Willow87

I got some expanded shale last Saturday, and I have been doing some research on it. I read from a few sites that it works better than Perlite and Vermiculite. I was wondering if this is true. I put my banana plants in smaller pots and I added a layer of it at the bottom and then I mixed it in with the potting soil. I read that no matter how much water is added it will still retain 30% oxygen. I was wondering anyone else had any experiences with it. I believe it has a neutral pH.

Richard

It is popular in hydroponic applications when the plant type needs physical structure for its roots.

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Willow87

Thanks Richard. I'm thinking about using it in a flowerbed next year. I knew it looked familiar. I've seen plants at Lowe's that used the expanded shale as a growing medium.

Richard

It eventually breaks down into clay. I don't recommend it for long-term soil mixtures.

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Willow87

How long does it usually take to break down? I read from a few horticulturist that it doesn't break down like perlite and that it can be used for long term. That's the first negative thing I've seen about expanded shale. Alot of people have recommended it.

Richard

Perlite is both a naturally-occurring and human-made foam from silicate minerals. It breaks down physically (i.e., crumbles) over time into glass silicate particles.

Expanded shale is manufactured from coal mine tailings (shale) by a similar process. It is slow to break down physically, but breaks down chemically (most notably from fertilizers) into clay silts.

Straight from the factory, expanded shale is sold for about US $6 per 4 cu.ft. sack, $30 per cu.yd., or $450 per container-load (not including freight). These are the same as manufacturers' prices for Perlite. So something is clearly wrong with the high prices and high-hype levels surrounding expanded shale.

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Willow87

Ok so horticultural sand would be the only additive that would increase drainage besides organic matter? And would perlite be considered better than shale? Its so expensive to buy and i dont want to add vermiculite because its not good for soils that are already calcium rich.

Richard

Vermiculite is used in agriculture for:
(1) an ingredient when making a soil from raw materials, and typically in a fine-grained soil for seed starts or small potted plants.
(2) as a covering on newly planted seeds -- especially when surface-sown in "plug trays".
(3) a soil-less media in hydroponics.

For my clients who have fast-draining sandy soils, we mix in composted vegetative matter (at least 50%) to slow down the drainage and introduce carbon compounds into the soil. In extreme cases, we also add one ground-up brick of coir (1/2 cubic foot) per cubic yard of soil.

To improve clay soils, you need
(1) A source of acid to disassociate the clay minerals, typically ground-up sphagnum peat moss and/or humic acids.
(2) Larger grain sands, such as horticultural sand (in rock quarry jargon, it is 1/8th inch plus, 1/4 inch minus screened crushed cobble).
(3) A "sturdy" porous aggregate, such as 1/4 inch "plus" scoria or hard pumice. As a measure of the latter, if you can crush it with your foot it is not hard enough.
(4) Organic (vegetative) matter, preferably cured fine-grained compost.
(5) A small amount of worm castings or red-wriggler worms if not already present.
(6) A 3- to 4-inch thick layer of composted mulch, typically 1-inch diameter material with some fines and some longer pieces. This will provide a great environment for the worms and other beneficial critters to live in.

First of all, "perlite" and "expanded shale" should be selling for the same price per volume and a retail price of more than $3 per cu.ft. is expensive.

Second, "perlite" and "expanded shale" are different and have different uses. Perlite is a soil aerator for modest size pots and short term plantings -- you wouldn't use it in a soil for a permanently boxed tree. Expanded shale is a medium for florists, hydroponics, cymbidium orchids, some bromeliads, etc.

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Willow87

ok thanks Richard