Acidifying soil for Blueberries.

charina(6b)February 20, 2014

I have a question (at the bottom) about how much elemental sulfur to apply. First, some background:

I have 20 blueberry plants on order, and need to amend my soil for them. I just received the results of my soil test, and I have (comparatively) good news! Only 7.4 ph, and 0.5% bicarbonates. That is great news for my neck of the woods (as far as blueberries are concerned) where ph typically is above 8 or 8.5, with bicarbonates comprising up to 20% of the soil!

Until I can amend the soil this summer and give the elemental sulfur time to work (or, more accurately, the bacteria to work on the elemental sulfur, and the resulting sulfuric acid to combine with carbonates to form gypsum), the plants will be grown in pots, with the soil treated with sulfuric acid prior to planting. I�m also setting up a venturi injector on the drip system to treat the high alkali secondary water provided here. Got that covered (at least in theory in my mind).

As I understand it, I need about 4.7 oz of elemental sulfur for each square foot of soil per each 1% of bicarbonates present in order to neutralize the bicarbonate�s buffering capabilities. So, with �% present, I should be applying 2.35oz elemental sulfur per square foot, right? Or am I working with incorrect information? If that�s right, I guess I�ll be needing a couple more of the 20lb bags to treat a 5x70 planting plot. 51 lbs total to neutralize the bicarbonates (5 X 70 X 2.35 divided by 16 oz per lb).

Now, how much elemental sulfur would be necessary beyond the buffering neutralization to reduce the ph from 7.4 to 5.5? I haven�t found information for that, and I�m hoping someone here has some info for me. I'm thinking I'll be applying 60 lbs total, retest, and see where I'm at by the fall, and irrigate with diluted sulfuric acid if necessary to to finish it off prior to planting.

Anything else I should be considering, or math corrections to be made? (and no, I don�t need a lecture about the dangers of sulfuric acid � I�m well aware and adequately prepared)

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fruitnut Z7 4500ft SW TX

Your number sounds low to me. Soil weighs somewhere near 100 lbs per cubic ft. That equals 0.5 lb bicarbonate per cubic ft. To figure sulfur you need to know the reaction equation and molecular weights. I figured that out once but don't have the numbers now.

The general feeling is that soils with free bicarbonate are very difficult to make and maintain acidic.

I'd be thinking about making a raised bed about 18 inches deep and filling it with an acidic mix probably mostly spaghnum peat moss. This sounds a lot easier than amending the native soil.

My soil has little to no free bicarbonate and pH around 7. I'd still do the raised bed.

This post was edited by fruitnut on Thu, Feb 20, 14 at 16:56

    Bookmark   February 20, 2014 at 4:11PM
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drew51 SE MI Z5b/6a

My soil is at 6.5 and it was too hard to maintain so I too have raised beds. In ground the surrounding ground quickly neutralized my soil. I could not keep it low enough. 12 inches high seems good enough. Working for me. You will have an island of acidity surrounded by alkalinity in ground, it may last two years before you'll need to add just as much again. Probably only one year.

This post was edited by Drew51 on Thu, Feb 20, 14 at 17:01

    Bookmark   February 20, 2014 at 4:52PM
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Thanks for the thoughts.

FN, I did a little more looking around the web and found:

Clemson UâÂÂs Jim Camberato, in reference to turfgrass indicates âÂÂEach 10 pounds of elemental S generates enough acidity to neutralize 30 pounds of limeâÂÂ. That is 5.33oz sulfur per 1 lb lime.

Utah State, (multiple contributors) in reference to blueberries indicates: âÂÂOne percent lime is equivalent to one pound of lime per square foot, and would require nearly a pound of sulfuric acid, or 4.7 ounces of elemental sulfur per square foot, just to neutralize the lime.âÂÂ

British Columbia Ministry of Agriculture states âÂÂGenerally, elemental sulfur when fully converted to sulfuric acid will reach with threefold its applied weight of residual limestone.â 16 oz/3 = 5.33 oz per 1 lb lime.

Also of note in the BC fact sheet is the following: âÂÂMixing acid sphagnum peat at a 1 to 1 volumetric ratio will neutralize the residual carbonate in a soil that contains 1% calcium carbonate equivalent.âÂÂ

The consensus seems to be around 5 oz sulfur per 1lb carbonate. I was working off the USU info, which is the lighter, but seemingly more precise, ratio.

    Bookmark   February 20, 2014 at 6:19PM
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Drew: Did you do anything to treat water being applied to your ground? Use rainwater? Just wondering if that could be a contributor to your experience as well as leaching from surrounding (or subsurface) soils.

I'm not thinking that leaching would be as large of an issue here in UT as it may be elsewhere. Less than 15 inches of rain a year, so the soil is very dry most of the year unless irrigated. I suspect, but don't really know, that dry conditions would prevent horizontal chemical/ion transfer. And almost all of the 15 inches comes in the Spring, having a flushing effect on my slightly loamy sand when it does come.

From what I've read, recommendations are for lesser amounts of 'maintenance' application of sulfur or sulfate product annually. I'm having a hard time wrapping my mind around a need to apply the same amount annually. Esp if the buffering capacity is the primary issue upfront.

Honestly, I think my irrigation water is going to be a larger issue than the soil. Raised bed, pot, or amend my sand, the water is going to ruin it for BB's if I don't get that under control.

    Bookmark   February 20, 2014 at 6:33PM
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fruitnut Z7 4500ft SW TX

You're right about the water. I do really well with rainwater. But even that's only easy for potted plants after about two yrs. Get them that far, growing well, and at the proper pH and after that you're home free. I haven't found a need to repot even after 7 yrs.

This is an interesting and fun project. What I don't know is how uniform the resulting pH would be both across the bed and with depth. Not much good if the surface is pH 3 and deep still 7.4.

What I'd expect is a minimum of 2-3 yrs to get to an acceptable condition. And then the pH might change going forward. Probably drifting back above 7. So get those pots going. That's still the easiest way for us with high pH soils.

    Bookmark   February 20, 2014 at 9:10PM
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I too doubt you can amend soil enough to get it to produce a pH5 and maintain it for blueberry production. But you can certainly readily grow them in containers with acidified soil. But the 3 yr. old plants (largest ones offered, sometimes "3 gal.") so they will bear that year.

Here is a link that might be useful: Blueberries in Utah? Difficult, but Maybe Not Impossible

    Bookmark   February 20, 2014 at 9:36PM
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drew51 SE MI Z5b/6a

"Drew: Did you do anything to treat water being applied to your ground? Use rainwater?"

I use rainwater, and use sulfuric acid if I need to use tap.
It didn't help. In the raised bed, starting with a lot of peat. I prepared the summer before, added sulfur too. In the next spring I planted into the beds. They are doing great! I monitor PH and it's super easy to keep PH low. it's staying low. I also use Ammonium sulfate. Plants are mulched with pine bark, and also have some pine needles.
In ground the PH was good, but then slipped back, and I just could not catch up, probably if I amended the ground better with peat. I did amend, but mixed with native soil. Probably a mistake.
You do get a lot less rainwater, we get over double that.
I might have been able to do it in ground, but I just saw the plants struggling and had to do something. So the first winter 2 remained in the ground (all I had). Last year I added a third plant. I built three 4x4 raised beds. I also grew strawberries around the periphery of the beds. If the PH is wrong it really sets them back. They are doing really well in the beds. I'm adding three more this spring, but I decided to grow them in pots this time.

Well you can try it out it may work. If it doesn't you can opt for raised beds. You can move the plants into the beds. I didn't have a problem transferring plants.
Keep us updated on progress. It's nice when people share what they learn, we all get a little better at this lifelong study of gardening.

    Bookmark   February 20, 2014 at 10:46PM
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Thanks for the link Fascist_Nation. I don't have it as bad as much if UT fortunately. If possible at all in UT, I have as good of starting soil as possible, so a decent chance for success. Perhaps it will be the fall of 2015 or spring 2016 before I consider putting them in the ground. In the mean time, I think I sense a desire to try to prove it possible and overcome. I will see if I can get proper ph in the soil before moving them out of pots. If not, then pots for life it is.

    Bookmark   February 20, 2014 at 10:54PM
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You are right that you have it good for Utah. I don't know what the total % bicarbonates are for my soil but with how hard the irrigation water is and how much fizzing I get when I add just a little bit of soil to an acid like vinegar I always assumed it had to be at least 20% or more.

I've heard of someone running a blueberry farm in northern Utah around Logan. I bought some blue berries last year from a fruit stand that said they were local so I really picked their brain for the details. Anyway the guy said they grew them in rows in a deep layer of mulch on top of the soil. Then they would acidify the irrigation water with sulfuric acid, so it is possible.
To me a deep layer of mulch is no different then a raised bed or containers.
Have you decided on how to acidify the irrigation water? Most people use sulfuric acid while others don't feel safe messing with it. I personally wouldn't mind using it but you do need to know what you are doing. As an alternative that I have wondered about, I am borrowing this idea from the aquarium guys, is using a water softener with potassium chloride instead of sodium chloride. That way every time you water you are fertilizing the plants but I don't know if it is too much potassium.

    Bookmark   February 21, 2014 at 10:47AM
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Drew51 wrote:"I use rainwater, and use sulfuric acid if I need to use tap. It didn't help."

Thanks for the additional details Drew.

    Bookmark   February 21, 2014 at 10:47AM
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I grow blueberries here in Madison, Wisconsin, in our native soil, amended with either peat moss or compost made from shredded tree leaves. Agricultural sulfur is used to lower soil pH. The starting pH is 7.6, and that is also the pH of our local water supply, supplied by the city of Madison, from local wells. There is a lot of limestone here, most of it is underground, and that is where the aquifer is found. When planting a blueberry shrub, I dig out a "V" shape hole, and I put 6 ounces by volume of agricultural sulfur in the very bottom, where it is left, undisturbed. This is done in order to prevent the local soil from raising the pH around the blueberry roots. The hole is filled about halfway with peat moss, and an equal amount of our local dirt is added in. The two are mixed by hand, which takes some effort. You have to break up all the clods and clumps. The shrub is planted, watered in immediately, and another 6 ounces by volume of agricultural sulfur is put down on the surface, in a ring. This is covered with mulch, and more water goes down. We do not have a rain barrel, so cold tap water is used on the blueberries. I am able to maintain soil pH between 4.0 and 5.5, with agricultural sulfur. The pH is tested once a year, or maybe twice a year, if there is a problem or concern. I used to use a pH meter, which works OK, but the meter lasted 3 years before it died, so I looked for a less expensive method. Finally I settled on indicator dye solutions. These indicators have a long history, they are the original method for measuring solution acidity, used before the pH scale was invented. They are reliable and easy enough to use, but they are not as precise as a calibrated pH meter. Using bromocresol green, my test result might be pH = 4.6, plus/minus 0.2. So the actual pH could be 4.4, 4.5, 4.6, 4.7, or 4.8. I generally plant blueberry shrubs in the spring, as soon as the ground can be worked. I have also planted them in the fall, in mid September. I prefer to plant potted shrubs, because I have had problems with bare-root blueberry stock.

    Bookmark   February 21, 2014 at 10:53AM
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Good reminder Greg about building up a row with mulch. That is part of my plan, but I forgot to detail that above. I grew up in OR, and used to pick many many lbs of blueberrys from the Upick farms every year. Most of the farms use rows of built up mulch even with the more favorable soil.

At this point I do plan on using sulfuric acid. I have my 98% acid on hand - just arrived yesterday. My mental plan is to mix up diluted batches in a 55 gal barrel (so I don't have to don the full protective gear so often when dealing with the concentrate - will still use gloves, face protection with the dilute, but perhaps not the boots, apron, etc), and then use a Mazzei venturi injector to pull this diluted (but still rather acidic) mix into the distribution line as part of the drip irrigation system. If I had to do this by hand mixing and hand watering all summer, I wouldn't be willing to bother. But being able to semi-automate it, I think I'm game.

It's going to take some fiddling to get the ph on the water right. Trial and error adjusting a bypass valve and pickup tube valve. See Mazzei Brochure for an example of the setup. But, after a roll or two of ph paper, I should be able to figure something out that is largely repeatable as long as I mix the dilute solution the same each time.

Perhaps in a year or two, if the funds are there, I might consider a dosamatic or dosatron. But for now, I've already spent more than I should have on plants and pots, so such an upgrade will have to wait.

    Bookmark   February 21, 2014 at 11:21AM
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Thanks for the experiential input eric! Interesting spatial application of the sulfur. It makes theoretical sense to me.

I think I'm going to have to give the addition of peat more consideration given al the various input.

    Bookmark   February 21, 2014 at 11:42AM
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fruitnut Z7 4500ft SW TX


If you want private email exchanges thru gardenweb, you need to enable that on your member page.

I don't know of a source for any type acid other than sulfuric and I've only bought battery acid for that. You might try a separate post here.

    Bookmark   February 21, 2014 at 11:42AM
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That is a great plan for mixing the acid and I would love to see what your end set up looks like! I bought a few used 55 gallon plastic drums on KSL last year for about $20 each so they a reasonably priced and easy to find. Keep us posted.

    Bookmark   February 21, 2014 at 11:45AM
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alan haigh

OK, I keep saying this, and I guess it will never penetrate, but blueberries can thrive in soil in the low to mid 6's pH in mulched soil that is well drained with ample OM content. Also the soil never needs to be uniformly acidic as long as a portion of the root system can access the iron it needs.

Lots of people grow blueberries around here that don't acidify their soil and I often come to sites where such plants are thriving and bearing heavily in soils that are close to neutral. It's funny how often reality defies the book when you get to study the results of projects that don't follow guidlines.

My theory is that mulch releases acids as it breaks down that release enough free iron in the interface, where feeder roots flourish, to keep plants healthy.

I'm not saying this would work where the irrigation water has a pH of 8 (Bamboo Rabbit has this covered by adding steady amounts of sulfuric acid to irrigation water) but at least you should know that you don't necessarily need to maintain a pH between 4.5 and 5.5 to grow productive blueberries.

Use your peat moss liberally, use raised beds if you've fine soil. and mulch with coarse wood chips and plants will do fine in a rather wide range of pH.

    Bookmark   February 21, 2014 at 11:49AM
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drew51 SE MI Z5b/6a

Well it certainly looks like it can be done. With lot's of sulfur! I prefer the raised bed where I'm using a minimal amount of sulfur as the bed maintains the PH well.
I like the idea of minimum care as I have a lot of other plants to tend to, too. They are growing like crazy, they love it. I suspect container culture will be just as easy.

Harvestman, my experience is different, mine would not grow in a PH of 6.5 . Why I went to raised beds. I gave it a season and the plants did nothing. Plus I did use rainwater, peat, mulch, didn't help. Some cultivars may be better than others? I do know they grow like weeds in soil with a ph of 5 or lower. All gardening is local I guess? I tried and give up growing in ground. Maybe my PH was actually higher than I thought?

You can buy full strength sulfuric acid on Amazon.

This post was edited by Drew51 on Fri, Feb 21, 14 at 12:42

    Bookmark   February 21, 2014 at 12:31PM
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alan haigh

Drew, did you use the same plants in the new environment? Blueberry plants get stunted for a variety of reasons- pH issues may be evident by chlorosis but poor drainage can cause the same symptoms.

A short period of spring drought probably stunts more blueberries than anything else. Their non-fibrous roots are terrible at pulling water from soil when they are young. To me they are the most difficult of plants to get off to a good start, whatever the pH. That's why I stopped growing them in my water starved nursery in spite of good demand.

Someone who used to post here told of starting his plants in 5 gallon pots of mostly ground pine bark fortified with time release fertilizer with a drip system that gave them water every day. The plants were well branched and over 5 feet tall after one season, starting as typical 12" bare root starts. If I was starting a large project I might use his method. I did not believe him at first but his photographic evidence was completely convincing- after a few posts you could tell he was honest anyway.

At any rate, raised beds are recommended for blueberries even where pH is low and soil reasonably coarse.

I've never seen any research that indicates the importance of the lateral movement of calcium but it is an astute and logical theory IMO.

    Bookmark   February 21, 2014 at 1:23PM
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Charina, I am guessing that you already know this, but I will re-state anyway, just in case: If you add concentrated sulfuric acid to water, the heavier acid will descend, and mix with the water on the way, with no frothing or bubbling. So, this is the correct procedure, adding acid to water. If you forget, and add water to concentrated sulfuric acid, the lighter water will float on top, and there will be steam generated at the interface, the surface where the acid and the water are in contact. If the container has a narrow neck, the steam will likely lead to a geyser of acid and water that can spray for perhaps 30 feet in every direction. So, adding water to concentrated acid is to be avoided.

    Bookmark   February 21, 2014 at 1:57PM
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drew51 SE MI Z5b/6a

"Drew, did you use the same plants in the new environment?"

Yes, they responded in the beds. It could have been drought? Two plants also suffered a set back when my dog who was like 3 months old chewed them to one stick! Argh! They recovered, but one was so bad, I was not sure it was alive, it was, and grew 4 new branches. They grew a good 2 feet. I have three more coming, but will keep them in pots. I don't have any room for more beds, well I need room for other plants and stuff. I plan to grow a lot of peppers and tomatoes next year. I've been getting into them, peppers are awesome beautiful plants. Perennials too, you can keep some for years. I plan to set up a grow room for them. Mostly just for ornamental reasons than peppers, beautiful purple and variegated foliage. Any fruit is just a bonus.
Anyway good luck charina, sounds like you did your homework, and I can see this working well.

    Bookmark   February 21, 2014 at 2:15PM
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Eric: Yes, I do know, but it is a good reminder for anyone reading this thread that it is not a good idea to play with acid without proper precautions and understanding. It would be all too easy to become blind making a thoughtless error like wrong mixing order.

HM: I've read many of the threads on here re blueberries, and your comments re neutral or near-neutral soils with high OM have been noted (at least by me). Your theory of zonal variation seems to have merit. Makes me want to plant a few plants in a hole with one side native soil, and just off to the side in the opposite direction some peat/acid amended soil. See if even with majority of roots in 7.5 ph soil they can thrive. Eh, I'll save that for some later year of investigation.

While you are in Z6, by chance are the bushes you observe largely Southern? Conventional wisdom indicates they are more tolerant of higher ph. Of course, the plants don't read the books, or the forums, so whatever works despite what is written is what's best.

I recall the thread, and the discussion with the 1,000 or so plants you are referring to. Part of my plan, starting with pots this summer is influenced by that thread and your comments about it in a later thread. And hence my decision to modify my irrigation to go with drip rather than try keeping on top of it by hand.

Re neutral or near-neutral ph soils with lots of OM, it could be that in your area the soil is more consistent, and the OM is just enough to modify. I know that in some areas of the country, while the surface soil may be neutral, sublayers are highly alkali. Makes me curious about Drew's experience if there is soil nearby that was strongly influencing ph even though tested areas were reasonable ph.

    Bookmark   February 21, 2014 at 2:23PM
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alan haigh

Charina, I've never grown a rabbiteye blueberry until last season where I planted a Pink Lemonade for a client because he enjoys some novelty. They are also supposed to be very sweet.

I suppose you read the older thread that has popped up next to yours. The author's thread grows rhododendrons in near neutral soil that are exceedingly vigorous- he mulches them.

I can't blame anyone for questioning my "alleged" anecdotal observations. I just searched the web for any research that might confirm my experience and every single source I could find in a 30 minute search suggested any pH above about 5.3 would be highly detrimental. It is so widely accepted I don't even think anyone has done any research on it for decades- I could find no actual research on the issue at all.

    Bookmark   February 21, 2014 at 4:21PM
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drew51 SE MI Z5b/6a

Makes me curious about Drew's experience if there is soil nearby that was strongly influencing ph even though tested areas were reasonable ph."

I beginning to think my readings were wrong. I will retest this summer in various spots again. We do have clay loam, below the loam is pure clay for about a foot, then under that is a clay-sand-loam. My blueberries are all NHB, though buying three SHB for pots.

I'm planting a lot of plants in ground, so I'll test each area.

    Bookmark   February 21, 2014 at 4:47PM
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alan haigh

Should have said the thread's author not the author's thread. Too much time at the computer today- tired of trudging in snow but it keeps me closer to sane.

    Bookmark   February 21, 2014 at 5:46PM
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drew51 SE MI Z5b/6a

Maybe you should just buy bundles of peat and call it a day!

    Bookmark   February 21, 2014 at 11:12PM
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alan haigh

Yeah, I love that method. Dissolve the fertilizer in the water you give the plant and make sure the peat doesn't dry (or get too soggy) out and I guess you are good to go- as long as you've got some neutral water. That's where a good cistern comes in handy. I've got one with about a 500 gallon tank- int the west you'd need four times that capacity.

    Bookmark   February 22, 2014 at 6:51AM
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