Soil test question

17 years ago

Hi all,

I'm a new organic gardener and I built beds based on the square foot gardening soil mix. I had samples tested by the local ext service. The PH levels were in the 7.9 range. It seems that I need to add sulphur. I have around 150 sq foot of veg beds. Any idea how to lower the Ph with sulfur?

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Comments (9)

justaguy2
17 years ago
What do you mean by 'based upon' the Square Foot gardening mix?

If your growing medium is made of vermiculite, compost and peat then the pH is most certainly not 7.9, it would be under 7.0. The extension service is wrong.

Did you use native soil in the mix? If so you pretty much screwed yourself by mixing something requiring improvement with something that doesn't (SqFt mix). The point of the mix in Sq Ft Gardening is to never have to fertilize or deal with pH in order to grow successfully.

Anyway, post back what is actually in those beds please.

Most likely you can offset the pH with more compost since it is such a limited volume of growing medium.
Kimmsr
17 years ago
Along with the test results from the Extension service should have been recommended quatities of "stuff" to add to correct the problems found from that soil test, ie. add X pounds of sulfur per 1,000 square feet to change the pH x amount. If it is not there you did not get a full report.
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timshaw
Original Author
17 years ago
I followed the recepefrom the book as close as I could. I used peat moss, vermiculite, mushroom compost, composted chicken manure and composted cow manure. I did not mix in native soil.
I had three beds tested and all were very alkyline am growing some vegs in one bed and scarlet clover in the other two. None of the plants look healthy, which is why I had the soil test done to begin with. Funny thing the report had sugestions but was only not to lime (that I could find ) The report has a numbr to call for info and I will call today.
Thanks, Tim
rhizo_1 (North AL) zone 7
17 years ago
Tim, be sure to tell whomever you talk to that yours is an artificial (soil-less) mix.
fertilizersalesman
17 years ago
4 pounds of sulfur on 150 sq feet will drop the pH to approx 6.5 in a soil with a typical CEC. If your soil is sandy use less, if it has a whole lot of sticky clay it may take more. It is best to till it in and will take several weeks to react.
timshaw
Original Author
17 years ago
Thanks fertilizersalesman,
What type of sulphur would you recomend I know of several types, aluminum sulphate, amonium sulphate. What type of sulphur were you speaking of.
Thanks, Tim
justaguy2
17 years ago
fertilizer salesman,

The mix in use is part vermiculite, part compost, part peat. I wouldn't know how to adjust the sulfur rate for such a medium.

I also can't fathom such a medium having a pH of 7.9.

My guess is Rhizo is hinting that the lab tests simply are not accurate with a soilless medium. It is the rare university set up to measure the nutrients in organic matter as well so the nutrient levels in the bed should *not* be added to based upon the lab results.

Honestly I don't think there is any value to a soil test when using a soilless medium. It is a different world.
rhizo_1 (North AL) zone 7
17 years ago
Not only will the soil test results be 'iffy', but the recommendations (as in pounds of whatever per 1000ft2) would be different, I would think.
fertilizersalesman
17 years ago
The sulfur I was refering to was just plain elemental sulfur. If you use aluminum sulfate you have to use 6.4 times as much.

This would not apply to potting media like peat. These materials do not have the same buffering capacity as soil and would require much much less to change the pH. I have had very little experience with soilless media, but enough to know that the pH and nutrient levels change very quickly. This is why most soilless production is under constatnt or near constant feed. I think soil tests for soilless media are good enough, particularly for pH, but I would expect the conditions to have completely changed by the time to results got back from the lab.