How can I raise or lower the pH of my soil mix?

Advanced Techniques GrowFAQ
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Contributed by: Dowzer Submitted: June 23, 2003

How can I raise or lower the pH of my soil mix?

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)

1. 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.

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

3. 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.

    by MisterIto
    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.

    by MisterIto
    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.

    Contributed by: Spiritual.Fa
    23-08-2003

    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

    Other Benefits of Dolomite Lime

    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.

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