Hey guys! I haven’t exactly been chatty here on the forum.. despite logging in almost every day
but I have made some great friends and prospered from some amazing trades. I’ve really been wanting to contribute but feel a bit of a novice and have been looking for how I can help. So here is my first offering!
I have been researching and playing around with different soil mediums for a few years now. I don’t particularly like store bought mixes feeling they are lacking essential components. But traditionally my mixes have always kind of been on the fly and by feel. Basically what looked good to me and had the ingredients that I thought were important. However, there was a very important concept that I was oblivious too and now believe was to the greater detriment of everything I have ever grown, even what I believe I have succesfully grown. It is called the Perched Water Table (pwt).
This exists naturally (known as ground or surface water) but also exists in containers/pots and I think is important to understand. The easiest way to understand how it works is to think of soil as a sponge. Literally. You can also see it in action very clearly with an actual sponge. If you take one of those thick sponges that you use to wash your car with, set it on a table, and water it until water spills out, it will still retain much of that water. If you look more closely, you will notice that a bottom portion of the sponge is visibly holding more water than the majority of the upper portion. It simply won’t drain completely, leaving the sponge wetter at the bottom than the top. Although the top is moist, the bottom will be soggy. The same thing happens with soil in a container.. almost always.
Without getting too technical, the reason for this is due to a mediums ability to wick vs the force of gravity. At some point, the two forces reach equilibrium and that point is the perched water table. In typical store bought soils, it can be as much as 3 inches or more.
Why is this important? Because it dramatically impacts root health. In fact, there is strong evidence to support that root health in container grown plants is the primary limiting factor for a plant reaching its full potential. Roots need oxygen to grow. When a perched water table exists, it is no different than a puddle of water. So, even if you wait to water until the pwt totally dries out before watering, the roots at that zone will be locked into a cycle of decay and regeneration. As the roots sit in water, they suffocate and start to die. As the pwt dries out, the roots start to regenerate. This is very stressful for the plant and consequently, the plant is using a lot of its resources to accommodate this detrimental everlasting cycle, instead of maximizing growth and health.
Worse yet, this may be the most common reason for the eventual decline/failure of plants maintained in pots by so many people. I know, even as diligent with watering as I like to think I am, how many plants I have lost to rotten roots.
So.. there has been a new approach around for a few years and a huge following that says it has dramatically improved their growing experience. It is commonly referred to as The Gritty mix (or 1-1-1 mix because of the ratio of ingredients). There are volumes of information about it on another forum. I don’t know of the policy on STS about linking to other forums, so I won’t do it. Plus, I want to include this here locally as a resource for our own amazing forum. But if you are interested, PM me and I can point you in the right direction. The truth is that there is too much info for me to totally consolidate and probably much better informed experts on the matter than myself.
But please, let’s try to address as many details here on this thread so other users on this forum can profit.. without having to do all the research I have done! I will try to answer as many questions as I can. If you want more info, I’ll be happy to share.
So before we get into how to make the mix, let me preface with a few points. First, if you are committed to growing organically, this may not be for you. It may be.. but it requires soluble nutrients and I don’t know what the availability of soluble organic fertilizers is. Typically, organic nutrients exist as components of a medium (i.e. compost). Personally, I tend to be in the camp that a chemical is a chemical, whether produced by nature or by man. Actually, I don’t think things produced by humans are any more unnatural than a bee producing honey… but that’s a whole other discussion. From a plants perspective, Nitrogen is Nitrogen. It doesn’t care how it was made. It uses it just the same. Now.. using chemical pesticides is another thing and something I definitely try to avoid.
Second, although there are only three ingredients necessary.. they can be difficult to source depending on where you are located. There are alternatives I can suggest or you may have to get creative. It is also a bit more laborious but typically can be much cheaper than buying ready made mixes.
Thirdly, it may require a change in habit or approach to watering. The short of it is that you may have to water more frequently than you are accustomed to.. like every two to three days. Because of the nature of most of us on here, I don’t think that will be a problem. But if you travel or simply don’t want that much maintenance, it should be considered. Remember, this is about maximizing a plants potential!
So the point of the Gritty Mix, is to get rid of the perched water table and allow the soil medium to be fully aerated at all times, while maintaining constant water and nutrient availability. The pwt is eliminated by keeping medium partical size greater than 1/16-1/8”, hence the term gritty. This reduces the mediums ability to wick against gravity and provides plenty of space for aeration. It also will not compact over time and easily rinses away from roots when repotting.
The Gritty MixSo the mix is simple. It consist of equal parts:
•Turface
•Crushed granite
•Pine bark fines (small sized mulch.. shredded or partially composted, not large nuggets)
•May need to amend with small quantity of dolomitic lime or gypsum if your preferred soluble fertilizer does not contain calcium and/or magnesium.
If anyone really wants to pursue this, I’m sure there will be many questions about these components. I will wait to address them more fully as they come up but here is a brief explanation of each and where you might source it in the meantime.
TurfaceThis is a soil amendment used on sports fields to help drainage. It is calcined (fire expanded) clay. It has a tremendous amount of surface area via interior porosity. One pound of turface has a surface area equivalent to 14 acres! This is what primarily holds water and nutrients. Can be sourced in the US from John Deere.. called AllSport.
Crushed graniteMostly for aeration and reduction of wicking ability. Also holds small amount of water on its surface. Can be sourced from feed stores as a poultry grit product. You have to be careful that is “grower” size.. for full size chickens, and not for chicks.
Pine Bark FinesMostly used as a filler because it is much cheaper. Also provides an organic component and offers water and nutrient retention. Sold as mulch or soil conditioner. Can also use reptile or orchid bark in a pinch, although may be pricey after sifting.
Making the mix:
So, the laborious part is that you have to sift these components to get the right size. You need two screens. One to sift out the particles that are too large and one to sift out the particles that are too fine. I made mine with wooden frames, one with ¼” hardware cloth and the other with insect screening. The important thing is that you can sift out particles that are less than ~1/8” and greater than ¼”.
The pine bark fines need to be sifted for too big and too fine. The turface has to be sifted for too fine. And the granite may not need to be sifted at all.
After sifting, you just mix the three ingredients in equal parts, 1-1-1.
WateringNow, about watering. The great thing about this mix is that you can’t really overwater, because there will be no perched water table. In fact, you don’t want to water in sips and want to always water thoroughly whenever you do. You want to water slowly and until about 10-15% of the total volume of the water washes out the bottom of the pot. This has the added benefit of flushing any salts that may have built up in the mix. Also, because the medium has no nutrients, you will have to add a soluble fertilizer (complete with micronutrients). I think the easiest approach is to water with fertilizer every time, at one quarter strength (a tsp per gallon for most fertilizers). Alternatively, you can water with fertilizer at full strength once a week and use plain water in between.
So, that’s about it.. lol. Sorry, I know that was a long post but it’s a rich topic with a lot of aspects. I do believe it is sound science and that the benefits are many. I have actually been using a different mix, from the same creator of this one and based on the same principal, with great success for the last couple of years now. It is mostly for short season (veggies and such) or for short term plantings. This gritty mix is ideally suited for cacti and succulents or container plants that won’t be repotted for two or three seasons. I am currently repotting, and starting some new (difficult to germ seeds) in this gritty mix for the first time, so I can’t personally vouch for it yet but have a high confidence in its performance. I will share my results as they become evident. There is literally a legion of people who swear by this mix.
Despite just beginning to use this mix, I feel I have a thorough understanding of the how, what and why. So please, ask away and I will clarify what I can. Better yet, maybe some other members can start their own trials and we can see where it leads. I really think this will be, maybe, the best medium one could ever want for growing cactus and succulents, and really for any terrestrial plant. And if anyone is interested in the other mix, let me know and I will share that too. It’s all I use anymore and is much cheaper and better than store bought. And it’s less maintenance too.. normal watering but it will have a bit of a pwt, just a more acceptable one.
Author
Topic: Maximizing Plant Potential - a superior potting mix (Read 8254 times)