The impossible ideal soil thread

General Gardening
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The long and short of it:

  1. What is the best soil possible, and what factors are involved?
  2. Does the best soil vary by climate?
  3. What methods can gardeners use to create similar soils, and should they?
  4. What methods of creating an ideal soil are scalable from garden to orchard to agriculture?

Now, context is of course important. The target species of plants matter, as do things like local disease pressure, water pH, etc. That being said, I’d say the goal here is the answer the above questions at the most general level: for the majority of garden, orchard, and farm plants, under typical growing conditions, and in most areas of the US, the EU, or similar places.

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it’s probably local too. we don’t get a lot of rain so drainage isn’t much an issue here, water retaining is a bit better. in a rainy place well draining soil matters a lot more. and then, trees and annual veggies will want different things I think, for the most part.

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Right off the bat I’ll give three examples of what I have seen described as the most fertile soils, the best soils, or the most ideal soils out there.

  1. Volcanic soil
    Typically in Mediterranean or tropical climates (parts of Italy, Hawaii), but sometimes in the subtropics and temperate zones (eg. parts Japan and New Zealand).

Volcanic soil is touted as superior due to several different factors. The soils are geologically extremely young, so they are highly chemically active, both being still rapidly weathering and having a high cation exchange capacity. Additionally, the soils are very “light.” Relatively large particle size, combined with a high proportion of glasses and similar materials and an extremely high amount of porosity, mean that the soils are physically light, drain very quickly, but still hold a lot of water.

  1. Chernozem
    Some areas of the US and Canada, and vast areas in Ukraine and Russia, with scattered smaller areas Patagonia, China, etc. Always in cold temperate zones.

Chernozem (Russian, чернозем, literally just meaning “black soil”) has the highest level of organic matter of any commonly occurring soil outside of wetlands and certain alpine environments. These soils have very high nutrient loading and availability, can hold enormous amounts of water, and are typically extremely deep. They are not, however, especially well-drained, and can remain water-logged for long periods of time.

  1. Juniper Level Botanic Garden

A special mention. Juniper Level Botanic Garden, just outside of Raleigh, NC, is an interesting case study in soil conditioning: they grow slightly over 21,000 species and varieties of plants, all using the exact same soil mixture and pH. That mixture is 50% permatill (expanded slate), 25% compost, 25% native soil, kept at a pH of 6.2 to 6.5. They, in the same soil, are growing orchids, agaves, proteas, ericaceous plants, bananas, cacti, and pitcher plants, among others.

Some food for thought.

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For fruit trees drainage is the most important soil feature. My current soil will drain 2 inches per hour 24/7/365. Less than 2 inches a day is bad even in a dry climate. Drainage is way more important than water or nutrient holding capacity for fruit trees. But that can vary with climate and irrigation capability.

For garden crops I’d rather have a stronger soil. Stronger meaning holds more water and nutrients. This is particularly important for crops like corn grown without irrigation.

A soil that’s too strong is bad for fruit trees. It causes excessive vigor, sometimes poor fruit set, and lower fruit quality. Mark our peach grower in eastern KS has a strong soil and fights excessive vigor non stop. It also causes low brix during rainy periods.

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These soils form a large part of the US corn belt. The soils formed from wind blown loess and glacial till from the last ice age. The high water holding capacity is important for field crops like corn, soybeans, small grains, and forage crops like alfalfa. This is the largest most productive area of exceptional soils in the world.

Those soils will work for fruit crops but better drained lighter soils would be even better.

The largest areas of soils good for fruit trees in the US are on the plains from Colorado and Nebraska down thru western Texas. The problem is that area has poor weather for fruit crops. Lots of loamy and sandy loam soils in that area. If California had these soils it would be even better than it is for fruit.

Better yet if the plains suddenly had CA weather I’d be buying every acre I could of the best loamy soils in the plains.

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That’s kinda the thing with chernozem though, it can only exist in a specific, and very narrow, climatic belt. Even if you hauled dump trucks of it into the central valley, that soil would steadily lose organic matter until it resembled the rest of the soil in California. Soil organic carbon is mostly an equilibrium between rate of addition and rate of degradation. Wetlands severely restrict degradation, so they accumulate organic matter, whereas moist tropical rainforests have insanely high rates of degradation, so the soil is almost pure mineral substrate. Prairies exist in a sweet spot where there is a highly productive ecosystem (grasslands) sitting in an area that is moderately dry, especially during the summer, and has fairly low average soil temperatures, both things that slow degradation (the short growing season + long growing days probably helps tip that equilibrium further as well).

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The major issue with CA soils isn’t a lack of organic matter. It’s that they’re old soils that have developed hardpans. Those hardpans need D10 Cats with big rippers to loosen up the soil. With irrigation and fertilizer about all the soil needs to do is hold some water.

In the corn belt organic matter does matter. No irrigation so water holding capacity and tilth are important.

I’m growing the best fruit I’ve ever eaten on a clay loam soil with about 1% organic matter. More OM won’t help produce better fruit and might hurt.

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Like everything else in life, it depends. That’s another way to say that there is no such thing as the ideal soil.

There is such a thing as the ideal soil for a particular plant and a particular environment. All my potting mixes are very heavy on sand because we get tons of winds and I need the weight. What could be your ideal fluffy potting soil would be horrendous here.

Some plants like sandy soil, some like extremely organic soils. Some plants love lots of water, some plants will rot in the same conditions. What is ideal for one is not ideal for the other.

Then there is the holistic view of soil as an eco system; where you are and where you want the soil to be. I mulch with a ton of green woodchips (sub 2" branch stuff) which decomposes and builds up the soil as an ecosystem. I also don’t have to worry a whole lot about the cation exchange capacity of my soil because I regularly fertilize as needed, so nutritional reserves provided by the ideal soil is less of a concern.

Lastly the ideal soil can get out of whack in half a season. Just the PH can move and make all those nutrients there unavailable to the plants. Somebody that monitors substandard soil may end up with better plants than somebody who just thinks their ideal soil is doing everything when in fact something is missing.

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That’s a good point. I suspect, though, that “strong” might be combining a few different things. Soil permeability, CEC, pH buffering, field capacity, aeration, etc are all different things, even though we’d probably identify all of them with a strong soil.

I think a bit reason why they get lumped together is that, aside from the sand to clay spectrum, gardeners are mostly concerned with their total soil organic matter, and total organic matter will move all of those soil qualities to a pretty much set degree, and things that might alter only certain things, such as adding large quantities of newly weathered rock or highly aerated non biodegradable materials, aren’t the kinds of things gardeners do outside of the context of potting mixes.

Which is why I made mention of volcanic soils and the stuff Juniper Level does.

Hmm, not sure that I agree. Soil is not just a medium for water and fertilizer salts. Air and microbial activity are probably more important than water and fertilizer. Organic matter is the standard method gardeners use to improve soil aeration, but there are other ways as well.

Similarly, more organic matter does not necessarily equate to more nutrients and higher plant vigor (which, I agree, can be bad for fruiting trees and vines), and, perhaps more crucially, better aeration, CEC, pH buffering, etc, are also not necessarily going to mean higher nutrient levels and the associated vigor, but those higher values can very easily still increase overall plant health and or resilience. Or, if nothing else, enable a broader diversity of plants.

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Hydroponics proves that about all you need for soil is something for the roots to occupy. What do they use, mineral wool, sand, coir?

I grew up in love with the black soils in the Midwest. Many gardeners are obsessed with organic matter. The more the better. My current situation proves to me that it’s not needed to grow great fruit.

I’d still love to own a thousand acres of Muscatine silt loam, considered by many the best soil in the corn belt.

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Sandy silt loam is the best overall garden soil. I’m fortunate to have this type soil for my garden. It only covers about an acre of my land. Since I’m in the rainy southeast, organic matter has to be added via cover crops and manure. To give examples, we had a very rainy summer so far producing tomatoes that are up to 50% larger than normal for a given variety. My corn has produced much larger ears than normal. The combination of excellent soil with fertilizer and abundant water makes gardening dramatically more productive.

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Sure, but I think that was implicit in my original post. The issue then becomes, “what soil would allow one to grow a very broad array of desirable plants, maintain their health and productivity, and be reasonably climate-neutral and saleable.”

Part of the motivation for that question is the simple fact that people generally over-estimate how picky plants are when it comes to soil. Baldcypress grows in swamps, cacti in deserts or deep sand, and blueberries in acidic forest understories. Except, I’ve seen all three of those growing right next to each other, and doing better than they usually do in the wild, at the JC Raulston Arboretum. Baldcypresses don’t actually like waterlogged soils, they just have a very high tolerance for low oxygen level, so in the wild they have a comparative advantage growing in periodically inundated soil, blueberries need some acidity, yes, but they can handle far less acidic soils so long as there is sufficient organic matter and microbial activity, and cacti really don’t care that much so long as the soils is very fast draining and there isn’t too much organic mulch or debries touching the base of the stem.

I don’t remember if it was a Crime Pays But Botany Doesn’t video, but I remember seeing a video in the Central American cloud forests of either an agave or an aloe, don’t remember which, growing along the edge of a creek bed. How? Because it was growing in a deep volcanic soil with extremely fast drainage. Despite the nearby body of water and high rainfall, there was essentially never any standing water around the plant or waterlogging of the roots.

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Totally agree here.

I think it it partially because of the intellectual heritage of most American gardeners. We all grew up reading books by folks who gardened predominantly in the Northeast or parts of the Midwest. For them, maintaining high organic matter is relatively straightforward and probably the best way to practically and easily improve their soil structure. And since their growing seasons are short, the weather cool, and the sky cloudy, having nearly black garden soils probably does not actually come with many drawbacks like we see in other regions.

Add on a second generation of gardening writers who were active in the 60s and who gobbled up all kinds of nonsense about the inherent goodness of Life and Nature (capitalization intended), and you get a bunch of gardeners doubling down on the idea of increasing soil organic matter and microbial activity, and you get a recipe for a cultural norm of trying to reproduce the soils of the Ukraine in all the places that aren’t the Ukraine.

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Technically speaking there is no such soil. At least according to the soil textural triangle. I’d call that soil a loam. It’s in between sandy loam and silt loam. The best corn belt soils don’t have sandy in the name. They’re mostly silt loams or clay loams. Sand is basically just an inert filler in the soil. I’d rather have about 70% silt and 30% clay. Leave the sand for a playground.

But there’s absolutely nothing wrong with a loam soil. It’s a great compromise for both a garden and fruit trees. I’d love to own a thousand acres of deep loam with a water table at 3-10 ft. Deeper for trees more shallow for a garden. That would be a great setup for pecans, corn, peaches, and about anything else.

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My soil for citrus is different than the soil I use for my stone fruit. The citrus soil is very light and drains very easily. Might that soil be better for all of my fruit trees? I know that citrus does not like wet feet!

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A rapidly draining soil is good for most potted plants. But it does require more frequent irrigation. That’s the main complaint that most people have. If you miss a watering it can bite back.

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Best native soil I’ve come across has been working along Raccoon Creek and Slippery Rock Creek for streambank stabilization projects and I’d say this is what it was. If I had my garden at the time I would have been taking trunk fulls home to supplement our native coal spoil, red dog, and clay :melting_face:

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Ha!

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Im watching the new Earth documentary on BBC this week and it tells how no plant or animal etc life on earth existed until a few fungis etc lived and died and lived and died…then other things lived and died and lived and died for billions and billions of years…also many volcanic eruptions spreading nutrients all over Earth…then flooding and fires… so the scientific answer is high organic matter from many trillions of things living and dying over many many billions of years makes the best soil…and the factors involved are time and everything that happens outside of human intervention.

Good show.

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The best soils are much younger than that. The rich loess soils of the corn belt are at most 10,000 years old. Old soils in many areas are many millions of years old. Old soils are generally highly weathered, poor soils. But you could argue that all parent material of all soils is billions of years old.

The loess soils in the Midwest formed from predominantly silt sized material that blew into areas bordering the Mississippi river as the glaciers melted after the last ice age. In places the loess is 30-50ft deep. In others farther from the river it’s only 1-5ft deposited onto glacial till dropped out of melting glaciers. On the bluffs bordering the river there are deep silt soils. 50ft of silt. Not many soils anywhere else that are silt texture top to bottom.

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