Adding perlite to clay soil


Hi. I have been trying to do some research on what I should/could add to my heavy clay soil to try make more permeable. The soil is completely flooded today after a heavy downpour. I have been interested by what I have been reading about perlite and thought I'd best ask some advice before I go adding it to the soil. Is the addition of perlite a good idea to loosen heavy soil and how much do I need to add? I noticed that somebody mentioned gypsum in a previous post too but that seems like not such a good idea. A bit lost as to what to do.

Posted by: Megan Long (3 points) Megan Long
Posted: August 28, 2013

Katherine commented,
Hi Megan, I'm wondering the same thing. Did you end up trying the perlite?
almost 2 years ago.


The problem with modifying heavy clay is the volume of material you have to add. Ideally, clay should only be about 20% of your soil mix, the rest being 35% silt, 35% sand and 10% organics. Heavy clay soil, or soil that's at least 50% clay needs a bit of math to be properly amended Have your soil tested and the report will list what percentage of each soil type your heavy clay has, the better companies will even tell you what amendments your soil needs. Figure out how many cubic feet of sand/ silt/ organic per cubic yard you need then till in the organics first, silt then sand last.
This can be a pretty expensive and labor-intensive project so many people choose to make do by adding in loads of organics to take the place of sand and silt. The organics will hold the smaller water particles that your plants need and form air pockets in the clay.The drainage problem will still be there but much improved. Others choose to use raised beds which cost more than the organics but less than completely overhauling your soil structure and have the added benefit of not disappearing into the deep clay after a few years.
Like any powder or liquid soil amendment gypsum leeches out of the soil quickly and may disrupt your beneficial soil microbes. It's a quick fix that comes with a price By putting it on here for everyone to see maybe someone will find something similar that's more sustainable.

Posted by: J.D. Archer (31 points) J.D. Archer
Posted: August 29, 2013

Perlite will float away.

What you need is mulch and more mulch. Call local tree trimmers to find out who will deliver a truckload for free.

Also see https://www.plantvillage.com/posts/12...

Posted by: Tanya in the Garden (128 points) Tanya in the Garden
Posted: August 29, 2013

I agree with Tanya - we added a lot of mulch to our garden in TN and the results were magnificent.

I wrote about it here: http://theprepperproject.com/the-pros...

Also, check this out:


That shows a photo of what happened to poor sand after a few months of piling up organic matter. You're lucky to have clay instead - it really holds the nutrients once you get it in shape.

Posted by: David Goodman (67 points) David Goodman
Posted: September 3, 2013

Adding mulch to sand is a whole different kettle of fish to adding it to clay. With sand, it drains; with clay, it doesn't. You can add mulch and compost by the ton, and it will mostly just disappear. There are no miracles.

If you have a chunk of heavy clay land and dig a hole in part of it to make a garden, fill it with mulch and sand, what have you got? You've got a hole surrounded by clay, like a full bathtub sitting in the ocean. It's still not going to drain because the water has to go SOMEWHERE. The only exception might be if you've got some slope, and terrace it so you do have some natural drainage. And it's still going to be a lot of work.

I would keep it simple: build some raised beds with decent soil (check it before you buy it to make sure they're not selling you more of what you've already got) and compost. If it seems to drain too fast, add up to 1/5th (by volume) of your natural clay to it and mix it in well. Clay does have benefits: it retains moisture and contains many important minerals.

Posted by: FussyOldHen (16 points) FussyOldHen
Posted: September 5, 2013

David Goodman commented,
"Adding mulch to sand is a whole different kettle of fish to adding it to clay." Of course, that's why I gave an example on clay as well.

Our clay in Tennessee was hard, thick, and rocky. Miserable stuff, though mineral rich.

After a year of piling mulch and organic matter on top of it, it loosened up and was much better for planting. Worms worked the soil, tunneling up and down through the mulch and clay layers, mixing the organic matter into the clay and letting it breathe.

over 7 years ago.

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