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Volcanic Soil for Midwest?

McGregor, IA(Zone 4b)

I hear that the volcanic soil of the PNW is the reason irises can grow so well in such a rainy climate. I would love some for my Iowa Clay. Do you think some kind of mineral/rock chips/ (available locally) would add a similar consistency?

Anne Arundel,, MD(Zone 7b)

Consistency of your soil is very hard to change in terms of sand/ clay. Many warn that sand plus clay makes concrete. Clay plus rock chips would make sticky rock chips.
But if the minerals are what help the iris then some mineral supplement may help. Clay usually holds more minerals than sandy soil though.

Everett, WA(Zone 8a)

>> Many warn that sand plus clay makes concrete.

I think that until you mix clay at least 50-50 with compost or other organic matter, nothing will help it.

However, I think that sand or bark chunks or smallish wood chips CAN help clay, as long as you also add at least 25-30% compost. I think of it as providing enough mechanical structure to let water out and air in while waiting for your budget to allow you to buy enough compost.

(Or for you to scrounge enough leaves and clippings from neighbors.)

I want to make as many raised beds as I can, as soon as I can, so I try to stretch any compost that I buy as far as it will go. Or farther.

At least once SOMETHING will grow in it, each year I add some roots to the soil and stems and leaves to the compost heap.

But I still excavate clay faster than I accumulate compost.


McGregor, IA(Zone 4b)

Rick, you must not be in the volcanic soil section of Washington? Compost is definately most important. I have a lot of available compost material and I have been adding it over the years to various beds. I can sure tell the difference in soil texture.

Everett, WA(Zone 8a)

>> Rick, you must not be in the volcanic soil section of Washington?

It's more like I'm in the over-developed and bulldozer-scalped part of WA. North of Seattle, south of Everett - not city, but urbanized. My little (rented) plot in a manufactured home park was buldozed years ago and barely topuched since. Condo-making bulldozers are all around us, and asphalt or concrete most other places.

It might have had anything at all on top before the Bulldozers Came (years before BC?), I don't know. But I'm downstream from many mountains, and perhaps all the clay washed down over us as the glaciers retreated. I would settle for a little silt or sand or grit mixed in - almost anything - sandy subsoil would be kissed - SHEEZE!

All I really know is my yard: no topsoil or subsoil, just clay and landscape pebbles for 4-8" depth, then even heavier clay and bigger rocks as far down as I've burrowed. Almost no "perk" and it must be anearobic when at all wet.

My DSO lives near Bend - in the high Oregon desert, I've heard it called, though it does occasionally rain and snow there. Fairly cold snowy winter, very hot dry sunny summer.

The soil there is like an advertisement for fast-draining Turface or porous perlite plus young volcanic rock dust: not just volcanic, but gritty and porous volcanic. For many purposes, it drains TOO fast and holds to LITTLE water.

Nearby is something called "tuff" which I think is like fushed volcanic ash or pumice. Decomposing tuff seems like a dream soil amnedment, gut I would want to grow in a dry climate in 100% porous grit.

Any way, her soil has sandy to gritty to fine gravel texture, and the grains often look porous like it was once molten-and-gassy. Very little clay, silt, or organic matter.

I would LOVE to mix one part of her soil into 2-3 parts of my soil to make mine DRAIN(and vice-versa to make hers RETAIN more water and dissolved minerals).

Swapping several cubic yards would help both yards a lot.

But I do prefer clay (which can be fixed with enough compost and grit and bark) to sandy or very alkaline soil or muck in lowlying land that has nowhere to drain down to.


McGregor, IA(Zone 4b)

I think a swap sounds great! Why don't you start with container sized portions to start? (Hey, bet you can't guess what your Christmas present is going to be this year...;>)

Everett, WA(Zone 8a)

I would be thrilled to get a Chrstmas present of fast-draining soil!

Time to invent teleportation, for sure. That or anti-gravity or levitation. I could use any of those to turn over soil: wave my hands to levitate the top 6-12" of soil several feet into the air, then drop it to crumble and tumble. Cheaper than plowing or roto-tilling!

My budget for compost has been a point of some debate with my DSO. She doesn't really give me a very hard time, but ...

I had 4 yards of tosoil dropped off once upon a time, and the driver came up to the door for a check, but Becky answered the door. To amuse the driver and tease me, she ranted about "how COULD you spend $100 dollars for DIRT!!!"

I know the driver went away smiling and shaking his head thinking "He's in trouble now, ha ha!", but I got a wink along with the teasing.

On the other hand, hints about "I think I need to get $50 or $75 worth of compost" don't receive any encouragement. Oh, well, time to spend now and regret later.


Kalispell, MT(Zone 4b)

Come on Corey build raised beds and all drains well. It only takes 100 hours per cubic yard of raised bed. Now think of the fun you would have shoveling manure, hauling compost, cracking the whip on your significant other to get them to build your pyramid or raised bed. I have been happy with gravity ever since in my glacial till clay based garden.

Thumbnail by Soferdig
Everett, WA(Zone 8a)

>> It only takes 100 hours per cubic yard of raised bed.
>> Now think of the fun you would have shoveling manure, hauling compost,

Yes, yes and yes. For sure! If only. I wish.

>> cracking the whip on your significant other

As if! Yeah, right. Not in this lifetime. It might be good for a laugh if I tried, but then she would feel justified cracking a whip at me, and I KNOW which of us is more dominant. By a wide margin. She's mellowed out over the decades but still has teeth and claws. She's a real hot pepper, Habanero or even Ghost Viper.

The cat and I compete for who bosses who - I win most of the time. But we both know who the Top Dog is.

P.S. I did go to the closest dirt yard last weekend, past time to buy the compost no matter how feeble and overpriced. But YUCK. Nasty dry stuff whose only organic matter seemed to be dry sawdust. Zero smell: no 'soil' smell nor 'ammonia' smell nor manure smell. No nuttin'.

At $40/yard delivered! I'm going to check out other dirt yards even if delivery is more: "compost" with no compost in it is no bargain at any price. Maybe I can find a pile of sawdust.

Amusingly, the dirt-yard-guy must have seen my eyebrows when he pointed out which pile was their "compost".
"We call it 'mulch'" was his comment.

FFFPPPTTT. It might have had some evidence of anything worthwhile in it if it had been moist, but maybe not.

I can haul bags of "steer manure compost" from Home Depot, in my trunk, as cheaply, and it HAS some value beyond sawdust.


Kalispell, MT(Zone 4b)

I started all of my raised beds with Mushroom Compost (here free horse stall cleanings) and added cow manure 1 to 1 and let the horse, cow, sawdust, and urine compost for 1 year. After the one year wait I added 1 part fine clay (glacier till) to the compost, with rocks removed and mixed it to about 2 to 3 feet and "YAHOO" (cowboy talk for SKOOKUM = alaska talk for the best)! I am always happy to shovel, mix and create a world of beautiful soil.

Everett, WA(Zone 8a)

>> free horse stall cleanings

All that sounds really yummy to me. Even your "clay" sounds good: mineral micronutrients. I should research what "Seattle clay" comes from and is composed of: sediment? glaciers?

Too bad I can't haul home all the BS generated by our managers and customers and compost that!


Kalispell, MT(Zone 4b)

Seattle clay is MUCH different than ours. It is very depleted of many of the ions (minerals) that we have here. Due to the rain and moisture most soluble minerals (iron, magnesium, selenium, potassium, and many more) are washed out of your clay. Though they still do exist but not at the level of our less washed soils. The advantage in your soils though is that the lime is washed out and these salts cause alkalinity here. All of my water is rich in lime so it is difficult to maintain acidity without plant acids found in compost

Everett, WA(Zone 8a)

Good point. I totally believe that anything soluble was leached out of Seattle soil eons ago. I think I'll use more Miracle-Gro for its minerals and micronutrients. (But five times as much compost is what I need more than anything.)

In fact I think that when I do manage to create a well-draining layer on top of my soil, clay is rapidly washed out of the top and into the deeper layers (elluviation / illuviation, I believe it's called).

However, then the organic conent in the top layers is digested, and that reverts to heavy gunk all too soon.

I DROOL with envy every time you post about how much plant matter you compost and cycle back into your beds each year.


Glenwood Springs, CO(Zone 5b)


Yes, you can mix clay, sand, peatmoss, (If you don't have acid soil already) and compost to make an excellent soil.

Dig down 18"-24" and pile all that nasty clay up in a pile next to the hole. Run it through a strainer like the one pictured below to get out the rocks & PULVERIZE the clay. Mix by shovelfull in the approximate ratio; Coarse Sand 40%, Clay 30%, Peat Moss 15% & Compost 15%. Make sure all the ingredients are dry & you only add back to the hole no more than 6" at a time so you can really mix it well with a rototiller.

Add some Azomite or green sand along with some high quality organic fertilizer like Dr. Earth that contains bacteria & michorizae.

It is not so much what you do as opposed to how you do it! You wouldn't add your wet ingredients to a cake mix unless they were well mixed and sifted???


PS: I love the soil in my new 24'X10' terraced bed. All 76,000 pounds of dirt was moved and mixed by hand because I couldnt get a trackhoe in there! I will be planting my 40 new tall bearded iris this weekend.

Thumbnail by Pewjumper
Kalispell, MT(Zone 4b)

Corey I this year will fill 2 bins with the collection of organics that my garden produces. I am so glad I have my debris loader to chip shred and suck up the yards and yards of carbon I accumulate. This year I have dropped many Doug firs and plan to use the millions of cones in the compost pile. They last longer than wood in soil structure. We have a severe attack this year on the fir from a moth larvae from the extremly great spring and summer. There is an excess of new growth that feeds this tussock moth and the trees are being destroyed by them here. They won't die but they are being denuded by this saprophyte bugger. Therefore I will take out the weak ones because I am making a monoculture of the many Ponderosa Pines I have and they don't like competition from faster growing fir.

Everett, WA(Zone 8a)

>> use the millions of cones in the compost pile. They last longer than wood in soil structure.

I believe it. I guess they don't sprout and turn into seedlings, or does that happen in the compost heap, and the seedlings get digested?

Do you happen to know whether shredded pine cones or shredded pine bark lasts longer in soil? I don't immediatly see whether the cones are suberized, but from their feel, they either have that or silicon dioxide.

I never ised to put them in my tiny pile - I assumed they wouldn't break down. I guess the trick is to mow them several times and sweep that into the pile.


McGregor, IA(Zone 4b)

I am still digging out intact pine cones after 2 years of adding them to the soil. They probably break down eventually.

Kalispell, MT(Zone 4b)

The fact that they last a long time before breaking down is the structure that allows worms to penetrate and ingest the carbon material in the compost. Every seed pod is a haven and freeway for worm travel. Yes some near the surface start but I am continuallly transplanting ponderosa on my 3 acres. I need a mixed colony of trees to make healthy monoculture.

Anne Arundel,, MD(Zone 7b)

"reverts to heavy gunk"
Then I suggest trying to add chunkier stuf such as the whole pine cones (if you have them), corn stalks or sunflower stems in chunks, bark chunks, broken sticks rather than too finely chipped...It takes a darn big chipper to make chunky wood chips.

Everett, WA(Zone 8a)

>>. "reverts to heavy gunk"
>> Then I suggest trying to add chunkier stuf such as the whole pine cones ... bark chunks, broken sticks rather than too finely chipped...

Exactly! Pine bark mulch and very coarse sand (grit) are good and I've been using them.

I have some semi-compoisted sticks and tough stems coming along, noit by plan, but becuase the lawn mower blade needs sharpening and the darn things are SLOW to compost.

But they will help provide "mechanical" structure to the clay ... my first 2 years of compost add up to about 2-3 cubic feet.

To improve clay, I think both are needed: organic-matter-compost to add carbon to the clay, get some living things going, and make the pudding-texture clay more soil-textured. Then, also, something coarse and soemthing very coarse, to "prop up" the gunk and maintain some air channels and drainage, while the OM in the soil is gardually being increased.

if I could drop about 12 or 18 inches of finished compost onto every bed I own, and turn it under, that would help a lot! However, it's more like a few inches per year of finished compost, so you're right: I also ned the coarse stuff.

Pine bark mulch is a wonderfull thing!


Glenwood Springs, CO(Zone 5b)

Ummm, adding organics too clay is not nescessarily the answer. People all over the world still make bricks by mixing clay and straw.

The ammount of organics needed is considerable, (I used 30%) and when the organics break down you still have clay. Refer to my post of July 26.


Virginia Beach, VA

Make sense " When the organics breaks down then you have clay!!!


Everett, WA(Zone 8a)


I agree with what you said in Post #8717254 (July 26). 40% sand would be a great thing, and certainly a permanent improvement. Using that much of something coarse may be needed to get the best results if the soil itslef is pure clay

Indeed, only things I've bought entire cubic yards of have been coarse sand (grit) and pine bark mulch, thinking they gave the most long-lasting improvement per buck.. But over my whole yard, 12-18" deep, that might be only 1% to 4%. Money and the time and ability to haul it are limiting!

I think that lots of finely divided organic matter is also necessary to make clay into soil. Until that happens, clay is sticky, which is what lets it glue straw or other fibers together. So I'll be buying bags of manure-compost (or yards, if I find a better source) for some years. The amount of compost I make in my yard is tiny: not much to feed it with.

My way of looking at it is that there are two major parts in soil. One part is "fine", let's say smaller than 1mm in the largest dimenision. Clay, silt, tiny organics, loam, peat, fine sawdust, medium & fine sand or whatever "fine stuff" you have that is mixed together. Hopefully it will eventually have enough internal complexity and structure to form clumps or clods that have tiny internal openings, and larger openings between one clump and another. Thus maintaining aeration and drainage "all by itself". I'm still working towards enough (finely divided) compost and organic matter to make that happen.

As I look at it, "big stuff" like grit, gravel, bark or wood chips or big fibers are more like scaffolding, or the "mechanical engineering" part of soil. To work well, there has to be enough of it that the "un-clumped" parts of the fine stuff can't fill and "drown" all the voids between the coarse scaffolding. Visually, the 'scaffolding" has to rest on itself, hold itself up, and create lots of open space.

Using 40% coarse sand or grit would do that really well, in one fell swoop.

Then, the "fine stuff" can't be allowed to fill all those voids. Hopefully, it can form itself into clods 1mm to 1 inch in smallest dimensions, and the clods would be strong enough and stiff enough to form more scaffolding themseleves.

But the "crumbled" part of the fine stuff will sift down and fill voids.
And pliable clods, like clay, will squeeze themsleves into voids.
And sticky clods, like clay, will stick tightly together and shmoosh out any void spacebetween them.

So they clay itslef has to be amended (with OM and fine sand and silt).

I'm adding some of both, hoping that promoting some clumping and some scafolding works better than all one or all the other.

One reason I like pine bark is that it will last several years as "scaffolding", while gradually decomposing and feeding the soil microbes (as OM) even if I skip compositng that bed for a year.

I think you suggested 15% compost and 15% peat? If peat really is more expensive per cubic foot (expanded) than rich composted manure, then I'll stick with my plan of buying as much composted manure as I can haul and spread (and budget for). In part, I just don't like peat, not sure why. Most people love it. I like compost better for the OM, and pine bark better for the structural scaffolding.

I wish I were adding 30% of anything organic, but it's more like 3% to 10% per year, and not every bed gets something every year.

It might be smart for me to find a cheap source of sawdust for OM, wood chips and fibers for structure, and compost that with manure compost and maybe biosolids. If I were retired but could still afford it, I probably would. But I've had NASTY dry-lookin fungus when i put too much uncomposted wood in a bed, and never wnat to go there again.

Plus, I just like bark and grit and compost!


Anne Arundel,, MD(Zone 7b)

This reminds me of 'tapla' s educational posts in the houseplant foru, about soil structure, and many of your points are like his. If you haven't read his threads about potting soil, you might like to.

In limited parts of my beds, where I've gottten a really good dose of organic stuff going, I can actually see the nice crumbs formed with plenty of OM.

Kalispell, MT(Zone 4b)

I too agree with Corey. Compost is acidic and dissolves clay into rounder substance. (it is flat when seen under micro). Acids dissolve the mineral and make the powder round. Two the addition of carbonic acid (compost) feeds the microcolony of bacteria, worms, etc and soil improves. The rough carbon of slow breakdown material provides "freeways" of travel for these benificals. Hence continually adding compost greatly improves the soil. Now I use 2 parts of compost to 1 part of clay. My glacial morraine is very soil rich with this ongoing process to a depth of over 12" below the raised beds.

Everett, WA(Zone 8a)


Yes, Al = tapla clarified many things I had only worked out vaguely, corrected some impressions and turned me on to pine bark.


>> [clay] is flat when seen under micro). ..
>> feeds the microcolony of bacteria, worms, etc and soil improves.
>> The rough carbon of slow breakdown material provides "freeways" of travel

I agree with all you said. Probably fungal hyphae provide some of the rough organic 'freeways' that I think of as 'open space under the scaffolding'.

I also guess that ions from minerals and "humic acids" must bind to charged sites on sub-colloidal clay particles and either prevent them from clumpiong, or form bridges and spaces to hold them apart.

What's one step more speculative than guessing? I speculate that the reason gypsum (CaS04) is thoguht to "loosen" clay is that the multply-charged ions - positive and negative - are extra-effective at blocking or bridging charged sites on clay particles and act like wedges or anti-stick agents.

I always wnated to learn some soil scince, but the best I've found has been the oldest and least scientific. There may be modern scientific texts, but I haven't found any that are cheap and clear!

The rule that has held up best is "good soil has some of everything". Big and small particles. Clay, silt, sand, grit & organics. Big organics and fine organics. Air, water, and solids. Minerals and living things (inclduing worms, burrowing bugs, fungus and roots). Sometimes warmth and soemtimes frost heaves. Stable structure, and mobile water and air.

Like alchemy: some of everything, all the opposites in harmonious and co-operative interaction.

Greater than the sum of it's parts.

Like a civilization or a mind: it can't function if it totally lacks even one of many components, some of which are looked down on by the rest.

Soil is cosmic.


Glenwood Springs, CO(Zone 5b)

Soferdig is right that clay is flat and that is the problem, It compacts nicely. If over compacted for construction purposes particles wil slide past each other because the particles hold on to water on their surface due to the Van Der Walls force. This is one of the reasons why clay retains water and tends to exclude air.

When I am building soil here in Glenwood Springs, Colorado I find mostly a silt/clay with lots of rocks. This dirt is largely devoid of organic matter and life forms with a pH of 8.2. The mechanical seperation and breaking apart of this dirt is essential in the building and mixing of a soil with lower pH, higher organic matter that retains water & nutrients but also allows good drainage.

In my case, it has worked wonderfully, as is evidenced by the healthy plants and the exploding population of worms. I only have to water twice a week for 40 minutes with an oscillating sprinkler when temperatures are in the low 90's.

I have introduced soil bacteria and michorizae and the soil structure and ecology will improve over time.

The process is labor intensive and expensive but worth it. I have a new limited source of peat moss from a resevoir they were digging in Snowmass Village at $27.00 a cubic yard. It may even contain some fossils!


Everett, WA(Zone 8a)

>> The mechanical seperation and breaking apart of this dirt is essential in the building and mixing of a soil

I agree. I break mine up and starin out rocks with
1) steel wire shelving with ~1" rungs
2) 1/2" hardware cloth
3) 1/4" hardware cloth.

Funny thing: there are always some small "clay balls" around 1/8" - 3/8". They tned to roll down the sides of the cone of sifted dirt during tjhe second two steps. I've started to "demote" those clay balls on thery that they are "purer clay" than the rest of my dirt.

I scoop them away from the sifted piles and throw them aside, to MAYBE amend one of these years. When i tried crushing and re-sifting them, they seemed even nastier than the rest of the clay.

>> higher organic matter that retains water & nutrients but also allows good drainage.

That's my goal, also

>> I have introduced soil bacteria and michorizae

That's my next intended refinement, but have not found local sources that are inexpensive. I have some online options when I'm ready to spend money, AND do a lot of work in a few motnhs (so they stay fresh). Meanwhile, I take shovelfulls of "innoculum" from my healthiest bed and compost heap, and mix them into raw amended clay and "sick" beds.

>> The process is labor intensive and expensive but worth it.

Strongly agree!


Glenwood Springs, CO(Zone 5b)

Has anyone seen Caitlin?

She seems to have turned up missing! ;)


Kalispell, MT(Zone 4b)

Sorry been in AK working, too much! So the above I have learned and agreed. I also believe carbonic acids "carve" off the edges and make ions available to the plant as well as rounding clay to more drainable material. Hence the micro enviroment feeds off bioproduct. This then feeds up chain to worms etc to make soil "perfect". That is how compost works.

Provo, UT(Zone 5a)

i have good soil here..i live near river tons of rocks..i have good drainage..
i have done a TON of composting over the yrs.. ive reaped the benifits.. my plants are
happy campers..
question?? i add fair amount of perlite every my compost soils where mostly tropicals
go in.. (EE,bananas,gingers).. ive read alot on use of pumice..or lava rock.."cinders"..
theres "chat" on use of lava because of some "paramagmatic" benifit .. from my reading
there isnt any real science showing this..but from experience..especially "dirt doctor" who i
respect.. that there is something there...
???? thoughts???
much thanks...

Virginia Beach, VA

I too have lots of EE, bananas and other tropicals that are brought into the sun room and garage and are repotted every spring. It is a big project because I put them in large containers in the fall then are put in pots for the outside. I use mulcc, walmart potting soil and garden soil. I very seldom use perlite because of expense.


Glenwood Springs, CO(Zone 5b)


I can think of no benefit to adding pumice to your soil. Volcanic soils that have been broken down naturally are rich in minerals and generally have excellent drainage.

Since you live in Utah, you may want to try adding Azomite which is a volcanic product used to enhance soils with all the minerals and micronutrients your plants desire. It is the western answer to greensand.


Provo, UT(Zone 5a)

i think im on same way of thinking with u pewjumper with the pumice..
i have good soil here.. i make a TON of compost every yr.. :) dont we all ..:)
ive read on azomite..and theres a good source for it locally.. yea..
ive been thinking of zeolite.. i use it in my aquariums to absorb ammonia out of
tanks.. but read that its good to put on lawns .. im thinking of use on part of lawn that
faces south..and just get blasted with july/august heat..
anyone tried it on their lawns???
thanks to all....

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