Ask a Question forum: PH question

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Berkshire county Ma
Feb 17, 2018 11:48 AM CST
In gardening applications you have 2 basic scenarios...soil and water in a pot or in a garden bed. Plants rely on an exact ph,..different numbers for different species. But the correct PH basically allows uptake of nutrients for the plant. If the number is way off the plant wont grow to its full potential or in some cases not grow well at all due to nutrient deficiency. If you want the best tasting tomato you want maximum uptake so its packed with flavor.

The problem with Garden beds is that they are at the mercy of rainwater. The problem with water from the house is that its ph may be no where near where you want it. So you need to adjust it with PH up or Ph down solution or you can amend soil with various buffer products which are inherently acidic or alkaline to adjust it. Limestone pebbles, peat moss, perlite, magnesium sulfate etc etc. This is called amended soil...a sort of recipe of things.

Theory (sort of fact from my experience)
So if you had neutral PH water...say distilled water with a neutral PH and poured it through a pot of amended soil, the run off at the bottom would have a number..... maybe 6.5. But if you have a rainfall of 7.5 Ph water mixed with the 6.5ph inherent to that pot of soil,.. then you get some in between number I would guess, say 7.0 (?)..... But in this tomato scenario you want like a 6.2 .. T The common garden is out in the open and will have the rainwater introduced at random,.
I guess the question you think that the end PH number flowing out the bottom of the pot is the divisible of all factors that influence PH? Water and soil
Name: Baja
Baja California (Zone 11b)
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Feb 17, 2018 12:45 PM CST
I adjust the pH of the water I use for watering potted plants to just below neutral (pH 6) and never concern myself with the pH of the water flowing out the bottom. Plant roots generally function over a limited range, not a specific point. I would not be concerned about the pH of rain water, which seems to be pretty magical stuff compared to our hard well water (even after it has been adjusted). If you want to fix the pH going in, you can try to buffer it (there is a product called Acid Buffer that I use which has this property of resisting pH change after it's been adjusted). These concerns only apply to potted plants. I never adjust the pH of water that goes to plants in the ground.
[Last edited by Baja_Costero - Feb 17, 2018 1:34 PM (+)]
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Minnesota (Zone 3b)
Feb 17, 2018 12:49 PM CST
With rare exceptions, at least in North America, plants can survive in certain PH ranges, not exact numbers.
I have acidic soil and did have acidic city water for decades, in my South garden and that has not stopped me from growing anything except Blueberries which are one of the ones that are more fussy as it is not that acidic.

Rain also has Nitrogen which is why it makes lawns look better after a dry spell than any irrigation systems in existence unless you are using fertilizer.
Name: Will Creed
Professional indoor plant consultan
Feb 17, 2018 1:53 PM CST
It is the pH of the soil in the root zone that matters. Presumably, the pH of the runoff would be the same. But why not just test the pH of the soil?
Will Creed
Horticultural Help, NYC
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Berkshire county Ma
Feb 17, 2018 4:56 PM CST
Yes so the combined result of mixing the PH of the rainwater with the amended soil mixture. This question is about control. I understand there are ranges...but if your experimenting and want to find what a certain Ph range in specific will do then you need exact data. At the very least I wanted to know if the water PH and soil PH always balance to a middle number .

Basically id have to stick to an exact soil recipe i expect would off set the rain water ...the rain water PH taken from a previous rainfall and then measure the PH runoff out the bottom of the pot and that would give me the PH of that mixture.
Name: Baja
Baja California (Zone 11b)
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Feb 17, 2018 5:25 PM CST
I don't think rain water is particularly well buffered, which makes it relatively easy to change the pH to whatever you want it to be. Especially compared to well water. It will generally be slightly acidic due to the CO2 it picks up from the atmosphere on the way down. It will be more acidic (so-called acid rain) if you live near a power plant or something and nitrates and sulfates get involved. That sort of thing would apply in the upper Midwest (for example) where there is vastly more nitrogen entering the rainwater as it falls than in say Oregon.

But I doubt the pH would change dramatically from one day to the next, such that actually measuring it regularly would do you any good. If you want to fix the pH of your output water, fix the pH of your input water with a buffer that resists change. (See above.)
[Last edited by Baja_Costero - Feb 17, 2018 5:36 PM (+)]
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Name: Frank Mosher
Nova Scotia, Canada (Zone 6a)
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Feb 17, 2018 6:41 PM CST
If I ever get to the point that I feel it is necessary to adjust the pH of individual plants, it is time to "put me down!" Understanding that certain plants prefer low pH, i.e. Blueberries, Hydrangea, Azaleas, Rhodos, etc., to go any further except for a couple of veggies, is taking gardening a little too seriously in my opinion. I have a couple of old "well test" holes on the property, in the woods. I have tried to have goldfish and koi in same, but every time there is a heavy rain, the fish die, because of the "neutral" pH of the rainwater entering the highly acid water of the ponds. The pH shock is a killer, consistently. Pity. I tried adding a little lime to the ponds, but doesn't address the issue.
Name: Rick R.
Minneapolis, MN, USA zone 4
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Feb 18, 2018 9:57 AM CST
Oh if only there were an answer set in concrete, but it is very complex. Pure water (H₂O) is not buffered, while all soils (with quite a large range of capacity) are. Acids in soils tend to be more water soluble in soils than bases.

You are right that the pH of added water (like rain) and the pH of the soil react with each other, and the resultant pH in the soil is somewhere in between. About in the middle? No. About 75% of the water pH? No. About 75% of the soil pH? No. The pH of added water has comparatively minuscule effect on soil. (This, taking into account comparative volumes. Constant watering over time may significantly change soil pH.) Remember too, that pH measures in a logarithmic scale, where each integer represents ten times the acidity (or alkalinity) of the next.

So while exact measurements are always wanted, what do they actually reveal, and is an exact interpretation necessary? Rarely. Stay in the ballpark, and try to work with mother nature, rather than against it.
Berkshire county Ma
Feb 18, 2018 2:31 PM CST
Leftwood your correct.... You must have a background in chem. This is what I learned. I wonder why PH changes over time...nutrient depletion or dillution of the elements?
from a artical i found - " Recently, some growers have expressed concern about the "high pH" of their irrigation water and its potential adverse effects on plants. The purpose of this article is to allay some of these concerns by pointing out the difference between "high pH" and "high alkalinity".

Alkalinity and pH are two important factors in determining the suitability of water for irrigating plants. pH is a measure of the concentration of hydrogen ions (H+) in water or other liquids. In general, water for irrigation should have a pH b etween 5.0 and 7.0. Water with pH below 7.0 is termed "acidic" and water with pH above 7.0 is termed "basic"; pH 7.0 is "neutral". Sometimes the term "alkaline" is used instead of "basic" and often "alkaline" is confused with "alkalinity". Alkalinity is a measure of the water's ability to neutralize acidity. An alkalinity test measures the level of bicarbonates, carbonates, and hydroxides in water and test results are generally expressed as "ppm of calcium carbonate (CaCO3)". The desirable range f or irrigation water is 0 to 100 ppm calcium carbonate. Levels between 30 and 60 ppm are considered optimum for most plants.

Irrigation water tests should always include both pH and alkalinity tests. A pH test by itself is not an indication of alkalinity. Water with high alkalinity (i.e., high levels of bicarbonates or carbonates) always has a pH value ÷7 or above, but water with high pH doesn't always have high alkalinity. This is important because high alkalinity exerts the most significant effects on growing medium fertility and plant nutrition.

High pH and High Alkalinity Effects on Plant Nutrition
Potential adverse effects. In most cases irrigating with water having a "high pH" ( 7) causes no problems as long as the alkalinity is low. This water will probably have little effect on growing medium pH because it has little ability to neutralize acidity. This situation is typical for many growers using municipal water in Massachusetts, including water originating from the Quabbin Reservoir.

Of greater concern is the case where water having both high pH and high alkalinity is used for irrigation. In Massachusetts this situation is most common in Berkshire county. One result is that the pH of the growing medium may increase signifi cantly with time. This increase may be so large that normal lime rates must be reduced by as much as 50%. In effect the water acts as a dilute solution of limestone! The problem is most serious when plants are grown in small containers because small volum es of soil are poorly buffered to pH change. Therefore, the combination of high pH and high alkalinity is of particular concern in plug seedling trays. Trace element deficiencies and imbalances of calcium (Ca) and magnesium (Mg) can result from irrigating with high alkalinity water.

It is much more difficult to predict the effects of irrigating outdoor flower crops, gardens, and landscape plants with water having high pH and high alkalinity. On the one hand, in some parts of the United States, long-term irrigation of crops with wa ter high in bicarbonates and carbonates has led to yield-limiting trace element deficiencies which must be corrected with special fertilizers. On the other hand, in New England, several factors probably act together to partially offset the effects of high alkalinity water. First, rainfall levels are relatively high and historically this has caused Ca and Mg ions to leach from the soil. These are replaced with H+ and the result is acidic soil. Second, this acidification may be helped along by the rather ac idic rainfall common in this region in more recent times. Third, acid-forming fertilizers also help counteract high pH and alkalinity."

Im in Berkshire county MA... My land is largely limestone ledge,.the recent ph reading I took from rainfall was 7.5 and the local water was near 7. Im not sure what my well water will be because i haveant drilled it yet. Its a property in progress.

I also learned that PH is a measure of acidity basically...strong r weak and not a measurement of alkalinity. Alkalinity is measured in PPM with another meter.

I mention all this because im working with what seems like a low acidity of rain fall and soil..though as Leftwood says the alkalinity of water such as rainfall wont have much effect if its alkaline conent is low. I need to get a meter. Basically I think a peat heavy soil will counter the high ph lean im working with.

Im working on this because i believe getting the nutrients and ph correct will result in a better end product.

Name: Carol
Santa Ana, ca
Sunset zone 22, USDA zone 10 A.
Charter ATP Member Hummingbirder Lover of wildlife (Black bear badge) Orchids Region: California Plant Identifier
Feb 18, 2018 4:24 PM CST
Thank you for the article. It clears up a lot of wrong assumptions. I don't know what I can do about it, as I'm in So.Cal, where we have no rain to speak of , and most of our water comes from 700 mi. north of here, but it's still good to know these things.
Name: Baja
Baja California (Zone 11b)
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Feb 18, 2018 6:39 PM CST
Original source here

The question of alkalinity is moot with rain water to the extent it normally does not have enough dissolved solutes to actually generate alkalinity. It matters with well water which generally has much more dissolved carbonate and can require quite a bit of acid to be brought into the neutral range (see above). You are not going to get any useful information from measuring the alkalinity of rain water, normally (and not just because it normally is not alkaline). You also do not really need a second meter for alkalinity if you can measure the amount of acid needed to neutralize the pH of a given water source.

There is another measurement system which you can use to conveniently compare the carbonate hardness of groundwater. You can buy a kit to measure carbonate hardness using indicator drops and the answer will relate directly to alkalinity below pH 8.5. Again, this is not something you would normally find useful when applied to rain water, but it can come in handy with well water or if your public water supply comes from groundwater (like ours does).

You should be aware that a rain water pH of 7.5 is unusually high and would tend to indicate there is something unusual in the air, literally, for example from dust blown off the land. Maybe check how you are measuring pH and calibrate with known standards. In the absence of lots of particulates in the air it should be below neutral, usually below 6, especially in your part of the country.

To explain why carbonate is what you would measure to approximate alkalinity, it's important to recognize the sources of acidity in rainwater and alkalinity in ground water, respectively. Rain picks up CO2 from the atmosphere on its way down and this converts to carbonic acid in rain water, which lowers the pH to around 6 or so. On the other hand, groundwater picks up dissolved carbonate from limestone and other sources, which raises pH and alkalinity.

These are opposite ends of a common spectrum. When you add acid to alkaline well water, you convert that dissolved carbonate (the dominant buffer maintaining its high pH) into dissolved bicarbonate and eventually carbonic acid. So you would measure dissolved carbonate because that tells you roughly how much acid would be required to return the pH to near neutral.
[Last edited by Baja_Costero - Feb 18, 2018 8:03 PM (+)]
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Berkshire county Ma
Feb 19, 2018 11:14 AM CST
Thank You baja. Thanks for the articals and the input. I assume once the well is drilled they will test the water and give me a full report anyway. So I will know whats up. Regarding the rainwater and its influence...I scooped up some snow from a recent storm, melted it and measured the PH with my meter. Its possible that other elements were possibly mixed in which raised the PH. I really should set a bucket out and try that.

Will save this info. Thanks again everyone

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