Granite grit sounds like very small pea gravel. This might help drainage some especially in containers, but would not add nutrients.

Granite dust is more powdery and would contain some trace minerals in an unknown analysis. This could add soil minerals. The finer the dust the quicker it becomes available.

Sand, unless very fine powder dust would not add much nutrients, but can improve drainage and looseness in soil if enough is added, Sand is mostly silicon and if powder adds stalk strength if uptaken in the plant.

Decomposed granite is a rock powder and is an excellent amendment for clay soils. All rock powders are great sources of minerals and micronutrients. All growing soils need them. As the microbes and macrobes like earthworms, digest the insoluble minerals, they break down into the various soluble micronutrients that all forms of plants need.

For example, limestone rocks are rich in calcium. Granite rocks are rich in potassium, etc. Seaweeds of course are the king of micronutrient fertilizers and soil amendments. There can be up to 70+ trace elements in seaweed. In locations where seaweed is not readily available; rock powders is one answer to the problem.

Research continues to reveal that insoluble tiny particles like rock powder minerals, can be easily digested or absorbed via microbial activity, over time, into the anatomy of growing plants, thriving in the presence of rich organic compost, and other forms of powerful biostimulants like aerobic compost teas.

Obviously a heavy clay soil is very difficult to initially dig, whereas a sandy loam is much easier. Heavy clay soils can be improved considerably by adding a lot of sawdust and mason's sand. DO NOT use beach or river sand! Mason's sand, being crushed granite, has sharp edges and actually loosens the soil.

Granite dust and decomposed granite are essentially the same thing, although the size may determine what one is called. Decomposed granite is used most often as a base for stonework so the particles would be larger while granite dust particles will be much smaller.
Whether either one is a good soil amendment, is necessary, or is simply throwing your money away depends on what your soil needs. It can take the Soil Food Web many years to make the nutrients in granite dust available to plants.

What jonhughes said.
You could also search on "Azomite & Real salt", both are from UT.where they are mined from ancient seabed & volcanic ash. The Azomite is said to have over 60 trace minerals & elements.
That is close to seaweed & may have ancient sea weed in it.
Basalt dust is another name for granite dust.
You can search on Bio-char,zeolites, feldspar,Biotites, green sand,coir & gypsum also.

poaky, the feed store granite grit is just for porosity, something that all successful container growers aim for. Just make sure that it's not the smallest poultry grit, which can pack down like sand in a container.

John H.,
I have heard the expressions...builder's sand; coarse sand; mason sand, sharp sand, and other sands. I have used some masonary sand along with "gravel pit" sand. I wonder if masonary sand is usually just more finely screened sand in some cases. This whole sand thing has been confusing to me. I cannot say that I can see much difference in the end results.....but I have also mixed local spaghnum peat moss [90% and well hydrated] with sand in almost all cases.....wonderful results.

Okay so if I need to add trace elements I am better off using sea kelp? I say that because I can get it cheaper than DG.I don't know where to get DG locally anyway and shipping would be high (possibly) with the weight. I will use the granite chips for drainage. They range in size from a BB (gun pellet) to if you cut a baby asprin into 4 even pieces, it would be 1/4 of an asprin. And irregular shapes.I have added kelp to alot of my favorite plants area of the yard, but I need to create a mix for a large planter and it's for a indoor tree so will need to have a good bit of nutrients and good drainage. The tree will be Quercus Virginiana. I need to make a light but not too peaty potting soil.I have neptunes harvest almost a full bottle, is that as good as the powder? The bag I got and used up had more of either potassium or phosphorus than Neptunes Harvest.I was hoping that the granite would help acidify a couple areas too.I will try cottonseed meal or elemental sulfur. Which of the 2 is best? I am hoping for lasting results more than fast acting. The area will not be planted for a couple years, I'm building the soil with OM for a couple years prior.I'vr read that that will help alot but don't want the buffering to turn my soil back to 6.5, though not alkaline is not good enough for Pieris Japonica.

Out of all I wrote above I forgot to add my in-ground soil is well draining in this area,where I wanted to acidify.But anyway while researching this on the web I saw an article that some granite is releasing gamma rays and other harmful things,some of the sites had video from news stations and looked legit.There was testing done on some countertops installed in California that set of meters testing for this stuff, and those inhaling the dust are getting this stuff in their lungs.

Keep in mind that the people that want to sell you something will make amazing promises of things what they are selling will do. More often then not the product will not perform to expectations. There are a lot of people that swear that adding 1 tablespoon of Epsom Salt per gallon of water and then poured on their tomatoes will improve growth dramatically even though that will do very little in reality according to all of the research I have seen about that.

That's how myths are born. Pouring an Epsom salts (MgSO4) solution over your tomatoes can only help if A) there is a deficiency of Mg in the soil, or B) if there is so much Ca in the soil the plant is having trouble assimilating Mg (an antagonistic deficiency).

Al

Poaky - unless you use granite grit and other large particles as a LARGE fraction of your container soil, it won't improve the characteristics of drainage, aeration, and it won't change the height of the perched water table.

Think of stirring BBs into pudding. Will a handful of BBs in a quart of pudding make it drain better or increase aeration? NO You can't start with something like peat/compost/coir ... and increase the drainage or aeration by adding a small fraction of granite or any other large particles.

There is SOME benefit in adding these particles, though. They take up space then, that water an no longer occupy because they have no internal porosity. Essentially, when adding particles like perlite and granite to water retentive soils, all you're doing is reducing the amount of water the soil is capable of holding. The up side is that in decreasing water retention, air returns to the soil more rapidly. The down side is the PWT height remains the same ...... unless these large particles (usually in combination with other large particles, like pine bark) are a SIGNIFICANT fraction of the soil 60-100%.

You can learn a lot more about container soils by joining any one of dozens of conversations (or starting a new thread) on the Container Gardening Forum.

Al

Kimmsr & tapla, the myth with a grain of truth was started in the southern USA. We are nothing but a giant seashore/beach.
High in acid, low in Mg & Ca, & Epsom salt works great on all kinds of plants in these places. There are other ways of getting MgSO4, but Epsom salt is the easy way for most people.
As in, I never heard of stone/granite dust until I started reading Robert Rodale books on OG.
Like gypsum, Epsom salt has been over done, but both are good when use as & when needed.

Exactly - as/when needed .... not applied willy nilly in the hope that an excess will somehow make the plant grow better. An excess of an element can be just as effective as a limiting factor as a deficiency. If you have no reason to believe you have a Mg deficiency or an excess of Ca in the soil, you're better off to operate under the premise that applying Epsom salts w/o concrete proof it's needed, is more likely to be counter-productive than a benefit.

Al

Sandy soils: extremely likely that Mg, potassium, sulphur, B, and N at the least are too low.

According to things I have read lately lack of B causes a lot of problems, more than the land grants typically indicate. The land grants also pay strangely little attention to sulphur, maybe because sulfates are used a lot in conventional ag and/or because sulfur in the air pollution was heavy until 15-20 years ago. Even now in southern Ontario enough sulphur is in the air that it doesn't need to be added to ag soils, but many places now have too little.

So yes, epsom salt can be very helpful.

So can any one of dozens of other elements and compounds if the particular nutrients supplied are lacking - that is 'deficient', but if it is not a limiting factor, adding it over and above what the plant needs is counterproductive. It's not a difficult concept to understand.

Al

Think about this. If a soil has a nutrient deficiency and the recommendation to correct it is to add pounds of something per 1,000 square feet what would adding a tablespoon of of magnesium sulfate, mixed into one gallon of water, really do? Not enough to be of much value.
If a good, reliable soil test indicates there is a nutrient deficiency then work on making the soil, total, into a good, healthy soil that will grow strong and healthy plants and don't obsess about mixing magic elixars to change things.

I got it, Al. Comprendo that too much can be problematic. Too much of the macronutrients is uncommon in long-cropped land, though, or leachable soils.

Kimm, think about this: the building up of soil with OM has various limitations. I have been practicing explicitly just that for a dozen years at various sites. The OM itself can be and actually will be lacking certain minerals depending on the soils it is grown in. If one's general area is lacking macro and micro nutrients, and one's inputs are mostly made up of OM from the area, how are deficiencies going to not occur? For example, around here, as with most leachable soils, B is very low to non-existant. How am I going to build up B without adding imported borax? I think a lot of my problems with insects might be due to this and other deficiencies that are difficult to impossible to correct with my own compost or local OM. Manganese is another, the soils are very low. Where is it going to come from?

Maybe the bio-accumulators can do it, but so far that hasn't worked extremely well for me. Sandy soils especially are probably going to need to be artificially mineralized on occassion.

pubrown, search: Azomite,seaweed,Bio-char,Basalt dust, for more on macro nutrients.
I am going to do a few test beds this spring, I will post what I find.

Cool - I just didn't want people to walk away with the idea that dumping a water/Epsom salts solution on everything is going to improve growth. It CAN, but only under a very limited set of circumstances.

BTW - I agree with what you said about the limitations involved with depending entirely on OM as a cure-all for everything. OM is important to soil health, but it doesn't guarantee that there will/can not be deficiencies. Too much OM can also be a limiting factor.

Al

I have a test kit for the N-P-k it is a few years old. It's the capsules you mix with soil and water. As for micro-nutrients, if I add sea kelp can I be creating a toxic soil if the nutrients where okay before adding it? I am going to test the potted soil tonight. Drainage can be the second testing. I will add some sand (masonry, coarse)instead of the more expensive granite chips.I'll wait for feedback before adding more aggregate in case the masonry sand is a no-no. This is labeled all-purpose sand and added to cement powder makes conctete. There is no clay in my mix unless the bagged potting soil had clay in it.The potting soil I started with is the non peaty kind that is heavy and black.

I really think you're headed down the wrong trail, Poaky. Give the link below a read through & see if it helps you understand container soils better.

Al

Here is a link that might be useful: More about container soils