL my containers - annuals, veggies, fruits, a few perennials, lots of clematis and a bunch of shrubs and trees. And I have been ever since being introduced to it some 25 years ago. I can say without reservation that this potting mix works equally well for anything I grow in it. And with a regular watering and fertilizing regime, all the plants thrive.

If you consider bark or peat to be organic matter, then yes, this a pretty "organic heavy" mix. But they are very durable organics (composted bark fines and peat) and any degradation before an annual or bi-annual repotting is minimal. It is not like I am adding compost or something equally as rapidly degradable.

You will need to do a lot of persuading to convince me I need to use different mixes for different plants when 25 years of successful container growing experience has proven otherwise. It is overly and unnecessarily complicating and IMO, a bit nit-picky!!

btw, I never amend inground garden soil for different plant types........why would I do so for containerized plants?

@gardengal48 (PNW Z8/9) I have nothing bad to say about 5-1-1 mix. I never said that using an organic-saturated soil mix in a container was bad. I also never said that we should use different soil mixes for different genera of plants. What I was trying to say is that different genera of plants seem to thrive in different levels of organic content, and as I said in my response to Tapla, I do not really know the details of why they respond to the level of organic matter that they respond to.

The easiest way to see this is to do side-by-side testing of the same plant species in soils with greatly differing organic content. Azalea / Rhododendrons are hard enough to grow in containers long-term as it is. But in heavily organic soil - especially composted bark - they immediately pick up and thrive. Try growing them in pure sand, or in soil that is 70% sand and 30% organic. They simply fail to thrive as well.

Each genera seems to have some natural environment in which it evolved, and in that natural environment, there is some amount of organic material. I am just trying to discover what that requirement is. I totally understand that you want to spend your time growing and enjoying plants, and you want to spend no time understanding the issue I highlighted. I may come around to your point of view.

You missed my point completely. And honestly, I really do not want to spend any more time repeating myself. 25 years of doing this says IT DOESN'T MAKE ANY DIFFERENCE!

@gardengal48 (PNW Z8/9) I think it is you who is missing my point. You have no test for a plant that does best with at least 50% organic content - and would suffer in a soil mix with 20% organic content - because by your own admission, all of your plantings are in a soil mix that has 85% organic content. I understand you have a different opinion about the issue. That's far from missing your point.

I'm not sure a lot of home gardeners test many container soils against each other by organic content. General ratios for mixes or often enough just doing it by eye, sure. But not as specific as you seem to be going westes. I've seen a lot of folks use or comment on soil testing for other things, but almost never hear of folks doing burn tests on the regular to check for organic content percentage.

I would say it is quite impossible to make a generalization about a plant needing or thriving in x-percentage of organic matter when organic matter can vary so drastically in particle size, water retention, aeration, ph, rate of decomposition... 80% pine bark is a lot different than 80% compost, 80% peat, 80% rice hulls, ground corn cobs, ground walnut shells, earthworm castings, coir, sawdust, etc. It isn't the percentage of organic matter that is important in a potting mix but rather the attributes and properties each component provides (whether it be an organic component or inorganic one).

Rodney

It can also be said that since pumice, rock, sand, clay, perlite, ect are all organic rather than synthethic that mixes containg those orgainic things could be considered 100% organic material. Many gardeners are using 100% organic mixes with the organic components varying from the more stable ones like rock to the more quickly breaking down or compostable ones like various plant bits or animal products/byproducts. If someone mixed in something manmade like styrofoam pellets or water beads, then the organic percentage would drop.

@beesneeds Let's be honest. 98% of home gardeners make their "soil mixes" using three ingredients:

1. Miracle-Gro Potting Soil (may be as high as 90% organic)
2. Miracle-Gro Cactus Mix (somewhere around 50% to 70% organic)
3. Miracle-Gro Perlite (obviously 100% inorganic)

If you have a succulent that does not like wet feet, your "mix" is 50% of 2) and 50% of 3). If you have a Peony, it's 50% of 1) and 50% of 2). In other words, gardeners start with a base that is very high in organic material, and they just guess at adding inorganic material in order to water down the organic percentage by adding perlite to the mix. People are very much engaging in a similar activity to what this thread discusses, but they are doing so at a level of pure intuition and experience, not based on any science or precise calculation.

Enter Tapla's "gritty mix" and 5-1-1 soil mixes. Tapla has given the community a rare gift. If you read his many posts on soil mixes, in effect he is teaching soil science at a level that students only get to experience in a Master's or PhD program. You don't read the topics he has discussed on gardening blogs. Having studied these things for years now, and experimented around these principles, I now have spreadsheets to calculate organic versus inorganic percentages of many soil mixes I have constructed. I have spreadsheets I created around particle sizes that I use to evaluate any vendor's sieve analysis of their inorganic materials.

What I realized at some point is that particular genera of plants were just doing better in particular percentages of organic content, no matter what specific materials I used to make the soil mix. All of those soil mixes used larger particle sizes, so it was not mainly about particle size.

Reading the responses in this thread, I realize that many here are either starting with commercial mixes that are mostly organic, or using Tapla's 5-1-1 to construct their own organic mix that has better container-science discipline about particle sizes. Apparently, I am one of the few who has played around with varying the percentage of organic material in soil mixes in a fairly extreme way. So I may just be talking to myself.

@theforgottenone1013 (SE MI zone 5b/6a) Do you have an article that discusses the different attributes of different organic materials? I get most of my organic material from the same places so I can calibrate around the behavior of one composted bark and one peat moss. That's hard enough as it is.

While the point you make is interesting, you turn the subject into a 10-variable experiment that makes it impossible for anyone except a PhD working in an industrial lab to calculate anything. It does not need to be that difficult. I don't need to get 20 types of organic material and make the experiment so complicated it becomes worthless. It does not take a rocket scientist to realize quickly that some genera thrive without much attention in container soils with higher organic content and struggle even with constant attention in highly inorganic container soils. Just try growing the same species in four types of soil that go from 20% organic to 80% organic, and you can see the trends pretty clearly.

@beesneeds No no and no. In soil science the word "organic" means something that came from a once-living thing that contains CARBON. Full stop.

Pumice, rock, sand, clay, and perlite are all geological substrates that are comprised of one or more minerals, or in the case of perlite a volcanic glass. None of these are carbon sources. They are all inorganic.

This conversation is hard enough as it is. Please don't create chaos around the meaning of words.

Goodness, I'm going to hazard a guess that I'm likely amongst the too uneducated, too inexperienced, or perhaps too common of gardeners to particpate further in this conversation. I will leave others to it then.

@beesneeds If it makes you feel better: when I was starting out in the Container forum here I was constantly inverting the meaning of organic and inorganic. All of the regulars here just hammered this into me, and part of my learning curve and reason for wanting to make my own soil mixes from individual ingredients is so that I could have a very clear understanding of what materials are organic and which ones are inorganic.

westes,

I don't know if you can help yourself not doing so, but to encourage discussion, one doesn't need to be pedantic or obnoxious. Just a thought.

@cactusmcharris, interior BC Z4/5 I accept your point and I need to practice that.

That said, if you enter 90% of the threads on this website - 99.9% of which have no participation by me - some of the same people responding here get in arguments with nearly everyone in the thread. I feel like I am playing defense. It is very difficult when you want to make a slightly technical point and try to develop a better understanding, but you often run into common social media problems. People in threads rarely work together to develop common understandings. If you think you have a point to make, you have to stand up to defend your facts. How do you defend your points to people who have more experience than you without being pedantic? I am not saying that is impossible. I am saying that requires some serious political talent.

' If you think you have a point to make, you have to stand up to defend your facts. '. There it is right there - maybe you don't.

westes, I know the difference. I'm just not up for pontificating from someone that feels 98% of the gardening population is exclusive to miracle grow products and can't take a joke about rocks, yet hasn't even grown a pepper in a pot or learned to not order from nurseries of poor repute. I get it that as a newer gardener you have excitement about things you know. But by your commentary it seems likely you aren't going to be interested in the things I know. And by you poor assumptions it isn't worth further participation in the thread topic.

@beesneeds If you were making a joke that rocks are organic, then I really apologize because I totally missed that and thought you were serious.

I would say I am a very unbalanced gardener, who knows extremely large amounts about some narrow topics (i.e., particle sizes in container soils, succulents), but lacks the very broad and comprehensive nursery industry experience that someone like GardenGal has. When raising a question about something I have zero knowledge about, I very much value the education offered to me by anyone with experience. When I raise a question about something that I have studied intensively, experimented around intensively, and grown real plants for years in harsh conditions, I want to be able to defend my ideas.

In every one of these threads on Gardenweb - not just threads started by me - any person advocating a new or unusual idea gets attacked. It is a very harsh environment. I will hopefully learn to make my points in a less obnoxious way.