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Adjusting Soil pH

Add peat moss to lower soil pH
Add peat moss to lower soil pH
Add peat moss to lower soil pH

The results of a soil pH test will indicate how acid or alkaline your soil is. Organic soil amendments are the best way to adjust soil pH. Adjusting soil pH is not an exact science and takes time.

A pH test number that is more than 0.5 on either side of the optimal pH number for the plants you want to grow will require a soil amendment or additive to adjust the pH. A pH test number that is within 0.5 of the optimal pH number for the plants you want to grow does not require soil amendments.

The quickest way to change pH is to add either agricultural sulfur (powdered sulfur, aluminum sulfate, or iron sulfate) to make alkaline soils more acid or agricultural ground limestone to make acid soils more alkaline. The best long-term way to improve soil pH is to add other slower, but longer acting organic materials (see the lists below).

The amount of additives or amendments necessary to correct soil pH varies according to soil texture. Sandy soil requires the least amount of additive, loamy soil a bit more, and clay soil the most. To determine the texture of your soil, wet a bit of garden soil and rub it between your fingers; if the soil feels gritty it is sandy; if it feels smooth like flour it is loamy or silty, if it feels sticky or slippery it has high clay content.

If you are adding agricultural sulfur or ground limestone to your garden, follow the recommended application rate listed on the package or bag. The amount will vary according to the type of soil in your garden and the number of square feet you are amending.

After adding sulfur or limestone or any soil additive to your garden re-test the soil in 40 to 60 days. Expect small changes to the pH—0.5 to 1 unit at most. Allow at least five or six weeks between the applications of soil amendments. Work steadily towards achieving the pH that will be ideal for plants you want to grow. Changing the soil pH by one unit each year is reasonable.

A good time to begin adjusting soil pH is in the Fall; check the progress again in the Spring. If you begin the process in Spring, start early–at least three weeks before planting. This will allow soil additives to begin to break down and start working. Check the soil pH regularly—twice a year is ideal.

Organic materials to adjust soil pH:

 

Adjusting Alkaline Soil:

The best way to lower soil pH to neutral 6.0 to 7.0 is to add naturally acidic organic materials:

  • Aged sawdust
  • Wood chips
  • Leaf mold
  • Peat moss
  • Cottonseed meal
  • Pine needles
  • Coffee grounds
  • Fresh manure
  • Oak leaves
  • Ground up oak bark
  • Pine needles

If your garden is in a region of low rainfall, a high pH could be the result of accumulated salts. Flush salts below the root zone of sensitive plants such as beans, carrots, onions, and peppers by watering regular non-saline water. Also add compost, mulch, or leaf mold.

The best time to correct soil alkalinity is in the Fall; that will allow organic materials time to decompose (organic materials tie up nitrogen while decomposing).

Adjusting Acid Soil:

To raise soil pH of acid soil is add any of these long-acting organic materials:

  • Bonemeal
  • Ground clamshells
  • Ground eggshells
  • Ground oyster shells
  • Hardwood ashes
  • Fine-ground agricultural lime: dolomitic lime (if the soil test reveals a magnesium deficiency) or calcitic lime (if the soil test reveals a calcium deficiency). The general guidelines for applying limestone to increase pH by one unit across 100 square feet: 3 pounds of sandy soil; 5 pounds on sandy-loam; 7 on loam; and 8 pounds on clay soil.

The best time to correct soil acidity is in the Fall. If you want to correct soil acidity in the Spring do as at least three weeks before planting; that will allow time for soil additives to begin to work.

Related Articles:

Understanding Soil pH

How to Test Your Soil

 

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11 Comments

    • Correct the soil pH at the end of your growing season–allow rain or irrigation to carry your soil amendments deep into the soil. Adding aged compost to the growing beds on a regular basis will also modify your soil pH over a period of a year or two.

  1. My soil is very acidic because of all the Pine and Oak trees it also has very little calcium. It’s really virgin soil nothing has ever been grown on it. Of all the different plants and vegetables I grow not much does very well. My tomatoes did better last year because I added bone meal. I get a lot of Bloom rot. Egg plants don’t do well at all or pumpkins.
    Any suggestions would be greatly appreciated. darlinmiller1492@gmail.com

    • If your ground has not been planted with vegetables in the past, you may want to double dig your planting beds the first year out — that is turn the soil to 24 inches deep– and add lots of aged compost or organic planting mix. Aged compost will in a year or two bring the soil pH closer to neutral. Aged compost or commercial organic planting mix will be rich in all of the nutrients vegetables need. As well, you can add a half handful or organic fertilizer to the bottom of planting hole or sprinkle on seedbed (use 5-10-10).

  2. Avoid adding aluminum sulphate. It is toxic and enough will kill EVEN BLUEBERRIES! Iron sulphate is a naturally occurring mineral which can be used to reduce pH for all acid-loving plants. It’s not expensive to use, keeps well, and adds iron to green-up grass, etc.

  3. I just fact-checked Christa; aluminum sulfate is definitely a questionable thing to add to soil. It’s nastier than sulfur, anyhow.

    I’d also say: don’t add minerals to adjust the ph of sandy soils unless you’ve already dumped on the organic matter (or are growing cacti, I suppose). You need organic matter to grow most things people want to grow, if your soil is real “poor” and sandy. (Lots of other uses for sand though.)

  4. Use 50% coral sand and 50% Perlite ….do not add compost….plant seedlings, then sprinkle worm castings at each plant, then cast dead leaves / compost on the surface of the ground; Do not till the dead matter into the ground….they’ll decompose and provide nutrients to filter downward…..I learned the hard way!

  5. Be sure to wash out all the woody / dead material of small starter seedlings at Home Depot / Lowes before planting…the root systems of these seedlings are fragile but transplanting is fun! Sprinkle either dolomite lime or acidifier at each particular planting according to each plant preference of PH…….I learned the hard way!

  6. Use a half-filled pail of water and immerse the 2 x 2 seedling starter you got from Home Depot…swish the whole seedling around in the water…use some common sense….the roots are fragile so cradle the seedling in your palm ..don’t dangle the plant with wet roots although you’ll find the root connection pretty strong…be sure to remove bits of wood and most of the soil….takes 15 seconds…take a trowel and cleave a cut into the sandy / perlite mix way deep and dangle the roots in….sprinkle worm casting around the surface / on the plant and water;
    All my comments are deduced from Gary of Laguna Hills Nursery in California; He can be viewed at: https://www.youtube.com/watch?v=ISX7VMW4LFQ
    Thanks to him for solving all my preconceived notions of how to cultivate a avocado…..

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