vermiculite vs. perlite

What is the functional difference between perlite and vermiculite?  I'm actually a little hazy on what the vermiculite does in MM.  I thought it was supposed to help with drainage, but I also have the idea that vermiculite absorbs water, so how could it do both? Does perlite help with drainage or water retention?

I'm trying to figure out a variation of MM that I can use for general gardening with plants that like well-draining soil that doesn't stay constantly wet, like butterflyweed and sedums.  I have heavy clay, and amend it with lots of compost, but I haven't dared to add peat, vermiculite, or perlite to the clay, because I think all three of them hold water, and I don't need to hold any more water than the clay already holds.  

But I admit I'm unsure.

Guin, when I have more time I'll add to this answer.

I may yet be convinced to approach the local coffee shop for grounds.  I have a filter full every morning, and I've been putting them in my compost tumbler, but adding them right into the clay sounds like a good idea.  I won't have enough to fill my whole bed, though, without searching farther than my own kitchen. 

I did discover today while pickaxing the clay bed that under a 6-8" layer of hard packed clay is a layer of sand and gravel, so I'm heartened at that.  I don't know how deep the gravel is, but at least the bed is not 3 feet of clay!  It should drain well once I get the soil amended, and maybe I won't need any vermiculite or perlite.

I have a truckload of "premium" compost from a local nursery. I couldn't mix five different kinds for this project volume, but I have used this nursery's compost in another flower bed which is doing phenomenally, so I think it must be a good mix.

for Mel's Mix vermiculite is the preferred additive. It both absorbs water and nutrients and releases water and nutrients, When water is released, air pockets are formed which are important for the roots.

Compost, peat moss and vermiculite have good cation exchange. Perlite does not.

For clay soils, compost and more compost will help with drainage. Mixing in other organic material such as coffee grounds, straw and peat, plus planting will help. As the plant and roots die, the roots break down (compost). I converted a strip of hardpan with horse manure, leaves and a thick layer of plain wood chips. It took months for it to start to change but when it did, it was easier to work in a shovel and behold, the earthworms moved in!

For sandy soils, compost and more compost will help with water retention and nutrients.

As you can see, compost is the backbone of MM, with peat moss and vermiculite contributing to other attributes.

Great questions. 

Vermiculite is more known for its water absorption properties whereas perlite of its porosity. As stated by another Perlite does not provide CEC while vermiculite, peat moss, and compost do. How much CEC is needed? I don't know and am not going to travel that wormhole. 

Why it's preferred for SFG has already been stated. 

Perlite does not actually float to the top of soil mixes. This has been tested and proven untrue. I've tested this in my own beds, 12 years old, and the blend was unchanged from the top to 2' down to the bottom. What happens is the larger particles have air trapped inside them and become buoyant when over-saturated in water like flooding. This makes the white particles on top float and since they are white against a black or brown background they stand out looking like there is more than there is. An optical illusion.  If you measure the amount it should present the ratio that was added to the mix. Normally adding more than 30% perlite in a soil mix doesn't provide better creation benefits. Although some succulent, cactus, and cannabis growers will go up to 50%. Unless you're getting into hydroponics where perlite is used up to 100% where vermiculite is occasionally used up to 50%. 

Clay, vermiculite is a clay mineral and is not recommended to amend clay soils. Its water-holding capabilities are not helpful and its soft texture will become compacted not resolving the issue. Clay is water-bound nutrient-rich soil. Fine Perlite (-20 mesh) does effectively helps treat and loosen clay soils. We have amended thousands of acres of poor farmland and fly ash fields in Ohio to make them healthy productive fields. Adding things like manure, compost, and lime are all mutually beneficial. 

When dealing with perlite and vermiculite there is a lot of misinformation. One of the reasons I'm here. Another is I like the SFG methodology of gardening. A big topic I see people misconstrue are the particle sizes. The finer the particles the more water retention the larger the particles the more aeration. Fine grades will always have more surface area to retain more water than coarse grades. Think of a jar of marbles and a jar of bbs. There is more available air in the marbles and less available surface area whereas the bbs are the opposite. Another one is perlite does not retain water. If does in fact retain water. It's commercially used as an adsorbent and kitty litter for this exact reason. At The Perlite Institute, we are currently doing studies in agriculture and golf courses evaluating the water-holding benefits and discovering a 50% reduction in irrigation and lower fertilizer requirements adding 30% fine perlite to native soils to conserve water. 

Here are two links that may help you.

Perlite for lawns and gardens 

Water retention of perlite

If anyone ever has questions feel free to reach out to me. info@pvpind.com

If you were to substitute perlite for vermiculite, what grade would you use. Still coarse?

There's a new use for vermiculite, and if it catches on we may see a real run on the material. As it is, vermiculite is twice the price of perlite, and often not as available.

It turns out there's not much you can do when a major lithium battery storage facility catches on fire. We had (have?) one near where I am and it actively burned for a week and I think it may still be smoldering. Lithium batteries are self-oxidising, so there's a limited number of things you can do to put out the flames. But someone's come up with a new extinguishing agent that uses ... vermiculite.

Lithium fire extinguisher

markqz wrote:If you were to substitute perlite for vermiculite, what grade would you use. Still coarse?

There's a new use for vermiculite, and if it catches on we may see a real run on the material. As it is, vermiculite is twice the price of perlite, and often not as available.

It turns out there's not much you can do when a major lithium battery storage facility catches on fire. We had (have?) one near where I am and it actively burned for a week and I think it may still be smoldering. Lithium batteries are self-oxidising, so there's a limited number of things you can do to put out the flames. But someone's come up with a new extinguishing agent that uses ... vermiculite.

Lithium fire extinguisher

Mark, I will tell you what I do. I use coarse perlite for the aeration and medium vermiculite for moisture retention. Both are domestically mined. Much like the Cornell Mix formula established back in the 60's. 1/3 perlite, 1/3 vermiculite and 1/3 peat moss. This formula was the horticultural standard for nearly 30 years.  I replaced the peat moss portion with a 50/50 blend of compost and peat. It works great for me.

The reason you see vermiculite costs more than perlite is for several reasons. 1. expansion ratio- perlite expands in the furnacing to a greater degree than vermiculite. Somewhere around 12x vs 8x. 2. Density- We buy by the pound (cost per ton) and typically sell by the cu.ft. (sold by volume) so coupled with the expansion ratio perlite can be produced under 2 lbs/ cu.ft. for horticulture around 5lbs/cu.ft., medium vermiculite is closer to 8lbs/ cu.ft. and coarser varieties are around 5 lbs/cu.ft. which brings up reason 3. Coarse varieties of vermiculite are sourced from overseas mines like Africa, Brazil, Turkey, China, etc. and the raw material cost is double domestically mined perlite and medium/ fine vermiculite from Virginia and South Carolina. Perlite is a much more common mineral and is not as regulated as vermiculite. Vermiculite because of the asbestos issue of Libby, MT has to have more testing and processing due to its geological formations before it ever reaches us to be furnaced and sold to market. Perlite is much easier to mine and doesn't have the same health concerns that require all the testing and transportation. Perlite is mined in several states and Mexico.  

Vermiculite is one of the only materials approved by the IATA for packaging chemicals and batteries. This is a significant market and I've mentioned here before if you are looking for vermiculite check packaging supply companies. It's the same product. The fire extinguisher thing is interesting, I came across it about 10 years ago. They use micron and fine grades for it. Where we are also seeing growth is fireproof cements. Both perlite and vermiculite are nonreactive with most acids and counties, states, and municipalities are talking about regulating buildings to have fireproof containment systems for EVs and in parking garages. Until they make it mandatory we haven't seen all that much growth but we've had some interesting conversations with builders, architects and engineers about where we might be heading in the future.