British Columbia: Rock Dust / Phosphate / Sulphate / Glacial Dust

I have been gardening with the Intensive, or Square Foot gardening method for just a few years now and am looking to keep the soil mix (which was originally made up of 1/3 vermiculite, 1/3 peat moss, and 1/3 five kinds of compost) with the right stuff. I would specifically like it if anyone can help me with the following information: Rock Dust.

My interest in rock dust started when I read Steve Solomon's recipe for "Complete Organic Fertilizer" from his book Growing Vegetables West of the Cascades. I thought this would be a good solution when topping up my raised beds each year. His recipe for the complete fertilizer is: 4 parts seed meal, 1 part lime, 1/2 part kelp meal and finally 1/2 part bone meal or rock phosphate.

So I call my local Buckerfields and ask "do you guys have rock phosphate?"... they respond with "We have Rock Sulphate." And to confuse me one step further my local nursery (small) has Glacial Dust from Gaia Green (link to that product, and product data sheet on that page) which I think some people may mistakenly call Rock Dust.

When I try to research these materials and their differences it would seem:

Glacial Dust is made up from "glacial moraine", or pulverized rocks left behind from glacial movement.

Rock Dust I'm assuming is the same as Rock Phosphate. Rock Phosphate is just ground up rocks- rocks that are supposed to contain 15-20% Phosphorite. Typical sedimentary rock contains less than 0.2%. This data is from this wikipedia page on Rock Phosphate.

Rock Sulphate is a mystery to me as I haven't been able to find out anything about it- which is entirely odd because you know the internet is all-knowing. Perhaps the employee at the store I called got it wrong?

I have no background in chemistry and perhaps that's why I'm not getting the difference between rock phosphate and rock sulphate.

So in order for me to find a solution for what to use in my veggie garden I look at it like this (warning: I am very inexperienced gardener):

Rock dust of any kind is used to contribute Phosphorus to your garden (as in the N-P-K Phosphorus) while Glacial Dust does not necessarily contribute Phosphorus to your garden, but rather contributes trace minerals to your soil. Glacial Dust is not a fertilizer or giving your plants "nutrition".

So my solution for now... I will add both! Some glacial dust as an aside from Steve Solomon's Complete Organic Fertilizer, and then the Rock Phosphate or Bone Meal to make up Steve Solomon's formula.

Does this sound like an OK course of action?

I will soon go to the store that quoted me they had "Rock Sulphate" and see what kind of packaging and info I can find out about that- but just avoid it for now.

Note: While I've read a little on Mycorrhiza I will not be adding any for now as I am planning on "fertigating" with my own garden tea made from nettles. Maybe next year I will add kelp and comfry to my nettle tea.

 

It's not a good idea to pour on mineral sources without knowing what is already in your soil. Look into sampling your soil and having it analyzed.

 

Thanks Ron B. Have had it analyzed. Low in nitrogen (got bloodmeal and nettle tea to help) and low in Phosphorus (hence my post). Looking to gain insight specifically about "Rock Dust / Rock Phosphate / Rock Sulphate / Glacial Dust"... and their application to my veggie garden.

 

If you want rock dust go to your local gravel crushing place and ask to clean up all the dust around the conveyers leading from the crushers. You can get it for free at the end of a shift. It should contain a wide variety of trace minerals and the recently crushed particles have sharp edges for the soil microbes to easily free up the minerals for the plant's consumption.

You want rock phosphate, not sulfate for phosphorous. I bought mine in 100 pound bags from Terralink Horticultural in Abbottsford. Bone meal works as well and is sold at reasonable prices at Terralink in 50 pound bags.

If you want to understand the role minerals play in soil, and how to get the perfect balance of minerals in your soil I recommend this book by Michael Astera. Steve Solomon approves as well (he commented on the book). See this link: http://www.soilminerals.com/Ideal_Soil_Main_Page.htm

 

Thanks Tree Nut! Good information.

Any idea on what the Rock Sulphate is?

 

I had never heard of Rock sulfate until you mentioned it. It appears that by exposing rock phosphate to strong acids, it mimics what soil microbes do as it converts the rock phosphate into a usable form that the plants can uptake. Basically converts hard rock phosphate into highly soluble 0-20-0 fertilizer.

"The acid treatment of hard rock phosphate converts many of the trace minerals in the hard rock to sulfate form. The result is a highly soluble source of phosphate and trace minerals, including calcium sulfate. Super phosphate is made from naturally mined hard rock phosphate and treated with sulfuric acid. The acid converts the hard rock to a powerful and soluble nutrient energy force that can really give plants a boost."

http://www.aglabs.com/newletters/tomatoes.html

 

What Tree Nut described is the production of superphosphate from rock phosphate. It has nothing to do with rock sulphate, which is still a mystery to me. Searching the Web turns up lots of suppliers of rock sulphate but not a single description of what it really is. Does anyone know?

 

Hi vitog... I'm most likely going to check out the shop this weekend, where the employee over the phone said they had Rock Sulphate. So hopefully I can report back next week as to what I've found out there. I'm of course wondering, with the lack of information on the internet, if the employee wasn't just wrong in what she said.