How much gypsum in gritty mix

demeter_26December 2, 2010

Hi everyone,

I am about to plant a (3 gallon) Fairchild mango tree in a 25 gallon container using Al's gritty mix as the medium. I have the Turface, Granite grit, Pine bark and the Gypsum ready to be mixed. Could someone please tell me exactly how much gypsum to add to 25 gallons of gritty mix? This is my first time trying the gritty mix and I want be very exact on this part since I know that too much gypsum could burn the roots and too little would not lower the pH enough.

One other question: If I don't use the 9-3-6 foliage pro liquid fertilizer, is there another good liquid fertilizer that someone would recommend using in this mix that contains all the minors as well? And could a control release fertilizer(CRF)be used with Al's gritty mix?

After reading so many links and threads on this subject,

I would like to thank everyone, especially Al, for helping me up to this point in this project.


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tapla (mid-MI z5b-6a)

1.5 cups


    Bookmark   December 2, 2010 at 10:14AM
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Thank you Al.
Home Depot sells a product called "soil acidifier."
It says on the package that it's "derived from sulfur and gypsum." Al, does that seem to be within the parameters of what we are looking for or should we search for something else that just says gypsum on the label?
Jon and Christine

    Bookmark   December 2, 2010 at 1:48PM
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tapla (mid-MI z5b-6a)

Gypsum (MgSO4) neither raises nor lowers pH so that you'd notice. When I feel a need to lower pH, it's usually the soil solution I look to, and I do that by using white vinegar in the irrigation water.


    Bookmark   December 2, 2010 at 1:55PM
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Hi Al,
Thank you for your quick response about gypsum and pH.
I think, though, I made a very serious mistake.
We mixed the 1.5 cups of the "soil acidifier" by Espoma into the 25 gallons of gritty mix thinking it was Calcium sulfate(gypsum) and then Chris and I got suspicious when the mixed burned our hands while mixiing it in. Come to find out the "soil acidifier" IS NOT gypsum it is only "derived" from gypsum. It is pure sulfur but not calcium sulfate. Now we are caught in a real dilemma.
The soil acidifier is granular which could mean it is "control released." My question Al is first, are we correct in our suspicions based on our assumptions?
And, second, if so, can we fix the problem by rinsing out the sulfur adequately that is now in the mix by running a lot of water through it and then afterwards add the real gypsum to the mix?
The garden center informed us that Gypsum is Calcium sulfate. Is there Magnesium sulfate Gypsum as well?
Sorry for having created an unnecessary situation.
Your input would be greatly needed and appreciated!!
Thank you Al.
Jon and Christine

    Bookmark   December 3, 2010 at 6:51AM
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Al, while we are at it, may I ask a "stupid" question: what can gypsum do to plants, please?



    Bookmark   December 3, 2010 at 8:34AM
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tapla (mid-MI z5b-6a)

So sorry. I'm surprised that no one else caught the gaff. Epsom salts (MAGNESIUM sulfate) is MgSO4; gypsum is indeed CaSO4.

I really don't know what that amount of sulfur is going to do to a soilless medium. S is generally considered insoluble, but that much is bound to have SOME effect on the planting. It's not likely to rinse out. Sometimes, plants shed foliage in response to excess S, but if you have to have an excess of any nutrient, S is probably the least noxious.

I know you said it was granular, but might it be described as 'pelletized', or is it in powdered form? If powdered, you might try a thorough screening, rinsing as you go. If it was pelletized, and the pellets are smaller than your soil particles, the right size screen might enable you to screen most of it out. The larger the S particles the less the issue will be.


Xuan - gypsum serves (primarily) as a source of Ca and (secondarily) S(ulfur) without changing pH of the soil or soil solution. As a Ca source, gypsum is more soluble than dolomitic (garden lime) so gypsum in excess can contribute significantly to the EC/TDS (level of salts) in the soil and make absorption of Mg difficult.


    Bookmark   December 3, 2010 at 9:49AM
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Thank you, Al. (but it's still alot of "stuff" to me...huhuhu!)

Anyway, if I give some gypsum to my mix, in addition to slow-released fertilizer... I'm assured of adequate nutrients to the plants. Right? Wrong?


    Bookmark   December 3, 2010 at 10:41PM
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Thank you Al! Great idea! We will screen the mix and try to remove the majority of the sulfur. Will let you know how everything turns out.
Have you ever grown a mango tree in the mix?
If so, would you know if a mango tree likes a slightly wetter (more Turface) or drier variation (less Turface) of the 1:1:1 gritty mix?
Al, thank you for your patience and insight.
Jon and Christine

    Bookmark   December 4, 2010 at 8:10AM
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tapla (mid-MI z5b-6a)

I used to regularly 'push the zone' and grow all sorts of stuff that wanted warmer than I offered, just because it was unique to where I live, but I decided that I'd rather limit the extra effort it takes to maintain tropicals and subtropicals to plants that are appropriates for bonsai. I can't say I've grown a mango in the gritty mix, but I know people who have (right, Nance?), and I've grown SUCH a wide variety of trees in the gritty mix that I feel pretty safe in saying it's doubtful you'd ever find a mix on the shelf that will even come close to providing the growth/vitality potential the gritty mix will. I'm not saying that because it's a recipe I developed, I'm saying it because the recipe does a superb job of coming as close as possible to providing a mix of air/moisture that ensures good root health/function.

EVERY time I take one of my trees to a (bring your own tree) workshop conducted by a bonsai master, he/she almost always comments on the excellent health of the trees. Any who might be used to rubbing elbows with some of the world's foremost authorities on tending trees, in workshop settings, will know that for a master to comment on the health of the tree, it has to be something he/she is unused to seeing in workshop settings, which makes it a notable compliment.

Generally speaking, trees will do best in soils that need watering more frequently. IOW, if I had the choice between a soil that required that the plant be watered daily, and one that required watering every 3rd or 4th day, it's a near certainty that the soil that needs watering daily has the greater potential for growth and vitality. Your decision then, is deciding how often you want to water. It does no good if you try to squeeze the extra growth/vitality out of a planting by using a soil that requires frequent watering, only to discover you can't keep up with the plants' requirements, introducing the limiting factor of drought stress.

I think the gritty mix works best at the 1:1:1 ratio, but I understand that it may need to be adjusted (by adding more Turface and decreasing the amount of granite) so growers can keep up with watering needs, but here's the skinny on that: IF you are increasing the water retention to get the plant through 1 or two days between waterings, it won't impact growth/vitality so you could notice; but, if you're intentionally increasing water retention so you can go more than 3-4 days between waterings, you probably are giving up some growth/vitality potential for the convenience. This only applies to mature plantings where the entire soil mass is well-colonized by roots. In new plantings, say where a cutting is stuck in a 3 gallon container, it's possible that you would be using the 1:1:1 gritty mix with screened ingredients, and could go as long as a week or two between waterings with no ill effects. The key point is whether or not you are introducing a PWT to extend watering intervals.

BTW - I'm ALWAYS patient and happy to offer any insight I might have, to friendly people who want to improve their skills by increasing their understanding of the plant-related sciences. It's fun, and I look at it as a natural extension of the satisfaction I get from nurturing plants. Nurture plants or nurture people who grow plants ..... it doesn't seem to matter. I get equal gratification from either. ;o)


    Bookmark   December 4, 2010 at 11:19AM
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tapla (mid-MI z5b-6a)

Oops - I missed Xuan's question!

".... if I give some gypsum to my mix, in addition to slow-released fertilizer... I'm assured of adequate nutrients to the plants. Right? Wrong?"

Mmmmmmm - maybe a little of both. The following are parts of a reply I just posted a few minutes ago on the soil forum:

We cannot bake a plant grow or maintain vigor at something beyond its genetic limits by adding more of something that is not deficient or limiting. Anything soluble in the soil solution that is in excess is counterproductive.

As in the diet of animals there is an ideal balance of protein, carbs, nutrients, etc. The same is true of the balance of plant nutrients in soils. Both the concentration AND ratio of these nutrients to each other are an important consideration if we expect to be able to coax plants to grow at or near their genetic potential. From the department of redundancy department comes the fact that adding more of anything than is necessary to make it a non-limiting factor is counter-productive.


There are three basic questions we should take into account and be able to answer yes to, when we develop our nutritional supplementation. They are:

* Am I supplying all 13 of the essential nutrients plants normally get from the soil?
* Are the nutrients present in a ratio that is favorable to each other.
* Is the o/a level of dissolved solids (EC/TDS) in the soil in a favorable range.

If you cannot answer 'yes' to all these questions, your plants will only be able to grow within the limitations the imperfect conditions allow. Don't panic. ;o) There is no need to get technical to the nth degree. You can be pretty sure you're doing close to the best you can do if you familiarize yourself with the nutrients plants need, then read the labels to make sure your plants are getting them.

Using a 3:1:2 ratio fertilizer will go a long way toward ensuring that you are supplying the primary macro-nutrients in a favorable ratio. Using a fertilizer like FP 9-3-6 ALSO ensures you are supplying the secondary macros AND the micronutrients in a favorable ratio, that being in a ratio that approximates that in which the plant actually uses these elements.

The main nutrients to look out for are Ca and Mg. MOST soluble fertilizer lack these elements, which is why dolomitic lime is such a valuable commodity for those of us who make our own soils. When the increase in pH caused by the lime is a little more than soils like the gritty mix can tolerate, and when our fertilizer doesn't provide it (Ca), there is an advantage in using gypsum (CaSO4) as a Ca source because it doesn't raise pH. When you need to use gypsum as a Ca source, you usually also need to use Epsom salts MgSO4 as a Mg source. Here again we need to look to not only the availability issue, but also to the RATIO. Supplying only Ca (gypsum) can make Mg less available/difficult to absorb, so we need to be sure that the ratio of Ca:Mg is favorable.

When I first discovered FP 9-3-6 a few years ago, I got really excited for YOU guys. I was already taking appropriate steps to ensure all my plants nutritional needs were being met by doctoring my MG fertilizer. I was VERY pleased with the results of what I had done with the MG, and didn't notice any difference when I switched to the FP. It made me happy for 2 reasons. 1) I didn't have to mix all the other 'stuff' into my MG fertilizer; it really simplified things, and 2) I didn't have to teach you guys how to do it. ;o)

Don't be shy about asking questions if you don't understand, Xuan. I'm betting Demeter won't mind - especially since it's so on topic.


    Bookmark   December 4, 2010 at 11:54AM
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Hi Al,
You are correct in assuming that I would not mind :)
I am always amazed how you painstakingly cover every detail when you are explaining something. You never just glaze over an answer just to satisfy the inquirer. Initially I wanted to grow vegetables (mainly tomatoes) using the 5:1:1 mix and tried to avoid the urge of getting into what I thought was a very complicated and time(and o/a)-consuming hobby like Bonsai trees. But as I prepared the gritty mix for the mango tree, I could feel that distant urge creeping past the fear and into that bowl of passions I cherish. After reading so many of your writings in this forum, you do nurture people and get them past their horticultural fears and difficulties which enriches their experience which in turn bleeds over into other parts of their lives as well.
There are elements that unlock soil potentials, as you do, Al, with people's potentials. Anyone can see that you are both a true artist and scientist and it's pleasing for Christine and I to read your professional presentations on the subject.
BTW is there an actual name for the activity of

I suppose we screened out the majority of the sulfur.
As a safety measure, we added a HALF CUP of Dolomite lime (CaCO3 + MgCO3)(alkaline) to try to neutralize any residue of the Sulfur (acidic) that might be still remaining and ONE CUP of Gypsum to satisfy the originally needed Calcium supplement (of 1.5 cups of gypsum) for 25 gallons of gritty mix.
Time will tell if the total balance is right.
We'll keep in contact.
Thank you again, Al.
Jon and Christine

    Bookmark   December 5, 2010 at 8:32AM
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tapla (mid-MI z5b-6a)

Your comments mean a lot, Jon. I've received a lot of positive responses over the years, but yours is one of the nicest. Thank you very much.

I think that the most valuable information you can put forth on these forums is the information that can be offered in absolute form, and I try to speak as much as I can in absolutes. You can quickly get yourself into trouble though, and invite contrary opinions when your offerings ARE in absolute form ..... unless you know enough about the topic to qualify what you're saying as you go. These qualifiers are a way of isolating and dealing with the variables so you can say what you want to say w/o someone jumping in to correct or argue, which inevitably leaves people confused and wondering who/what to believe.

I just left a nice compliment for a poster on the soil forum yesterday. I said "Dan - When reading a post with as many absolutes as yours, I usually find a point or points that I might disagree with because they were offered in a context too broad to be taken as written, but I found your post excellent and exactly on target." I complimented him because he posted a long post with many absolutes in it, yet he offered them in such a way that any logical or fact-based argument would be almost impossible.

Most of the disagreements I have on the forums are with the same people over and over. Their arguments are usually very weak or even not even applicable to the main theme/topic. No matter how hard you try, you can't avoid disagreement from this quarter, because it isn't about informational issues, it's about personality clashes. Jealousy or bruised egos and the retaliation that accompany them are often a big problem, too. Anyway, sometimes I offer the extra information to help others learn, but as often, I offer it to give pause to those predisposed to argue the point. In the end though, I think that no matter which reason prompts the added info, SOMEONE will potentially benefit from it - at least that's my hope. ;o)

About the name for the "activity of
"bonsai-tree-growing" ...... I know that bonsaist is a word, but somehow it just doesn't feel or sound right coming off the tongue. I usually describe myself as a 'practitioner of bonsai' or a 'bonsai practitioner'. 'Practice' seems to fit because it's not an exact science and it's ever-evolving - like a doctor's 'practice'. It's amazing what you can learn by keeping up with new innovations. Would you believe there are techniques I've used to remove a branch from one side of a tree and move it to another? or that you can drill a hole in a tree trunk and thread a thin branch through the trunk so it comes out the other side, and the branch will grow there? or that you can graft roots onto the trunk to make the root spread more even/attractive? Much more ....

Good luck with the mix. I sure hope everything turns out to be ok. If you ever have questions about what you're doing (re soils) and want to run it past me before you act - always feel free. I'll surely help if I can.


    Bookmark   December 5, 2010 at 10:31AM
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We hope you're having a great weekend.
Have you ever heard of or had any experiences with AZOMITE trace mineral soil by OMRI? Since it has Selenium along with another 67 trace minerals (which nutritionists say, are desperately lacking in the soil and therefore in our fruits and vegetables), do you feel it might be a viable supplement to add a little to the 5:1:1 mix in which my tomatoes are growing? I am using the FP 9:3:6.
Would it be overkill? Perhaps there is, but we didn't note of any Selenium included in the FP 9:3:6 profile.

BTW since the mango tree we planted in the gritty mix is at Christine's home, she is using MG 12:4:8 liquid fertilizer on it which I believe is not as micronutrient complete as the FP. We've heard about using S.T.E.M. to supply trace minerals. Would it be a good supplement to add to the MG fertilizer for the mango tree? We wanted to see the specs on S.T.E.M. but we were only able to find a product called Peters STEM trace mineral mix. Would that be the one people are talking about in the Forum? Or is there another one (preferably a liquid) that you are more familiar with?
If so, what website or company could we buy it from or research it?
Thank you kindly,
Jon & Christine

    Bookmark   December 5, 2010 at 12:45PM
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Looks like this thread is slightly outdated, but hoping to get an answer. Al, I've read a lot of the information you've put on here and I am going to try my hand at the gritty mix. I have mainly succulents (jades/aloe) and a few christmas cacti. I've located all of the ingredients I need but my question is:

for the gritty mix, do I need to use gypsum if I am using Foliage Pro (9:6:3)? I read up on FP and found that it does have Ca and Mg, but am wondering if the amounts are high enough to avoid adding the extra gypsum.

Thank you for putting so much time into this forum, I have been reading it for quite awhile and have learned so much!

    Bookmark   February 9, 2013 at 3:42PM
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Loveplants2 8b Virginia Beach, Virginia

Hi rlk237,

I just wanted to chime in and give you a quick reply.

Hopefully Al will be here to help you, but i will say that if you are using the Foliage Pro 9-3-6 with your plants in the Gritty Mix, it isn't necessary to add the Gypsum.

They will be receiving all the essential minerals and nutrients with the FP.

Good choice by the way!!

Hope this helps..


    Bookmark   February 9, 2013 at 5:32PM
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