Will Growing Conifers (pines, junipers, spruces, and others) Acidify Soil

If you look around on the internet you can find quite a few "sources" that say that growing members of the Conifer family of trees will effectively cause a rise in soil acidity.
The Big question is "Is that really true?" The smaller question is "by how much will the soil acidify and how long will it take for that acidification to occur?"

So what we first need to understand is what is soil acidity and how does nature create acidic soil that will still support plant life.
Soil acidification is the buildup of hydrogen cations, which reduces soil pH. Chemically, this happens when a proton donor gets added to the soil.
The donor can be an acid, such as nitric, sulfuric, or carbonic acids. It can also be a compound such as aluminium sulfate, which reacts in the soil to release protons.
Acidification also occurs when base cations such as calcium, magnesium, potassium and sodium are leached from the soil.
Soil acidification naturally occurs when lichens and algae break down rock surfaces.
Acids continue with this dissolution as soil develops.
With time and weathering, soils become more acidic in natural ecosystems.
Soil acidification rates can vary, and increase with certain factors such as acid rain, agriculture, and pollution.

Rainfall is naturally acidic due to carbonic acid forming from carbon dioxide in the atmosphere.
This compound causes rainfall pH to be around 5.0-5.5. When rainfall has a lower pH than natural levels, it can cause rapid acidification of soil.
Sulfur dioxide and nitrogen oxides are precursors of stronger acids that can lead to acid rain production when they react with water in the atmosphere.
These gases may be present in the atmosphere due to natural sources such as lightning and volcanic eruptions, or from anthropogenic emissions.
Basic cations like calcium are leached from the soil as acidic rainfall flows, which allows aluminum and proton levels to increase.

Plant roots acidify soil by releasing protons and organic acids so as to chemically weather soil minerals.
Decaying remains of dead plants on soil may also form organic acids which contribute to soil acidification.
Acidification from leaf litter on soil is more pronounced under coniferous trees such as pine, spruce and fir, which return fewer base cations to the soil, than under deciduous trees

Certain parent materials also contribute to soil acidification.
Granites and their allied igneous rocks are called "acidic" because they have a lot of free quartz, which produces silicic acid on weathering.
Also, they have relatively low amounts of calcium and magnesium.
Some sedimentary rocks such as shale and coal are rich in sulfides, which, when hydrated and oxidized, produce sulfuric acid which is much stronger than silicic acid.
Many coal soils are too acidic to support vigorous plant growth, and coal gives off strong precursors to acid rain when it is burned.
Marine clays are also sulfide-rich in many cases, and such clays become very acidic if they are drained to an oxidizing state.

Conifers do like acidic soil in the range of 5.0 to 6.5 (depending on species) and the root systems of the junipers and some of the long leaf pine species can make an adjustment (over a period of 2 to 10 years) of one full pH point.
Spruces tend to make less of an adjustment in the same time period when compared to the above junipers and long leaf pines.
The real adjustment comes from 1. root exudates that attract fungi and bacteria that break down calcium containing mineral compounds, the calcium is used by the trees and that changes the ionic makeup of the soil, turning it more acidic.


It doesn't really help that there is so much misinformation being put forth as truth, even by some Horticulturist.

Myth number one is that adding sphagnum peat moss to your garden beds will acidify the soil enough that you could grow blueberries, which like their soil to be in the 5.5 pH range.
While this particular item will indeed lower the pH of the soil, it only happens for a fairly short period of time and you will need a minimum of 2 inches depth of this material worked into the soil for the effect to last around 10 to 15 weeks.
The pH adjustment of such an addition will be in the 0.2 neighborhood. That means that if you want to lower the pH from 7.0 to 6.8, your good to go, but most of the time we don't have a perfect neutral pH soil.
If you have soil with a pH of 8.0 you would need 10 inches depth of sphagnum peat worked into the soil to get the pH down to 7.0, and you would then need another 2 inches to get to the goal of 6.8, so 12 inches of sphagnum peat moss laid on and then worked into the soil.
And the effect of using all that peat in your soil would last effectively for a maximum of one growing season, not a very good return on your acidification efforts it would seem.

I'll be back with the rest of this story as soon as I can.

Redhawk

Back to the members of the conifer family of trees.

Since we know now that soil acidity can be thought of as a lack of base cations and we know that conifer trees soak up the minerals calcium, magnesium, potassium and sodium and we know that tree leaves (needles) and dead branches do not readily give up these minerals, we can see how conifers can, over a vast period of time, create an acidic soil condition.
The main problem is the amount of time these trees have to grow in order to create an acidic soil condition.
Currently a study was completed that started in 1970 with the planting of a large grouping of pine trees on land that was tested and found to be nearly neutral, just leaning to the basic side of the fence by 0.1% (7.01 pH)
The trees grew for 30 years and then soil samples were taken to compare with the original set of data taken just prior to planting of the trees.
The results were not what the researchers expected, the soil had barely moved towards acidic (from 7.01 to 6.986 pH) an approximately .2 change in pH over a 30 year period.
There is another study going on now and it is along different lines, this study is looking at the stability of soil pH in a conifer forest that is mostly older growth (90+ years).
This study was begun in 1968 when the forest was already at least 40 years old in new growth, the soil is a granite base and the initial data showed an overall average pH of 6.3
The latest data was taken in 2014 and the pH was an astounding 6.255, not much movement from detritus or rain fall.
The overall picture is looking like conifer trees are great at holding the pH of their soil very steady. I am searching for someone who has one of these studies going on in Michigan, near the great lakes, that area is one of the heavy "acid rain" areas in the USA.
I am wondering if the conifer trees are able to buffer soil that sees a lot of acid rain thus keeping the acidity of the soil as stable as they do on the West Coast.

Ways to acidify soil for growing the plants that require acidic soil (blueberries, etc.)
In small garden spaces or containers the peat trick does work but mostly because you are going to replace the soil at least every two years.
In large garden areas we have some better options; Liquid ammonia that is diluted 5 to 1, Vinegar diluted 100 to 1, mineral dusts (granite rock dust), Citric (acetic) acid, Nitric acid, Sulfuric acid, Carbonic acid, all will do the job as long as they are highly diluted (2 TBS per gallon)(always add acid to water, never water to acid).
Sulfates will also acidify soil and are easy to apply when the sulfate is in powder form, just dust the soil surface lightly.

So there you go, can you acidify soil by growing conifer trees? well, not really but you can keep that soil at the acidity level you want by having them growing in that area.

Redhawk

(If you want the references, let me know, there are quite a few)

I was always cautious with people suggesting things like adding pine needles for blueberries. It's recommended a lot. It never really made sense in my mind. When you look at acids they want to fizz out. Pour it on the ground and how long does it stay an acid? Not long. Its like an acid doesn't want to be an acid,  so it eats stuff til its not. So a little bit of needles added on a lot of soil is gonna fizz out fast.

That was my simple reasoning and may be wrong scientifically, but luckily the answer may have been right.

You are mildly missing the point.  The soil is what matters.  For example where I am is calcite bonded shale under clay.  You mostly can't throw enough acid at it to make a serious change.  You can buffer it with organics and bring it down from mid to high 8's down to mid to high 7's.  And someone on limestone soils will have to try harder still.  Here the answer if acidic soils are needed is you do a raised bed and then keep throwing acid at it to compensate for the irrigation water that is slightly basic having arrived after running thru 35 miles of canal system in basic soils.  The smarter answer is to accept high pH soils and choose the plants that will work with them.

I do not think the idea will work very well.

In my forestry plan for my farm, I have a list of tree species that I should target based upon the soil in that particular stand. It stands to reason, trees will only thrive where they are getting the nutrients that they love.

To me, it would be kind of silly to plant a type of tree in a radically different soil than what it likes, to try and change the soil. It would be the equivalent of sending children to a senior citizen's center for a day care center to improve the morale of the senior citizen's living there; the site just not match the needs of the children. I am pretty sure the senior citizens would not enjoy the experience much either.

Why try and constantly battle nature? That is what conventional farmers do, and wonder why they are not very profitable (as my own family does).

wayne fajkus wrote:I was always cautious with people suggesting things like adding pine needles for blueberries. It's recommended a lot. It never really made sense in my mind. When you look at acids they want to fizz out. Pour it on the ground and how long does it stay an acid? Not long. Its like an acid doesn't want to be an acid,  so it eats stuff til its not. So a little bit of needles added on a lot of soil is gonna fizz out fast.

That was my simple reasoning and may be wrong scientifically, but luckily the answer may have been right.

That is not the way it really works.

The PH levels in soil constantly change. When I first convert forest into field the PH is incredibly low, and with so much woody debris in the soil, it is consuming vasts amount of nitrogen to break down the wood debris. I can combat this with heavy doses of nitrogen in order to get my crops to grow, but thankfully it is short lived. And the PH levels change as well.

Adding pine duff to blueberries works the same as adding fertilizer to your garden; it gives immediate results. How much a person adds depends on their level of PH, just as how much fertilizer is needed for a garden is based on the NPK and major and minor nutrients.

I live in the blueberry capital of the world, and do so because of the low PH levels here. But a person with high PH levels will have to add an awful lot of pine duff every year to get good growth results.

But C. Letellier has got the honest answer: why try and battle nature?

I have said that for years. Because of our low PH levels, we can grow blueberries, cranberries, potatoes and pasture grass really well here, but for some stupid reason, the potato farms have converted to dairy farms where they are trying to raise alfalfa and corn that require ample inputs of lime to increase our PH levels, and wonder why they are struggling fiscally. When I suggest they should at least add sheep to the profit line as we have ideal pastures here, they act like I am stupid.

The question is not if adding pine duff works, it is how much pine duff does a person want to add, and for how long?

But that is not the orginal question. That question is, will planting softwood trees enable the ph to remain lower, and the answer is, the trees will probably not survive to do the soil any good.

This is interesting, and good to know.

I definitely have to acknowledge the wisdom of the points made by C. Letellier and Travis. Why fight what you have? Doesn't alfalfa grow well in slightly alkaline conditions? I know that in the right conditions, it can send taproots down like 6 feet or more. Don't asparagus also like it a bit alkaline?

I think that in that situation, I would probably grow as much of whatever would grow well as possible, chop-and-dropping regularly, pasturing animals on it if possible. The added organic matter would increase the available options.

I think that if I had garden vegetables or crops I was growing on a limited basis, I would do them on hugelbeets.

What I wonder though, kola Redhawk, is if there are things we can do to enhance the capacity of conifers to acidify the soil. If a copse of conifers, an island of acidity in a sea of alkali, were supplemented with all they needed, would they acidify the surrounding soil, and is there anything that could be done for them, any system put in place or supplementation, that would make them better able to change the surrounding soil to their needs?

I mean, if we had that theoretical copse, and in addition to regular root-zone sub-irrigation, they were fed with, dissolved in their irrigation water or topdressed or whatever, any mineral and/or nutrient precursors necessary for soil acidification, and if they were regularly doused with oxygenated compost extract and fungal slurry, what are the odds that the copse's capacity to acidify the surrounding soil would increase?

-CK

Chris Kott wrote:This is interesting, and good to know.

What I wonder though, kola Redhawk, is if there are things we can do to enhance the capacity of conifers to acidify the soil. If a copse of conifers, an island of acidity in a sea of alkali, were supplemented with all they needed, would they acidify the surrounding soil, and is there anything that could be done for them, any system put in place or supplementation, that would make them better able to change the surrounding soil to their needs?

I mean, if we had that theoretical copse, and in addition to regular root-zone sub-irrigation, they were fed with, dissolved in their irrigation water or topdressed or whatever, any mineral and/or nutrient precursors necessary for soil acidification, and if they were regularly doused with oxygenated compost extract and fungal slurry, what are the odds that the copse's capacity to acidify the surrounding soil would increase?

-CK

Since we know that conifers will at least keep the soil pH near the range it starts at if we make a soil pH adjustment at or just before planting a grove of conifers, we will enable the conifers to be maintainers of that adjusted pH.
Making sure we have the right negatively charged atoms and molecules in the soil would then be the method of helping maintain the pH.

As Travis brought up, (good job) pH will move up and down with the seasons and by all the plants growing in any specific area, so by adding buffer plants we can make those pH movements smaller.
Both Travis and C Letellier brought up the "grow what wants to grow" idea, which is exactly what people should be doing, mimicking nature is always going to work best and cost less than trying to make any soil extremely different from what it was in the beginning.
The only time this principle should be ignored (but not completely) is when we are doing remediation work to restore land to what it was before man's meddling screwed it up.

Redhawk

Chris Kott wrote:This is interesting, and good to know.
... Doesn't alfalfa grow well in slightly alkaline conditions? I know that in the right conditions, it can send taproots down like 6 feet or more. Don't asparagus also like it a bit alkaline?

I think that in that situation, I would probably grow as much of whatever would grow well as possible, chop-and-dropping regularly, pasturing animals on it if possible. The added organic matter would increase the available options.

I think that if I had garden vegetables or crops I was growing on a limited basis, I would do them on hugelbeets.

What I wonder though, kola Redhawk, is if there are things we can do to enhance the capacity of conifers to acidify the soil. If a copse of conifers, an island of acidity in a sea of alkali, were supplemented with all they needed, would they acidify the surrounding soil, and is there anything that could be done for them, any system put in place or supplementation, that would make them better able to change the surrounding soil to their needs?

I mean, if we had that theoretical copse, and in addition to regular root-zone sub-irrigation, they were fed with, dissolved in their irrigation water or topdressed or whatever, any mineral and/or nutrient precursors necessary for soil acidification, and if they were regularly doused with oxygenated compost extract and fungal slurry, what are the odds that the copse's capacity to acidify the surrounding soil would increase?

-CK

First off alfalfa and asparagus do at least okay in alkaline soils.  We grow both here.  The native soil pH in this area runs 8.5 to 8.8 typically with a few low organic low areas go 9.2 to 9.3.  Alfalfa is grown commercially all over here because of our very dry summers.  And I am aware of one clump of asparagus growing on a dry shale/clay point over a canal that is nearly 10 feet above the water line.  Someone obviously planted it there when the water line was much closer and as the canal has cut down the roots kept chasing the water until this clump is growing in what looks like an impossible location.  The point though is that point has virtually no organic to it so the soil pH will be at least 8.5.

Organic matter always buffers pH.  And that is both acid and base.  In general adding organic will move the soil closer to 7 in most cases.  In my area a large load of organic usually make 1 point difference or slightly more.  So for example my soil (aka raw clay) with 8.8 native soil pH will finish with about 7.5 to 7.8 with lots of organic worked in.

If you want to try acidification with evergreens I might have some help for you.  Most evergreens want an acidic environment and won't handle base well so your choices are limited.  Wanting them for winter wind breaks over the last 30 years  I have spent lots of time and money on chemicals trying to grow them here.  The hard lesson that came out was grow what grows.  I have killed many hundreds of trees over decades learning that lesson.  Since my soil is clay, high salt and high pH the choices are very limited.(PS I am US grow zone 4 borderline zone 3)  So far I have 3 evergreens that are making it in my ground.  Austrian pine works, Colorado Blue spruce works and a couple of varieties of juniper.  Now supposedly white pine, eastern red cedar and lodge pole are supposed to work too but I have killed all of them on a regular basis.  Eastern Red cedar I am told is dying from salt damage.  White pine and lodge pole  simply fail to thrive and sit there and slowly die with one needle at a time turning yellow and falling off till I am left with a stick(some of my sticks have existed for years before the last needle falls off).  Potted Colorado Blue spruce typically sits there for several years to a decade growing very little.  Finally one day they seem to simply give in and decide to grow there because it is their only choice.  Austrian Pine likes a bit of a sandy area created to help it get started but seems to do okay allowing for the fact that growth is slow.  My nearly 20 year old Austrian pine is all of about 10 or 12 feet high where the books say it is supposed to do 2 feet a year.  The roots do extend out into the clay but my survival rate is way better if I do a shallow backhoe trench and back fill it with sand.

As for acidifying the ground if you want to work at it I am sure it can be done.  Just remember that most likely you are in this as a battle for a long time.  The easy example would be make vinegar.  And you wouldn't even have to distill it to concentrate it because nature would do that for you in most areas.  Simply pour it on the ground.  I seem to remember someone saying comfrey tea was slightly acidic so that might be another possible.  And almost anything that is acidic by nature should help.  Maybe you grow a whole lot of something like tomatoes that are high acid by nature and compost that on top of the soil you want to acidify.  I am sure there are organic cures.  But I am also fairly sure you are looking at real long term expense in either money or labor to achieve the goal.  Suggest trying in very limited areas.

The hard lesson to come out of fighting with this soil for decades has been build organic to buffer pH and grow what grows.  If it needs a different soil type like well drained sand don't fight the soil but simply go raised bed and get above the soil.  And for soil pH give up.  The amount of chemicals I have thrown at the soil thru the years is huge.  Yet even in areas where I really tried I will guess measuring soil pH you can't hardly tell I even tried a decade later.

My little story...

Once upon a time about 3 years ago, A pine sprouted in my yard. Due to one thing and another, I didn't remove it. Last year, when scouting my backyard for a location to plant blueberries, I spied this 8 foot tall wonder, and plopped the blueberries down around it. I thought it was awesome to have an area that was already a touch more acidic.

Redhawk, you have bust my bubble.

When I apply one of the above treatments to this rough guild area, is the tree likely to hang on to the acidity? As an alternative, I could cut down the existing tree, so it does not hold on to the current PH. I likely could transplant another volunteer in this place after several acidic treatments over summer, fall, winter. Does this sound like it would work?

Yes Joylynn, the pine will hold onto the acidity you introduce. Studies have shown that pinus are great for that, they will (through their pine needles and other detritus falling to the ground)buffer that acidity to hang onto it in the soil.

Redhawk

Excellent info.

I am curious if anyone has taken the different bits of conifers and tested the pH.   I have some vague memory of this and the needles turn out to not be a low pH.   Some of the duff is, but the rest is not.  

Further, there is an element of the area the conifer is growing in.   My understanding is that the same species will grow four to seven times faster in a warm climate.   So here in Montana, it will take 80 years to achieve the mass of the same species in, say, florida.   So trees that are 30 years old and lowering pH by 0.2 ...  well, those trees are still teenagers.  

So if we are in an area where a lot of the soils are 7.5, and there is an area that has been a conifer forest for more than a hundred years where the pH is below 6, I think that lines up well with what is presented.  And rather than the school of thought that the tree duff causes the acidity, the school of thought I have been preferring in the last eight years or so is that conifers are "calcium pigs" - and taking the calcium out of the soil lowers the pH.  So when you say

Acidification also occurs when base cations such as calcium, magnesium, potassium and sodium are leached from the soil.  

Then I'm thinking that it makes sense that the conifer may be pigging up more than calcium.

Really huge trees will consume far, far more than little trees.  I really like the blueberry tie-in.  That is a really tough nut to crack and a lot of people ask about it.   I have suggested the conifer tie-in before, but now I can see the need to amend my thoughts with "young conifers won't do enough."

For ten years I have wanted to see some reports on the pH of different types of conifer duff.   Is there anything like that available now?  

I haven't found any studies on conifer duff as far as the actual pH of the duff.

I do know that if you want to use conifer duff for the purpose of acidification it is the cambium layer with the resin phylum that you really want to be using.
I did a few tests way back in the 60's of several California species of pines and found that it is the bark and cambium layers that contain the most acidity when compared to leaves or the wood the bark is about 40% more acidic with the cambium but only 15% more acidic without the cambium.

This is something that would be interesting to do further study on in the future (for me).

C. Letellier wrote:

 I have killed many hundreds of trees over decades learning that lesson.  Since my soil is clay, high salt and high pH the choices are very limited.(PS I am US grow zone 4 borderline zone 3)  So far I have 3 evergreens that are making it in my ground.  Austrian pine works, Colorado Blue spruce works and a couple of varieties of juniper.  Now supposedly white pine, eastern red cedar and lodge pole are supposed to work too but I have killed all of them on a regular basis.  Eastern Red cedar I am told is dying from salt damage.  

My pH is slightly better (8.5-7.5 depending on organic material) but not much (Lakeview Water District on the South Fork west of Cody) and I'm planing on adding trees.  What varieties of juniper have been working for you?  Have you had any luck with black locust, honey locust, or Osage Orange?

Bryant RedHawk wrote:
I do know that if you want to use conifer duff for the purpose of acidification it is the cambium layer with the resin phylum that you really want to be using.
I did a few tests way back in the 60's of several California species of pines and found that it is the bark and cambium layers that contain the most acidity when compared to leaves or the wood the bark is about 40% more acidic with the cambium but only 15% more acidic without the cambium.

Would soaking wood or wood chips in a barrel of water make the water a bit more acidic for irrigation?  Being a desert dweller, I have very alkaline soil and water.

hau Juanita, It should be better to use the bark than to use the actual wood for this purpose. (Citrus fruit peels also are pretty good for making an acidic water)