To address the topic of your post first, you cannot "make" topsoil! You cannot make any type of soil........unless you personally have a couple of centuries or more to spare :-)

What you can do is create a soil mix using whatever appropriate ingredients are available.

Personally, I have few issues with the engineered soil mixes available locally and use them extensively in clients' gardens. But few 'garden mixes' as they are typically referred to here contain that much OM........most are only 20-30%. They tend to be fast draining and moderately moisture retentive and suited for just about any plantings - trees and shrubs, flowers beds, vegetable gardens.

I have never found a need to alter these garden soil mixes to accommodate acid lovers. Most of the mixes test out with a pH that is slightly acidic anyway and it would only be something more demanding - like blueberries - that would require additional amending.

If you wanted to create your own garden soil mix - not a task I would devote any time to personally as I doubt it has any significant advantages - then look for actual, unadulterated topsoil or screened fill and then add whatever OM or other amendments you wish in the proportions you prefer.

As an aside, please do not post or crosspost in the Ask the Yard Doctor forum. There is NO Yard Doctor - hasn't been one for years - and that forum is restricted from any members who access from GardenWeb. Which most of the serious gardeners on this website tend to do. It was never intended to be an open discussion forum so does not allow comments. To respond, one has to leave GW and reenter using the Houzz portal - a major PITA!!

@gardengal48 (PNW Z8/9) I will strive to stop using the "Ask the Yard Doctor" group. They should just remove it to prevent that mistake. If you see me use it again please ding me.

@gardengal48 (PNW Z8/9) No one here sells true Topsoil. And if they did it would not help a bit, because Topsoil A would be 40% organics and Topsoil B would be 10% organics, so you might as well just get someone to give you the actual composition of the mix and decide what you want to use for your application.

What I have available to me is either pure sandy loam - which is definitely real soil - or a frankenmix that was someone else's idea of what topsoil should be like. I choose to start with sandy loam and just add my own organics, which for my small areas is not a huge task.

This gets me back to the original question: you are okay with topsoil having 30% organic matter? In farming - as you are aware - organic matter in high-quality farm soil is rarely over 10%.

First, I don't see any particular issue with the contents of the soil in that picture you linked - twigs and bits of woody materials are perfectly fine in soil. If you don't like it for aesthetic reasons, that's up to you.

Second: since the organic part of the 'frankenmix' you mention doesn't bother me, my simple suggestion would be to buy the frankenmix and whatever closer-to-pure loam or soil without organic content and mix to your target ratio.

In more general terms - depends what you're using this for; from what I've seen here comments warning against too-high organic fraction in particular mention using it in yard to 'level' the ground. And that doesn't work well because it will subside considerably over time and not evenly and won't actually level things out (if the ground isn't level to begin with, adding compost will just make it look level to the eye temporarily).

But I think you're using this for some raised garden beds/planters? Personally, in that context, I'd be fine with a fairly high organic content; use whatever you want. Sure, the soil would settle and subside as the organic content decomposed more - but if you're going to be adding compost/soil/mulch in future years, does it matter that much? Just keep adding to taste. Note that even for compost/mulch you add later that's 100 percent organic matter, not all will decompose to nothing - and certainly not in any relevant timeframe; some will get bound up - agglomerate - with soil particles, some turns into stable organic compounds that don't decompose much, etc. This is more true of some organic compounds esp lignins than others. And if the extent to which it subsides/decomposes and hence how much you have to add each year annoys you, add more mineral soil.

There are a whole lot of caveats for specific uses/plants and I'm not advocating going for 100% OM, and it may depend on what you're planting and a host of other factors.

That said - I may be a bit of a heretic on this point here. I find that lots of plants will grow fine in a VERY organic-matter heavy mix, many will grow in 'soil' that's basically just compost. Of course, that doesn't mean it's 'optimal', I'm just saying it's not quite as bad as may sound.

Opinion only: yes, 'good agricultural soils' may typically range from 5-15% organic matter, 10% a nice round number. But your planters are not 'agricultural soil' found in a field, it's soil you're making. And I think this "good agricultural soil" mixes up a descriptive and a prescriptive - good agricultural soil is the end result of a natural process that happens to be good to plant in; that's not the same as saying you must be in that range at all times (the prescriptive part).

Put differently, my thinking is that in nature, good 'soil conditions' will tend to decompose OM to some equilibrium level (that 5-15%) that's replenished with normal plant growth. Conversely the only time "in nature" you'd find a much higher percentage of OM is in extremely bad conditions for soil life and decomposition - like a bog or muskeg where the prevailing conditions are wet and anaerobic and so the stuff can remain undecomposed for thousands of years. (And note, even there, some stuff grows - I've been in black spruce stands that are growing on pure swamp mush, the 'ground' you walk through is mostly intertwined roots; but it's not good soil for growing vegetables).

Or in practical terms: if you load up your planters with a 50-50 soil/compost mix, that compost will decompose before long, and probably to that 5-15% range - and so you probably don't need to worry about targetting that precise range to start with (unless you have other compelling reasons to), it'll end up there on its own.

Last plea: please don't use peat for your organic portion. Peat grows very slowly and just removing peat from bogs is pretty destructive of a natural habitat. (I also think peat sucks to grow in but just my opinion)

@armoured One issue is the structural stability of the soil. If I am growing vegetables in a raised bed, then I do not care that I have to constantly replenish organic materials. But what if I built an architectural mound in the middle of my property and it is now covered with groundcovers and grown-out plants? There is no easy way to insert new organic matter into the depths of that soil, to replenish what you lose. In terms of structural stability, a soil that is 90% inorganic matter - such as sandy loam - is going to be a better selection for an architectural raised mound.

The next issue is what is the optimal percentage of organic material. Philosophically, I am trying to mirror nature. In nature, it is 90% inorganic and roughly 5% to 10% organic. If you read books on soil science, the advice to farmers is to keep within those organic content ranges, and when farmers add compost it is within those guidelines. When using compost to correct fast drainage of sandy loam soils, most books I have read suggest that you can correct the water holding capacity of the soil with as little as 2% compost. The endpoint of all of this is that natural soils and soil science both reinforce the idea that a little organic material in your soil goes a long way.

Part of mirroring nature is to put most of the organic material on top of the soil, not in the soil. So for a home gardener's use, the best place to put 100% organic material is compost as a mulch. That not only holds water for the roots, but it conditions the soil and may also serve some fertilizer functions. So my formula based on the above is 90% inorganic material, roughly 10% organic material, and then 100% organic material as a mulch on top of that 90/10 soil mix.

I am not saying that is the only right formula or the best one. I am saying it is the formula that mirrors nature and has backing from science. I feel comfortable being on that team.

So, why do so many home gardeners feel that every soil they make needs to have 50% compost in it? I think the reason is commercial, not scientific. There is a huge industry of products for gardeners that likes to sell us soils that are loaded with organic materials. Those materials are easy to obtain, and importantly they have a very light weight. Shipping costs of materials are a key component of cost. So marketers of soils have every economic incentive to push these organic-rich soil products. What they don't have is good science to back most of their product claims. Then consider which product the consumer is likely to buy. The truth is 80% of home gardeners have no clue what is in the bag and have been brainwashed to believe compost is good. Compost weighs less than half of what inorganic topsoil weighs. Is the consumer going to buy the one cubic foot topsoil that weighs 90 pounds, or are they going to go for the same volume compost-rich bag that weighs 40 pounds?

So having studied the science and wanting to do things as nature does them, I believe I have to make my own topsoil because there are very few products out there that follow the 90/10 rule. It might all be unnecessary to care about this in a true raised mound situation. But if I took the time to learn any of these principles of soil and organic materials, I feel like I have to also take the time to implement those principles in how I practice things.

Structural stability as you mention is a very good reason. I'm not going to argue the science - I'd just note that farmers have incentive to minimize use of compost as a scarce resource in large areas and volumes. In other words, not practical for them to go significantly above OM ranges. The science for that is highly focussed on trade-offs. Some agriculture takes place in "soil" that is almost devoid of OM.

You're right that incentives for sellers of soil for home gardens are the reverse, and consumers seem to believe more OM is better and some overdo it. But as I outlined I don't think that's necessarily a bad (or at least terrible) ratio to use in at least some cases.

But up to you.

FWIW I think the 'mimic nature' angle is also overdone. It sounds nice but everyone uses it selectively and it often ends up being "this is the amount of pretend nature I want." That's fine too - but raised beds are not nature either. (For example)

Anyway I'm just saying everything's a compromise. If you want the 10% ratio, buy that.

I tend to think pretty much along the same lines as armoured. Although I have never bothered to evaluate the engineered soil mixes I tend to use for the exact percentage of OM they contain, neither have I found them to present any kind of a problem. Since my own soil is at a state where all I need to add is an annual mulching with compost, I use the engineered mixes a lot for clients (have also used them personally in the past). There is no significant shrinkage, no issues with drainage and no issues with any compromised plant growth. Everything grows like mad in the stuff!! Also do no fine tuning for soil pH - it is what it is and I do not alter it unless I see issues down the road. And that is very rare.

Whatever materials are involved, when applied to or used in conjunction with ground soil, it all seems to come to an appropriate equilibrium that I have no interest in trying to manipulate myself. There has never been a need for it and frankly, I have better things to do with my time. I have no interest in trying to mimic what is found in nature or replicate "good agricultural soils" - neither of these conditions exist in a cultivated home landscape so I do not find it necessary to try and duplicate these conditions with the soils.

Of course what one does or doesn't prefer or do in their own garden is up to them but in doing this for almost 30 years in a professional capacity, my experience leads me to believe that the precise amount of OM included in the engineered mix really does not make enough difference to get very concerned about.

I have very different opinions about container soils but that is a completely different topic :-)

@gardengal48 (PNW Z8/9) Set aside using topsoil for doing raised mounds or raised beds. How are you using topsoil with plantings in the garden's natural soil at ground level?

I think saying this isn't worth worrying about so much is bang on. And if these soil/compost mixes were terrible to grow in, seller probably wouldn't stay in business long.

On this shrinkage/subsidence of soil: I think it should not be an issue in most cases. The soil will physically settle some - that's obvious - but probably mostly done after the first heavy rain. After that, if the original 'compost' fraction was well composted to begin with - at most a gradual thing, and still to some limit. My wood chip and leaf piles will shrink pretty dramatically for about a year, maybe two (cold composting), by half to two-thirds - but after that it's pretty much done - what remains is pretty tough stuff.The idea that it all gets converted into 'air' is basically false - or at least false in any normal gardening timeframe, I'm not worried about twenty to a hundred years down the road. (Compost piles of 'greens' ie non-fibrous, non-woody materials might shrink more and faster, but that's not what the soil/compost mixes sold for garden are made of).

Plus on an ongoing basis whatever's being grown there will be growing/leaving root mass behind, etc, off-setting some of what's lost, and roots - alive and dead - are also pretty resistant to quick decomposing. This is basically how nature gets to its own OM content equilibrium, as I understand it. (Agricultural practices may disturb this by plowing and discing and exposing more of the soil's 'buried' OM to air and elements - separate discussion)