FAQ: Perlite/Vermiculite/Coco Coir/Peat Moss

Perlite, Vermiculite, Coconut Coir, and Sphagnum Peat Moss are four grow additives which require a very clear understanding of what they are, do, and how to avoid disaster born from confusion.


What are they?

Perlite is volcanic rock that expands greatly when heated. Perlite that's sold as a soil additive has been "cooked" like popcorn, resulting in a very light, round-like product. The concave, or dents on the surface of perlite provide for improved aeration. Kind of like a bucket of golf balls will provide better aeration than a bucket of perfectly round balls of the same size. While providing for excellent aeration, perlite is very bad at water retention. Never use perlite to hold moisture.


Vermiculite is a rock that expands greatly when heated. When vermiculite is expanded it results in very tiny layers with space between each layer. Think of a stack of corrugated cardboard and looking at the cut edges. This particular structure acts like sponge in that it "soaks" in water and holds it from evaporation. While dry vermiculite does well holding air between its layers, once water is applied it then soaks in and displaces that air. Never use vermiculite to aerate the soil.


Coconut Coir are the natural fibers from the husks of coconuts. Because coir resembles strong hair-like material, it is excellent as a binding agent. Soil infused with coir is less likely to become separated or wash away when watered. Coir contains high amounts of lignin and cellulose which prevent it from decomposing or shrinking. Coir expands greatly when watered, as it typically holds more water than peat moss.


Sphagnum Peat Moss is a natural plant material harvested from large wetland bogs. When sphagnum dies and decays it is more commonly known as peat moss. (There has been a lot of debate regarding the environmental impact of harvesting peat moss. That particular discussion is best left to its own dedicated thread. For the purposes here, I'll stick to it's viability as a growing medium.) Peat moss acts like a sponge, holding 16-25 times as much water as its dry weight, depending on the species of sphagnum. While coco coir generally retains more water, peat moss releases that moisture more slowly. Peat moss is the only one of the four additives listed here which is not considered PH neutral. Peat moss tends to have a PH of 4 or 5, making it acidic. This means that gardeners who use peat moss need to consider additional steps to increase the PH so as not to harm plant growth, such as dolomite lime or chemical additives. Like coco coir, peat moss acts as an excellent binding agent.


Perlite:
Aeration – Excellent
Water Retention – Bad
PH – Neutral

Vermiculite:
Aeration – Bad
Water Retention – Excellent
PH – Neutral

Coconut Coir:
Aeration – Bad
Water Retention – Excellent
PH – Neutral

Sphagnum Peat Moss:
Aeration – Medium
Water Retention – Excellent
PH – Acidic


Knowing all of that, what should be used, how & when?

To provide real world understanding of directly comparable water retention vs aeration, I'd purchased a large quantity of all four additives. I then placed each one into its own 5-gallon bucket. Once fully soaked I let the buckets (no lids) sit inside my climate-controlled house. Here are the results.

After 1 week
Perlite: Only the bottom 1/2 retained any semblance of moisture. The top 1/2 was totally dry.
Vermiculite: Totally wet. Even the topmost layer was still very wet to the touch.
Coconut Coir: The top 1/8 inch (3.175 mm) was very slightly dry.
Sphagnum Peat Moss: The top 1/8 inch (3.175 mm) was very slightly dry.

After 2 weeks
Perlite: The entire bucket was dry.
Vermiculite: Totally wet. Even the topmost layer was still very wet to the touch.
Coconut Coir: The top 1/4 inch (6.35 mm) was somewhat dry.
Sphagnum Peat Moss: The top 1/4 inch (6.35 mm) was somewhat dry.

After 3 weeks
Vermiculite: Totally wet. Even the topmost layer was still very wet to the touch.
Coconut Coir: The top 1.25 inches (31.75 mm) was dry.
Sphagnum Peat Moss: The top 1 inch (25.4 mm) was dry.

NOTE: due to the fibrous nature of coir & moss, I suspect the increased rate of water loss was due to capillary action. In essence, the top dry fibers acted like a wick, which caused the moisture to more quickly absorb upward toward the dryer top layer.

After 4 weeks
Vermiculite: The top 1/8 inch (3.175 mm) was very slightly dry.
Coconut Coir: The top 2.5 inches was dry.
Sphagnum Peat Moss: The top 2.25 inches was dry.

As you can see, when it comes to providing aeration (allowing for more oxygen) without a danger to PH balance, perlite blows the competition away. When it comes to retaining moisture without a danger to PH balance, vermiculite is the undisputed champion.

What we learn is that if you need your soil to be more loose, provide better oxygen penetration, decreased water retention (to avoid root rot), and allow the plant roots to penetrate more easily and grow unrestricted, perlite is going to be the additive you're looking for. If you're looking for something to hold moisture longer, then vermiculite is your go-to friend.

Continued in PART 2

PART 2

With the issue of aeration vs water retention & PH settled, growers MUST understand that there are two other concerns regarding usage of these four additives. The first is in regard to nutrient retention, it's ugly relative "nutrient burn", as well as flushing your plants pre-harvest (or as regular maintenance against nutrient and salt buildup). The second is properly preparing your additives before using.

Because perlite does a very bad job of retaining moisture, it poses virtually no risk of dangerous nutrient buildup. Vermiculite, coir and moss all carry a significant risk of accidentally holding too many nutrients and/or salts. Vermiculite being the worst offender. Because water and the nutrients it carries soak into vermiculite's deep layers, flushing it clean can be difficult, requiring massive amounts of clean, PH neutral water. An absolute minimum of 5-6 gallons of water per 1 gallon of growing medium, depending on how much vermiculite is being used.

While coconut coir and peat moss aren't quite as bad as vermiculite, both act as like a sponge, which in-and-of-itself also requires greater and more frequent flushing of nutrient and salt buildup.

There is a flip-side to all of this. If you are a skilled and experienced grower with constant control over your growing medium, then you could actually use the nutrient retention of those additives to your advantage. Depending on how much you mix into your grow medium, you could apply your nutrients less often. This technique is like driving a car. No amount of reading will compare to your own personal experience. This is why novice growers should be very careful when using vermiculite, coir or moss in their medium. Depending on how many months your plant is growing from sprout to harvest, you may need to flush buildup from the medium with clean water once every month or two.


Why and how to prepare each additive for garden usage?

The manufacturing process of Perlite and Vermiculite are such that it is common for very fine, unwanted dust particles to arrive with your bags. Before using, you'll want to very fully flush any dust or foreign particles with clean water. An inexpensively great way to do this is with a 5 gallon paint strainer in a 5 gallon bucket. Buckets are pretty easy to find at various stores. The paint strainers are generally only going to be found in paint supply stores or online. Good news, paint strainers cost very little and can be reused many, many times before tearing (unless you're overly aggressive with the bag).


1) Place the paint strainer into the bucket while stretching the top band around the top edge of the bucket.

2) Pour your perlite or vermiculite into the bag/bucket.

3) Fill bucket with clean water.

4) Carefully collect the top of the bag together in one hand and lift from the bucket.

5) Dump the water out of the bucket.

6) Rinse & Repeat until water from bag runs clear.

Also, you could simply hold the bag of material under running water while gently moving the material around with one hand (sort of like massaging the outside of the bag) and get the job done faster.


Coconut Coir is most often harvested at oceanic coastal regions where coconut trees grow. This is why some growers have complained about their coir being dangerously salty. You must rinse this salt out or suffer a slow, stunted, if not dead crop of plants. Also, most coir comes in very hard blocks, which need to be broken up for proper preparation. Some coir brands may come with bits of gravel or stones. This is a result of lazy drying and preparation methods on the part of the manufacturer.

1) Use a screwdriver or similar object to break the coir block into small bits. You need to get every fiber of coir soaked and rinsed. Even small, hard chunks can be very slow to absorb water.

2) Place the paint strainer into the 5 gallon bucket while stretching the top band around the top edge of the bucket.

3) Fill the bucket about 1/3 deep with loose coir and then add water until the contents of the bucket are about 2/3 deep.

4) Using a mixing tool of your choice (I use my hand), mix the coir around until it is entirely soaked. This may require adding more water.

5) Once fully saturated. Follow steps 3 - 6 from the perlite and vermiculite process. The difference is that you cannot actually see the salt. So you'll need to use your judgment here to ensure the coir is properly rinsed.

Personally, when I purchase coir I actually break off a small bit and taste it for salt. It's not nearly as yummy as it sounds. If it tastes salty at all, I spend a lot of time soaking and rinsing it thoroughly.

Sphagnum Peat Moss is naturally acidic. Not only should you rinse peat moss to remove fine, unwanted particles, but if you can rinse it in a mild PH Up solution, it can help prevent acidic harm to your plants. Generally, I rinse my peat moss exactly like my coconut coir, with one difference. My final rinse of peat moss is the one in which I add a PH Up solution and let the peat moss soak in that solution for several days. Each day I use a PH tester (meter or strips) to test the water. When the moss & water is PH neutral for several consecutive days, then I drain the material for garden usage.


Continued in PART 3

PART 3

The last thing we need to cover is the prevention of damage to the plumbing of your home. Absolutely NEVER rinse any growing medium down the drains inside of your home. You need to understand that every sink, toilet, shower stall requires its own P-Trap. Also, there is at least one larger P-Trap in your home before waste water exits outside. The purpose of a P-Trap is to hold water in order to prevent methane and other dangerous gases from flowing backward through the sewer system and venting into the air of your home. Without those P-Traps your home is an extremely dangerous death trap for humans, pets, plants, pretty much anything that lives. If your home smells like sewer gas, you'd better check those P-Traps or risk severe sickness and death.



Perlite dust particles can sometimes float. Too many floating particles in your P-Trap will cause your plumbing to backup into your house. Trust me, you don't want sewage water flowing out of your drains onto your floors.

When rinsing Vermiculite, you may notice super-fine black sand. This is a normal part of the dust from the manufacturing process. Unfortunately, that sand is very dense (heavy) and does not flush through your plumbing.. at all. Not even under pressurized water. And once that sand gets into your P-Traps, it's never coming out. It will continue to collect until your P-Traps are too blocked work properly. Once that happens there is only one solution, you have to physically access the P-Traps to clean or replace them. If you live on a slab of concrete and your toilet, bathtub/shower P-Traps are literally under the slab, you are looking at a very expensive and destructive job. Hiring a professional plumber to do that work typically starts at a $1,000 and goes higher real fast. You could be looking at over $5,000 real easy. The black sand is too small & heavy to clean with a drain snake (manual or powered).

Coconut Coir and Peat Moss are not easily biodegradable. I shouldn't have to tell you what happens when you flush non-degradable fibers down your drains. Long story short, you end up with a sewer clog equal in difficulty to a large mass of tree roots growing into your sewer lines. Fair warning, products like Draino and other bio-dissolving chemicals have little to no effect on coir or moss fibers.


As a grower, what do you use and how much?

Generally I prefer growing in purely organic soil mix. I'll use Happy Frog soil from FoxFarm Soil & Fertilizer Company. For each 2 Cubic Feet bag of soil I'll include the following additives.

About 2-3 gallons of soaked coco coir. I only do this because I can increase the total volume of soil by a lot less cost-per-cubic foot. Coir is a lot less expensive than a second bag of Happy Frog. If you've got the money to spend, skip the coir entirely.

Per bag of Happy Frog I'll add two 8-quart bags of perlite. This provides great aeration and beautifully loose soil, not only for drainage & flushing, but also for fast root penetration and decreased likelihood of accidentally over-watering. Soil properly mixed with perlite can actually be difficult to over-water. It simply drains too efficiently. If I'm using coir, I'll include an extra 8-quart bag of perlite per 2 gallons of wet coir. Using this method, I can make a single bag of Happy Frog fill a lot more pots. I live in an area which costs me upwards of $45 to $50 per bag of Happy Frog.

I don't use Sphagnum Peat Moss at all anymore. There simply is no benefit to using an additive that I know is going to threaten the PH balance, which healthy plants require.

Mixing the soil itself is only half of the process. I use a top mulch mix to prevent the top of the soil from drying out faster than the rest. This is especially problematic when using a fan in the grow room. When the top of the dirt dries too fast, it leads to increased watering to prevent upper root damage. Increased watering in turn can lead to lower root rot from over watering.

For a top mulch I prefer inert material to help prevent molds or pests from penetrating into the organic soil itself. So, after my seedlings are nice and sprouted, I'll add a layer of mulch about 1/2 - 1 inch deep. My mulch consists of 50% Vermiculite and 50% Coir. This ensures that my plant's roots stay evenly watered top to bottom.

I don't grow in soilless mix. However, If I were to start, I'd go with about a 50% mix of perlite and coco coir. Vermiculite and peat moss are not required at all.


For Coconut Coir, I've used OrganicDews Expand Plus Coco Coir Pith, 11 Lbs block. Product of India. This coir came with no salty residue and no bits of stones or gravel.

For Perlite, I use medium sized pieces. I've used Miracle-Gro perlite (8-quart bag). The added nitrogen coating to the perlite is something I'd rather not have. However, it is an extremely small amount. Also, by fully rinsing the perlite clean, most of that coating gets washed off before it's used. I've had bad luck with Black Gold perlite from Sun Gro Horticulture (8-quart bag). Foreign bits of wood in the perlite are always bad things.

For Vermiculite, I prefer small to medium sized bits. Large vermiculite is good if you're growing outdoors and need major water retention in the soil.


Good luck, fellow gardeners!

A Word Of Caution on Perlite:
Perlite is a naturally occurring volcanic glass consisting of fused sodium-potassium-aluminum silicate. Tests conducted on Perlite have not identified crystalline silica as being present above the detection limit (0.05%). Although there are not published reports of adverse health effects from exposure to perlite dust, perlite contains crystalline silica (CS), which is classified as a hazard by inhalation. Long term inhalation of respirable crystalline silica dusts over a prolonged period may cause a non-cancerous lung disease (silicosis). Inhalation of respirable crystalline silica has been classified as carcinogenic (Group1) by IARC, a unit of the World Health Organization. Respirable crystalline silica is listed as a known human carcinogen.

Translation:
Since perlite (or any additive) should always be rinsed before use, and since you should never wash or flush additives down the drains of your home, proper handling of perlite represents an insignificant risk to your health. You pretty much have to inhale large quantities of crystalline silica over a very long period of time (10+ years) before there is a risk to health. This is why perlite is sold in stores everywhere, and is not a strictly regulated material.

Great post. I use a 5 gallon fabic pot to rinse and mix medium in. It drains well with no escapage.

?????

Oh boy.....

Looks like I'll be adding a bit more perlite to my brewing batch of supersoil. Another 5L bag should do it.

Cheers for writing this post. It's good to know the properties of these things. Especially if you've never used them before.

You want a formula for basic water only organic soil?

Start here and leave the Coco on the store shelf.

https://forum.grasscity.com/threads/easy-organic-soil-mix-for-beginners.1116550/

I add well composted Steer or Cow manure for the wonderfully broad bio's (myco) spectrum (over just the ewc).

1/3 peat
1/3 ewc
1/3 perlite
1-2 gallons of compost - steer/cow

This is a basic starting formula.

You need to add the buffer
The mineral
And the nutrient.

The amount of nutrient added - defines the time that nutrient is available to the plant....

Dr. Who said:

You want a formula for basic water only organic soil?

Start here and leave the Coco on the store shelf.

https://forum.grasscity.com/threads/easy-organic-soil-mix-for-beginners.1116550/

I add well composted Steer or Cow manure for the wonderfully broad bio's (myco) spectrum (over just the ewc).

1/3 peat
1/3 ewc
1/3 perlite
1-2 gallons of compost - steer/cow

This is a basic starting formula.

You need to add the buffer
The mineral
And the nutrient.

The amount of nutrient added - defines the time that nutrient is available to the plant....

Click to expand...

Cheers for the link. I'm still learning about all this. Definitely want to stick with organics if I can.

I've been doing a fair bit of reading on here. But it's a little hard to find some of the stuff mentioned but the peeps here.

Things like FFOF and a few other branded additives/mediums. This part of Oz we don't have those.

If you want a stronger mix for mature plants and start with FFOF, you're almost done. All you need to add is mild composted fertilizer like eco scraps (5-5-5), a little more aeration, a scoop of oyster shell (or dolomite) and yer done! No "cooking" required.
If repotted shortly before flipping to 12/12, this mix will keep plants happy until mid flower. Then they can be finished with nutrient teas.

To reduce dust dont open the bag up first thing. Use a hose outside. Make two holes in the bag. One at the top and one at the bottom. Stick the hose in, turn it on and let the water run out the bottom. Once it is all wet you can open it up.

Thank you so much for this great comparison! I have a new one of kind soil supplement/amendment that is optimal for water retention and also for aeration, in addition it feeds the soil organic silica and micro and macro nutrients. These are immediately bioavailable to the plant which makes the stalks and leaves really strong and healthy. This is all natural, certified for organic growing and at my grow it saves us 40% water - we also get about 30% more yields and our crop is super healthy and strong. 50% more root growth and the stalks of the plants are about 25% thicker than the plants we have grown without Harvest Gold Silica. Have you heard of it? Hit me up if you'd like to know more. It's recycled from 120 year old gold mine tailings, so it doesn't have to be mined & we hydro wash it so it is free of debris. It does not float like perlite does, it stays in the soil for your full grow cycle and continues to feed the soil with silica and other nutrients and it bonds to anything else you are feeding it and drives nutrients into the roots and enriches the soil, no more nutrients or silica running straight through, it stays in and slowly drains at just the optimal rate to prevent root rot. We use fox farms also and getting bad ass results. It improves the performance of coco because of the unique granular shape - perfect aeration!

Great contribution to a better understanding of these soil enhancers.