Raising or Lowering the pH in the Soil Mix

by Dowzer

Growing in soil and adjusting pH levels

A lot of gardeners have trouble with the pH of their soil. A high pH can lock out needed nutrients and mimic other problems like Fe and Mg deficiencies. The biggest mistake new growers make is to try and correct pH problems too quickly. The first step in determining if high pH is the real problem, is to pick up a good pH tester. Don’t be afraid to shell out the cash for a good one, it’s well worth it!

Here are some recommendations: (All sell for under $100.00)

Milwaukee makes two styles of hand-held pH meters. A small “pen” called the Sharp and the larger Smart Meter. Both are easy to use. The Sharp pens are splash-proof (although not totally waterproof), and have a large easy to read display. They also have a detachable, replaceable probe.

Oakton – Same type of pH tester as Milwaukee makes, but it’s made a little better imho. These are totally waterproof. (It floats.)

Shindengen ISFET pH Meters are state-of-the-art pH pens and work with a totally different method of measurement. This pen uses a solid state Ion Sensitive Field Effect Transistor (ISFET) instead of the fragile glass electrodes used by traditional pH pens. They have replaceable tips that change from opaque to clear when they need to be changed.

What is pH, and what do the terms acidic and alkaline mean?

The acidity or alkalinity of the soil is measured by pH (potential Hydrogen ions). Basically it’s a measure of the amount of lime (calcium) contained in your soil, and the type of soil that you have. A soil with a pH lower than 7.0 is an acidic soil and one with a pH higher than 7.0 is considered to be alkaline. A pH of 7.0 is neutral.

Adjusting your soil pH :

Once you have determined the pH of your soil with a good tester, you can amend the soil if needed to accommodate the plants in your garden using inexpensive materials commonly available at your local garden center.

Adjust soil pH slowly over several days time, and check pH often as you go. Radical changes in pH may cause osmotic shock damage to the roots.

Raising soil pH : (to make it more alkaline)

It is generally easier to make soil mixes more alkaline than it is to make them more acidic. The addition of dolomite lime, hardwood ash, bone meal, crushed marble, or crushed oyster shells will help to raise the soil pH.

In soil: add dolomite limestone to the soil; use small amounts of hydrated lime.

Raising hydroponic pH : (to make it more alkaline)

In hydroponics: use potassium silicate, provides silicon at an effective doseage. In bioponics/hydro-organics: add small amounts of sodium bicarbonate or lime.

Lowering soil pH : (to make it more acidic)

If your soil needs to be more acidic, sawdust, composted leaves, wood chips, cottonseed meal, leaf mold and especially peat moss, will lower the soil pH.

bloodmeal/cottonseed meal during vegetative; bonemeal during flowering.

Lowering hydroponic pH : (to make it more acidic)

In hydroponics: use nitric acid during vegetative; phosphoric acid during flowering.

Stabilizing pH with Dolomite lime

The best way to stable PH is by adding 1 ounce of Dolomite Lime per 1 gallon of planting soil.

Dolomite Lime is available in garden nurseries. Buy the fine Dolomite powder (There may be several kinds of Dolomite like Rough, Medium, Fine)

Dolomite Lime has been a useful PH stabilizer for years, since it has a neutral PH of 7 when added to your soil it stabilizes your soil at PH 7.

Mix the dry soil medium and dolomite together really well, give the mix a good watering then after the water has had chance to settle and leech into the soil a bit give the mix a really good stir. Then water the soil/lime mix and give it another stir

Best plan is to mix fine dolomite lime into your mix before planting. Fine Dolomite will help stabilize your pH; however, if the ph becomes unstable or changes, you can then use Hydrated Dolomite Lime. Add some of the hydrated lime to luke warm water and give it a good stir then water your plants with it. Give the plants a good watering with this hydrated lime added and your PH should fall or rise back to 7

Dolomite lime is also high in two secondary nutes that can often be overlooked by fertilizers; dolomite is high in both (Mg) Magnesium and (Ca) Calcium.

16 comments to Raising or Lowering the pH in the Soil Mix

  • Jon not apple seed

    I think the name calling is pointless. Isn’t this a forum for people to get help rather than made fun of for asking?

  • CalBear

    Remember we are dealing with a WEED! Most of us old timers started growing in the back yard, with only fish emulsion added once or twice during entire season. Now, Hydroponics and Fox Farms have complicated and confused what used to be so simple. Here are some back to basics tips: 1. Use less water, period. 2. If your car shows spots, add Apple Cider vinegar to your water, 1 tsp./gal. every other day, re-check pH. 3. If you live in a rainy climate, your soil will be acidic. Arid? Alkaline. 4. If your pH is less than 7, but greater than 5, go watch T.V.

    PS: Best nutrients? all Earth Juice products, about 1 cap full per gallon, plus molasses, about twice a week. Use only growth for Veg, Blooms for flower, of course.

  • Anonymous

    I never had a problem until i added dolomite lime to my mix this year. Now have older leaves starting with necrotic spots until they die off. Wont use it again

  • steve

    My plants were doing great at 2 months into veg and now that I’m about to put them into flowering my PH run off is at 4….. I’m in soil and looking for suggestions…

  • Anonymous

    Ok, I’ve been experiencing lockout, extreme clorosis, and all kinds of crap that I never experienced until I started listening to advice, reading books, posts, etc. I think dolomite lime is my problem. In my case, my default water is high in lime, calcium, and probably mg as well. My default ppm is around 220-250, ph is around 7.0. I forget what my ec is off hand,but its short of double the ppm #. Using RO water isn’t an easy option here, but I believe it would help at 1/2, or 3/4 strength. I have two high end ph/ec/ppm meters. I water at 6.2-6.5. My runnoff continues to stay high, like 7.5ish :-0 A ph soil probe will say my soil less mix is around 7.0. I will skip the dolomite next time. I will post what happens.

    Another weird thing that happens with my defualt water is… It comes from the well at 7.0ish. Airstone the water for a day and it will raise the ph to the 8.1+ range. I understand some of the concept of how that happens, but that can throw someone off too. I no longer Airstone my water. I’m gonna get to the bottom of this crap!

    • Anonymous

      A couple more details… My soilless mix is sphagnum and peralite (which should be wanting to run a lower ph by default). Both my meters are Hannah, and calibrated at 7.0, and 4.0. I feed with Advanced ph perfect.

      I am going to get my default water tested. You cannot wash a vehicle with it. It will leave white spots all over the place. It will do the same to a water reservoir. All of the well water where I’m at comes from a vast limestone aquafir. It tastes, and smells good, but its definatly high in calcium carbinate at minimum. Most of the well water tests out nearly the same everywhere in my area. I swear using dolomite lime in my containers is what’s causing all my new problems.

      • Anonymous

        I got rid of the dolomite lime, and things are going much better. I also changed my water. I used RO water @ about 90%, and 10% well water. My default ppm is now 45. I don’t understand why people recommend dolomite lime to everyone. It has it’s place and purpose, no doubt about that. Theres a such thing as to much calcium, and mg too. I think in the past I could get away with what I used to do buy luck. Luck as in, my root zone was in range 6.0-6.3 ish. Water that was high in calcium carbonate, combined with spagnum peat… Seems the calcium carbonate was keeping me in range. IOW.. Not letting my spagnum drop into the PH 5 range. Then I added dolomite lime 🙁 That threw my “luck” in a downward spiral. My symptoms in my last grow looked like I was deficant in about 5 things. Iron, P, K, MN, MG, and so on. In many ways, it didnt look like it wss getting enough nutes as well 🙁 What a disaster! In reality, I think it was mainly to much calcium, and the inability to get my ph low enough. Thank you dolomite lime !! 🙁 Using quality nutrients that have both mg, and cal is a much better idea. At least that can be flushed out.

        • Anonymous

          Let’s keep this short… You have to have a buffer of some sort when working with spagnum, let alone ferts w low pH. To much dolomite during flowering will cause problems. Hitting the sweet spot ammount is what one is looking to do. Sway to far left, or right and you will have problems. Figuring out what works best with a given set of envirmentals, and materials is what one is looking to do. Not copy what someone else is doing, as their situation is likely somewhat different. I wouldn’t recommend anyone not use dolomite lime in their set up. But I wouldn’t recommend an ammount either. To many variables. No more to say about this.

  • Samu

    ; situate acid’ lonivg plants in the lighter native acidic soils and introduce less acidic lonivg flora for the dryer climes.In the end lime is applied to enable the native soils to more readily give up or share their contribution of nutrients thereby extending the ability to serve the native plant populations. By generally encouraging the soil to enable an approach to optimum for a particular plant population native or introduced, not always a neutral state of ph7 is desirable but ultimately be balance to serve one’s planting plan.In all case a ph test will provide a perspective necessary for feeding your garden.Donald M

  • Keith

    I’ve heard foxfarm has to be adjusted in most cases

  • Anonymous

    If you have Dolomite lime in the mix you need to feed at about 5.5. Ocean forest 6.3 Dolomite lime is so dumbass in containers. So dumbass! Nothing likes 7 and getting it to balance at 6.2 is way harder than just giving it 6.2 and causes issues. When 0.1 adjustments high or low make a significant difference, Dolomite lime is for idiots.

    • doug

      Hey dude… this is the first post after days of researching that made any sense regarding my ph situation at present.

      Have 300 gallon holes with soil with the recommended( jorge Cervantes mix) of 8 to 10 lbs of Dolomite and also 8 to 10lbs of Gypsum.

      drenching a sample and testing the run off and wet soil itself seems to avg at about 6.1

      plants are and have been growing well…n ground since feb 15 (cloned in nov previously and kept in pot util outdoor planting date.well conditioned to daily sunlight since birth)
      now large and bushy hundreds of branch shoots due to training/supercropping and a few pinchings early on. also have a light on each to regulate the outdoor photoperiod.

      problem is…. even through growing nice in size they all have symptoms often associated with ph problems. necrotic hooked up dry tips at leaf ends. some yellowing along leaf edge, some slight cupping which I do not believe is from any light or heat stress,

      Its been showing these signs for the last month and I did not freakout as I figured it was still growing strongly and it would balance out. Alas it isn’t.

      I see that my water is in the high 4 to mid 5 range. I thought/think this was/is the problem. The soil has mucho calcium and magnesium . It will read close to 7 when dryish and 6.1 when saturated with my water which is one day old tap to let v.o.c’s evaporate away.

      I know these leaf conditions are but symptoms of the real problem which at present I cant make heads or tails of.
      Any suggestions…wisdom???

    • Anonymous

      Judging from the way you write sentences, I would say your the real idiot.

      • Anonymous

        “Judging from the way you write sentences, I would say your the real idiot.”

        Unnecessary comma and “your” instead of “you’re”.

        Pot, meet kettle.

  • sammy quintana

    I’ve been growing pot for YEARS. STARTED WITH Plain dirt…moved to Oregon and went completely Hydro. I guess I lost my touch with dirt farming, because now I’m having some SERIOUS ISSUE with something …I’d guess it’s this fucking cheap-assed water in Buellton.
    struggling seriously going back to dirt. I started this years Ladies in FoxFarm™ but there is still something WRONG …HERE?
    HELP, if you can?

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