Adventures With Gritty Mix

If you found a blog this obscure, you were probably looking up gritty mix. It's supposed to be excellent for plants although in the beginning it was unclear to me why. The explanation was sixty thousand kilometers long so that took care of that idea for a few months. It fell under the category of "I'll read that someday."

But the gritty mix is all over the web you just have to find out wtf is up with this thing anyway. You find out that the mix involves an odd assortment of ingredients in it, including the some strange substance normally used for baseball diamonds. WTF is up with that, right.  I thought baseball players were born with and walked around in their own personal cloud of dust and that's how you knew you'd grow up to be a baseball player. O well. 

The thing is that people who use this gritty mix swear up, down and sideways that the stuff was uber. I was particularly interested in its ability to keep plants from drowning. I never had the patience for figuring out which plant needs how much water and when. As a result, my jungle rotates between near-drowning and being bone dry, eventually leading to inevitable death by black thumb. 

This is annoying since I don't keep plants for the love of watering them. Watering is just something one needs to do so plants don't die. If this gritty mix will take guesswork out of that process, even the quest for baseball stuff might actually pay off.

It turns out it does!

Before You Begin


This substrate is not a miracle cure for what ails your plant. You will find, after experimenting with it, that it might not suit the way you conduct your container gardening. This post will give you the basics of it and you will want to tweak it but it is strongly suggested you try the original formula first so you have a baseline. It's effectiveness will depend entirely on your climate, watering and fertilizing habits. 

Two things to remember: The first is that plants in the ground and plants in a container are, for all practical purposes, two different creatures. What we want is for the plant growing in the container to not notice it isn't growing in the ground.

Second, container soil is not really about the soil, it's about water. When you water a plant in a container, that water goes down (gravity, wouldn't you know) and some of it exits through the drainage hole at the bottom. But it turns out that depending on your potting material, water will either drain freely or most of it will sit at the bottom of your pot, eventually drowning your plant.

How plant roots manage water in the soil is an interesting story having to do with things like capillary action, osmosis, pressure, hydrophilic molecules, surface tension and even gravity. These are the same processes in action when you use a tissue paper to absorb a bead of water on the table. When these processes are overloaded, you end up with the same dripping, disintegrating mess.

When the particulates in the soil are very small or when the soil contains absorbent materials (like peat), the water that is not immediately absorbed by the plant roots will gradually make its way down to the bottom of the pot and stay there. This is called perched water. If the roots of your plant is above this perched water, it will probably be fine. But that is not how plant roots behave--plants colonize their container and often, their roots will go all the way down to the bottom but the water just sitting there will eventually disintegrate them. As a result, you lose root mass and you risk both bacterial and fungal melt climbing up to the rest of your plant's roots. So what you want is a kind of potting medium that holds just enough moisture to support the plant but not so much that most of it will just be sitting there at the bottom, being generally obnoxious.

Fortunately, there is science behind this conquest of the water in the pot. There is no need for magic thumbs of any color, garden woowoo or any such nonsense. 

Pros and Cons 

Pros: 

• It is nearly impossible to overwater a plant in gritty mix or even its 5:1:1 version. Because it has no tiny particles to trap water in the crevices, what water that stays in the pot is only what the individual components can hold.
• Since this is a soil-less mix, you have absolute control of the nutrients that your plants will get. 
• This is the perfect substrate for most succulents and potted trees. Growing mesembs in this mix proved to be too tricky to bother with though. Too annoying for tropicals however, even in the 5:1:1 mix.
• It is very easy to flush to get rid of unwanted build-up in the substrate so that it is no longer necessary to repot a plant every year the way it would be if you are using soil. Eventually, the organic component will break down (the bark) but this takes anywhere from 3 to five years. 
• Roots grow faster in this mix, ultimately giving you stronger and more vigorous plants.
• This substrate will allow you to follow the "fertilize weakly weekly" regimen

 Cons

• Components are a pain to find and put together. There are now online entrepreneurs who sell this mix but you will save tons if you make it yourself.
• Transplant shock is the first problem you will encounter, usually because your plants have been spending a lot of time trying not to drown in perpetually waterlogged soil. When moved to such an airy mix, they will wilt from lack of water. Learning how to water plants in gritty mix can be tricky. Adult adeniums, for instance, will have to be watered more often than you are used to when you transplant them--nearly every two days in the summer until the plant settles in. In any case, adeniums should be in 5:1:1 mix, not gritty mix.
• As you will see, much of the water you will pour in will flow right out. This is a good thing for the plant but not so good since you want to conserve water, not waste it. The workaround is to put your pots in locations where plants in the ground will benefit from the runoff. It's more work but you'll feel good about not being a dick about wasting water.
• Having full control of the nutrients your plants get means you have to pay attention to what you feed them with. Plants do not just need nitrogen, phosphate and potassium. They need other elements usually found in the soil but absent in a soil-free substrate. Fortunately, you can buy fertilizers with these elements added in the proper proportions. 

Building the Mix

The gritty mix was developed by a master gardener known in the forums as Al Tapla who freely shared the soil mix recipe that he has developed over years of experimentation. I am just repeating the information here, with some notes of my own.

Ingredients: 

1. tree bark fines: fig, pine or hemlock; make sure it is uncomposted.The easiest way to get this is at a pet store where they sell bark for reptile habitats. I found this is worth the price since they rarely have to be sifted and the fines are more or less the same size 
2. fired clay (crushed) like Turface, Napa Floor Dry or Akadama (very expensive). If you can not find this, you can use crushed pumice. 
3. Crushed granite also known as poultry grit, the kind chicken farmers use for their chicken feed. There are different sizes of poultry grit. What you want is the size used for adult chickens. This is the ideal size but I have used the normal pea-sized gravel sold in garden centers and it worked fine. Remember you want granite. Chicken grit is made of different materials like oyster shells and granite is what you want because it is inert and will not affect the chemistry of your substrate.

There are two versions of this mix, depending on the proportions of the ingredients. One is known as the 5-1-1 which is composed of five parts tree bark and one part each of gravel and fired clay. The other one is the gritty mix or the 1-1-1, composed of one part each of the three ingredients.

The key to this mix, as you will soon realize, is not so much the ingredients as the size of the particulates in each. You need to get the size of the particulates as uniform as possible and they have to be no smaller than 1/8 inch and no bigger than 1/2 inch.  This will ensure that there will be enough air pockets in your medium to provide aeration that will allow plant roots to do their business.

Al Tapla suggests uncomposted bark fines from fig, pine and hemlock trees, mostly because their chemistry ensures that the bark will not disintegrate too fast and clog up the soil. The bark component will provide the highest absorption of water and will hold that water longer than the other two ingredients.The thirstier your potted plant is, the more bark it will need.  It's an irritating chore but sifting is important. You want the dusty bits out or they will just fill up the nooks and crannies that should have been air pockets.

Fig bark, sold as orchid bark. The powdery bits shown here must be sifted out before use.  
You can also get bark fines from pet stores, in the reptile section. 
They usually have very little dust, eliminating the need for obsessive sifting.

Fired clay or calcined clay is an inorganic material that is mined, fired and then crushed to the desired particle size. Until recently, it was most commonly used as soil conditioner for athletic fields. It looks like this:

Out of the bag, fired clay is more or less uniform in size 
but it has powdery bits that must be sifted out.

Finally, gravel. You can use pea gravel--you can get this at any big-box store. You can also use crushed gravel which, apparently, comes in different grit sizes. You need something called grower size grit. I have never seen it and already had a bag of gravel from previous projects so I used that.

I know there are really big bits, If I am potting up a tiny plant, 
I sift them out. Otherwise, I don't bother. Powdery bits, though, are washed out.

Now. I did not like sifting these things. So now, I wash the crushed granite, it's faster. I hammer the tree bark a bit, to crush the big pieces. Then I dry-sift that using just regular insect screen. The fired clay, I definitely will not bother with again. After dry-sifting a bucket of it, I'll be damned if I will put up with that shit again. So, I now use crushed pumice instead of crushed fired clay--it is also inorganic, porous and holds roughly as much moisture as the fired clay. 

Crushed pumice. Note that the size range is pot-ready and 
usually does not contain powdery bits.

Of all these components, fired clay is the hardest to find, I realized. The most painless way to get it is from Amazon where I also get pumice. The first tree bark fines I found was crushed fig bark intended for orchids. This material is ridiculously expensive and the pieces are way too big. So go to a pet supply store, head out to the reptile section and pick up a bag of bark fines.They're usually pine bark.

When you have everything, just mix them together. It will look something like this:

That's it, you are done.

Tweaking the Mix

Think of the gritty mix as a starting point. In its 1:1:1 form. you can use it for plants that need moisture but absolutely hate standing water. For instance, I use it for agaves, adeniums, my one pot of hoya, my various pots of semperviven, dorstenia and even some of my gasteria. But I will not use it for my one pot of lithops which is potted in pure pumice. My haworthias are also in pure pumice but they were potted before this adventure and I didn't want to bother moving them into gritty mix. 

I have some aeoniums and for them, I added more bark so that the mix is more like 4 parts bark to one part each of the other two components. For plants like coleus, I mixed one part gritty mix with one part potting oil. It drains fast but not so much that the thing goes limp after two days. I would never use it for elephant ears, for instance; they like to be in swamps after all. 

The brilliant thing about the gritty mix is how perfect it is for plants you are instructed to "keep moist but do not over-water", as if that made sense.  I have been using about half an inch of calcined clay as top-dressing and this also serves as a moisture indicator for me. When it is completely dry, I water.

Possible Substitutes
In places where tree barks might be difficult to find, crushed coconut shells are good alternatives as long as the dusty bits are sifted out. Coconut coir chips are also available but again, make sure the small particulates are sifted out. Instead of crushed fired clay, use crushed pumice. You can probably use perlite as well but they are usually so crushed they're almost all powder. Perlite also tends to float to the top when you water which is irritating. Vermiculite is worse. These last two materials help prevent the soil in the pot from getting compacted but they're practically useless for speeding up drainage or, indeed, lowering the perched water table (PWT) in the pot. 

Do not use sand (particles are too small) if you want to keep the PWT down or eliminate it altogether. I don't use peat either---sphagnum has nasties that I don't really want to have to worry about. 

Random notes on ingredients and other uses:

• Can I use clay pellets? No. It breaks down so fast you'll quickly lose the aeration ability of the mix
• Can I add peat to the gritty mix? Sure. but it wont be gritty mix anymore for the same reason stated above
• Can I use gritty mix or 5:1:1 for tropical plants? Sure. Al Tapla reports that he does. But I haven't succeeded using either formulation for plants as thirsty as, say, Dama de Noche or coleus. This failure, I am sure, was because I had no patience to babysit them during the transition which turned out to require watering once or even twice a day until they adjusted
• Can I use gritty mix or 5:1:1 for swamp plants like alocasia? What the hell. Why even think of using a fast-draining mix for plants that need to be in swamps? Hello?
• Can I use it for mesembs? Lots of debates and long answers. My bottom line is no. Mesembs are special kinds of monsters.

Updated April 8 2015

Related Post: Adult Adenium In Gritty Mix

Next: Things to know when moving plants from regular soil to gritty mix

Further Reading:

Al Tapla's basic recipe has gradually changed over the years. Here is an early version of this mix but this link is my favorite and it is a must-read. It has a comprehensive discussion of water movement in container soil.