Do we need to pH adjust our nutrient solutions?

[Elvin]

I think the alkalinity of the tap water is a factor here. That may be why we're seeing such a range of results.
I've seen people on this forum, who's opinion's I highly respect, get a different result. So there is some variable going on.
HP Pro-Mix is said to be buffered, dolomite I think, but I wonder to what strength, in comparison to good 'ole topsoil.
For me, 5.8 feeds are working wonders. I think I will be staying with MC as it is simple and effective. Plus, a little bag goes a looong way! I'm tempted to throw some random pH tap water at my girls to see, but I'm now at the 50% mark in flowering.
I've got enough to worry about trying to avoid budrot, and cal/mag issues. and taming the "stretch" monster.
I have to give MC credit, I have had no issues after I started pH ing these girls feed. Would I like to skip that step? I sure would. However, it is a small price to pay to avoid the "Let's have a shit show in the garden" episode.
For folks in the "Iowa topsoil", I would think the buffers could be much better/stronger/diverse.
Ps: I may have to try MC on the tomatoes... fighting a little bud rot on some of those, and they were planted in containers with good ole potting soil! LOL

I'm using well water that tastes great but is a little hard with calcium (towels dry a little stiff on the line) and of course there is good 'ol natural magnesium in it as well. I got tired of paying $70 a month for water when I had my own well. Rural water around here is very good, in fact it is considered "soft" because the ppm is so low but I'm not paying $70 for it.
Kelp's stuff is similar to MC (smells the same) but is a little more broken down (2-3 parts for each part of the flowering cycle ending with 0% N with the last feeding cycle in flower) to make specific nute adjustment easier.
As to my tomatoes, I had them in 2-gallon containers that could not support the plant with one watering per day. I cut the bottoms off the pots and sat them on top of last crop's grow bags (they had a previous crop grown in them so it was time for new soil) that were 7-8 gallons. The roots are now into that but I had to resort to a water drip to keep it from wilting in the heat (the roots just need constant water) I just toss a spoonful of MC on them every so often and those round balls dissolve in a few hours of sitting on the soil. I've got some old Fox Farm nutes and those will be what I use when the MC is gone. Won't work as well but it is just tomatoes.
Dollar Tree tomato seeds from last year and they are getting big from the MC.

 

[Elvin]

HP Promix is buffered with Dolomite? That must be some bad @$$ mixture . . .

 

[Rad Man]

HP Promix is buffered with Dolomite? That must be some bad @$$ mixture . . .

I have got to watch this movie!!!

 

[Amy Gardner]

Promix is buffered primarily with calcitic limestone, not dolomite. It only has a small amount of dolomite in it.

here is pthorticulture on calcification lime vs dolomite lime

Calcitic vs Dolomitic Limestone in Growing Media | PRO-MIX Greenhouse Growing

www.pthorticulture.com

 

[Rad Man]

Promix is buffered primarily with calcitic limestone, not dolomite. It only has a small amount of dolomite in it.

here is pthorticulture on calcification lime vs dolomite lime

Calcitic vs Dolomitic Limestone in Growing Media | PRO-MIX Greenhouse Growing

www.pthorticulture.com

Thank you for that article, it was quite good. It stated alkalinity in the water was a factor. I'm guessing that's why we are witnessing varying results among the forum. I've never measured the alkalinity of my tap water, but the map posted earlier by Felipe, in "Shed's thread, says I'm at the far end of the scale.

 

[MightyMoe22]

. So your pH pen can collect dust until you decide to slurry test your soil. Then you can brush it off!

How does one slurry test their soil correctly?

 

[InTheShed]

To do a slurry test, you take soil from about halfway down (I go down the outside of the pot so as not to tear up old roots) and add an equivalent amount of distilled water as grams of soil (10 grams of soil, add 10ml water). If that doesn't make a slurry, use 20ml (or enough to make a stirrable slurry).

Stir it up, wait 15 minutes, stir again. Do that for at least an hour, longer is better, and then put your calibrated pH stick in the water. That's the pH of your medium.

 

[bruno12345]

So nice this topic is here. Ive ran two entire grows, without having to address pH. Peat+vermiculite+EWC.
but my water, and water + nutes is very low into alkalinity.

Also found an article of a University teacher, cant remember now, saying that Cannabis is a plant that can thrive in a large pH scale. going from 5.5 to 7.0 without leaf deficiencies.
Which give us a larger field to operate our medium pH's. altough a 5.5 to 6.5 should be considered for addressing errors in time.

Just wanted to add, i saw in the early pages, the discussion being that, to acidify the Mix, one should invest in ammoniacal nitrogen, and other ions capable of exchanging an H+ at root level.
And that pH of the liquid solution wouldn't matter. And it is not completely true.

The source of the nitrogen can correct minor imbalances. And it takes around 2 weeks for the full effects.

As a tool for medium imbalances in high ph problems, a very low pH soil drench could bring the pH of the medium down.
Example: Soil drench with pH 4.0, producing leachate. Process can be repeated. takes around 5 days for full effects.
Can be repeated.

Huge pH imbalance, very High pH, other ways didnt solved it -> iron drenches.

 

[InTheShed]

So nice this topic is here.

Thanks bruno! I thought it was good to get the science out there.

Also found an article of a University teacher, cant remember now, saying that Cannabis is a plant that can thrive in a large pH scale. going from 5.5 to 7.0 without leaf deficiencies.

I'd like to see that if you don't mind posting a link. Cannabis will grow in a medium with the correct pH for that medium.

Which give us a larger field to operate our medium pH's. altough a 5.5 to 6.5 should be considered for addressing errors in time.

The pH of the growing medium is key. I don't advise growing in soil with a pH of 5.5 or peat with a pH of 6.5.

The source of the nitrogen can correct minor imbalances. And it takes around 2 weeks for the full effects.

Not sure what you consider minor, but I have brought the pH of ProMix HP down from 7.4 to 5.8 in two weeks using nutrients that are 33% ammoniacal and 67% nitrate nitrogen.

Much safer than bathing roots using highly acidic or base dunks. The savings of a week doesn't seem worth the risk to me. And what are you feeding your plants while you do that, since most nutrients are not designed to be dissolved at the extremes of pH?

 

[bruno12345]

Thanks bruno! I thought it was good to get the science out there.

I'd like to see that if you don't mind posting a link. Cannabis will grow in a medium with the correct pH for that medium.

The pH of the growing medium is key. I don't advise growing in soil with a pH of 5.5 or peat with a pH of 6.5.

Not sure what you consider minor, but I have brought the pH of ProMix HP down from 7.4 to 5.8 in two weeks using nutrients that are 33% ammoniacal and 67% nitrate nitrogen.

Much safer than bathing roots using highly acidic or base dunks. The savings of a week doesn't seem worth the risk to me. And what are you feeding your plants while you do that, since most nutrients are not designed to be dissolved at the extremes of pH?

Thanks for asking it, took a read in the pH matter, but not only it, has plenty of good info.

You can gain access by googling "Nutrient Matters Cannabis", its from NCSU, in the beginning has a pH session.

I think the confusion here is between optimum pH, and leaf deficiency, and also because i was talkin about the peat mix i use.

i do not intend to say that a medium with a ph of 7, even (or specially?) in soiless, is something to achieve.
Its a high limit number, from wich deficiencies from high ph seems to appear.

We surely would want our pHs right when choosing a medium, and to take action before achieving maximum/minimum limits, or deficiencies itself, because the harder you go up, the harder will be to drop down.
Monitoring and anticipation.

Its also not a "strictly scientific article", but a sample created by the professor and students along a lot of growing houses and an observation. from the diversity of marijuana, we may have different values.

Its also nice to see your report, cause i had seem science articles on other crops, with 100% ammoniacal nitrogen and no effect in soil pH.

The acid dunk is for non responsive to ammonium nitrogen correction, from the NCSU mannual.
If your plant is drifting on high ph issues, an acid dunk with posterior crop care could actually make your nutrients work.

 

[InTheShed]

Some conflicting statements in there, like:

A recommended substrate pH of 6.0 to 6.5 often is cited as the standard. However, we have observed pH ranges between 4.0 and 5.0 or greater than 7.0 during our visits to commercial greenhouses growing cannabis.

and then

When adapting these values to a monitoring system, the recommended pH zone to target would be 5.8 to 6.2.

Source

Something to keep in mind when reading research done by many ag departments is they are often done in large planting areas like fields or commercial greenhouses. There is a difference between what applies there and what applies to the container grows most of us are doing. Finding ones that talk about container growing will give you more applicable growing advice.

 

[bruno12345]

When adapting these values to a monitoring system, the recommended pH zone to target would be 5.8 to 6.2.

Like i said.
one would not advise to seek pH 7 in the growing medium. But one knows pH 7.0 probably wont give visual deficiencies to most of cannabis plants.
Altough, when monitoring your pH, you should aim for more "middle values", so you dont act only when a deficiency is there, or near deficiency.

Not conflicting.

And also, data from commercial growers are surely welcome, as they have sometimes hundreds of plants. pH analysis of soil or soiless, and then visual deficiencies acessing doesnt change the fact that this is being done on a medical cannabis plant.

 

[Diatomacious]

Makes sense if you think about it since the alkalinity of the water will not greatly affect the pH of the soil. Pro-mix contains lime in order to raise the pH of the peat moss from around a 4.0 up to the 6.0 you need to grow in. It takes a lot more lime to raise the pH of the soil than it would to raise the pH of the nutrient solution so the solution has negligible effect on the soil.

In coco coir or rockwool you will have to pH since there is no lime buffer present in the soil to negate the effects of the pH of the nutrient solution.

 

[chikkit]

Below is info readily available at the Promix website for anyone to view.

What Changes Growing Medium pH?
Contrary to popular belief, the pH of the water does not influence the pH of the growing medium. Actually, it is the bicarbonate and carbonate levels in the water, known collectively as alkalinity, the potential acidity or basicity of the fertilizer and the plant itself:

Water Alkalinity
As stated above, water alkalinity is a measurement of carbonates and/or bicarbonates in the water, or another way to put it, is the amount of limestone dissolved in the irrigation water. The higher the alkalinity, the faster the pH of the growing medium climbs regardless of the water pH . If water is passed through a reverse osmosis unit, then alkalinity is very low, so the water does not cause the pH of the growing to rise quickly. Reverse osmosis units are not necessary for most water sources if the fertilizer is properly matched to the water profile and the crop grown.

Fertilizer
Quality water soluble fertilizers typically have the potential acidity or potential basicity posted on their labels to predict their influence on the pH of soilless growing medium. For example, the higher the potential acidity of the fertilizer, the more acid it is. This is often determined by the ratio of nitrogen forms. Ammonium and urea are acidic forms of nitrogen which cause growing medium pH to drop and nitrate is basic which causes growing medium pH to rise. Therefore, if your water has high alkalinity, a fertilizer that has a higher ratio of ammonium to nitrate can be used to minimize pH climb in a growing medium. Also, as a rule, most calcium-based fertilizers are alkaline and cause the pH of the growing medium to increase even if the water goes through a reverse osmosis unit.

It may help in clearing some things up.

I’ve read this whole thread and will try to rein in my questions. Just wanted ask though. I have hard water, alkalinity of 155, ph varies between 8-10. Growing in Pro-mix HP. I’ve had issues with nutrient lockout when the ph tester wasn’t working properly, plants seemed to recover when using PH Down properly but still not to happy with how the plant growth overall. Using GH flora grow series. Is that the best nutrient system to use? It’s lower in ammoniacal nitrogen and higher in nitrate nitrogen. (Incidentally our tap water is already high in nitrates.). I’m wondering if I should be looking for ferts that have a higher ammoniacal nitrogen and lower nitrate one.

 

[InTheShed]

One thing to keep in mind if your water has pH that high is that your nutes may not dissolve completely. Some elements might not be finding their way to the plant because of that.

With a starting pH that alkaline I would add the pH down first to get into a range that works with your nutes line, and then add your nutes.

At that point you don't need to re-pH as the ProMix will handle it from there.

 

[Diatomacious]

With a starting pH that alkaline I would add the pH down first to get into a range that works with your nutes line, and then add your nutes.

Most nutrient will cause a drop in pH due to the nature of the chemicals used to make them. This should bring your water down to at least a 6. That is very sweet water if not and you may want to consider RO.

 

[InTheShed]

Most nutrient will cause a drop in pH due to the nature of the chemicals used to make them. This should bring your water down to at least a 6. That is very sweet water if not and you may want to consider RO.

If the pH is that high I wouldn't rely on the nutes themselves to lower the pH.

See what range the nute manufacturer recommends for their line.

 

[Diatomacious]

Growing in Pro-mix HP.

That pro-mix should buffer it no problem (peat starts off with a pH of around 3.5-4 and must be limed to bring it up towards the 6 range). Probably don't even need to check but I always set to a 6 just in case so it doesn't have far to go.

 

[MrSauga]

I’ve read this whole thread and will try to rein in my questions. Just wanted ask though. I have hard water, alkalinity of 155, ph varies between 8-10. Growing in Pro-mix HP. I’ve had issues with nutrient lockout when the ph tester wasn’t working properly, plants seemed to recover when using PH Down properly but still not to happy with how the plant growth overall. Using GH flora grow series. Is that the best nutrient system to use? It’s lower in ammoniacal nitrogen and higher in nitrate nitrogen. (Incidentally our tap water is already high in nitrates.). I’m wondering if I should be looking for ferts that have a higher ammoniacal nitrogen and lower nitrate one.

Ideally you'd like to have your NO3-N in around 70-80%. If you find you are outside of that, then yes I would look at trying a different nute line.

 

[Diatomacious]

If the pH is that high I wouldn't rely on the nutes themselves to lower the pH.

pH down is just more chemicals... GH uses phosphoric acid (H3PO4)... if it still ain't to 6 by the time you add your nutes though.

Ideally you'd like to have your NO3-N in around 70-80%. If you find you are outside of that, then yes I would look at trying a different nute line.

I don't notice much difference between NH4 and NO3 nitrogen or even Urea for that matter. I still like to include at least a couple sources and not put all my eggs in one basket.