Clay soil pH levels can run from 5.0 to 7.5. If you're planting vegetables, the pH should be between 6.5 and 7.0, since most veggies love acidic soil. A reading of 7 is interpreted as a neutral soil pH. Any pH reading that's above 7 is alkaline.
Soils with a high proportion of clay or organic matter have a larger number of surface sites able to hold hydrogen ions and are able to resist a decrease in pH. However, once acidic, highly buffered soils are able to resist an increase in pH.
One way of improving the texture of a clay soil is to add lime. This raises the pH of acid clay soils, making them more alkaline and in doing so it encourages clay particles to stick together in small clumps. This results in larger particles and makes the soil more friable and easier to work.
To acidify clay soil, add ingredients like sulfur or iron sulfate. These products are easy to add; they are simply distributed at surface level and watered in. Sulfur can not only increase the acidity but will help to break up the compaction that occurs in clay soil.
In nature, sand typically has a lower pH than clay since water (rain) moves through sand faster than clay.
), and normally falls between 3 and 10, with 7 being neutral. Acid soils have a pH below 7 and alkaline soils have a pH above 7. Ultra-acidic soils (pH < 3.5) and very strongly alkaline soils (pH > 9) are rare.
Soil pH can be reduced most effectively by adding elemental sulfur, aluminum sulfate or sulfuric acid. The choice of which material to use depends on how fast you hope the pH will change and the type/size of plant experiencing the deficiency.
Vinegar can be used as a natural substance to break down clay soils. The vinegar's acidity will help dissolve some of the clay particles in the soil. This will make it easier for water and air to move through the soil and make it less dense.
Amending your soil properly can overcome heavy, compacted clay and get it back on track for healthy lawn and garden growth. Adding materials such as organic compost, pine bark, composted leaves and gypsum to heavy clay can improve its structure and help eliminate drainage and compaction problems.
Even if you don't have acid-loving plants, coffee grounds in smaller amounts break down quickly and add a great source of nitrogen for all your vegetables. It can also be used to amend heavy clay soils (which is what most of our soils are in Missoula!)
Gypsum is often used on heavy clay soil in particular, as it breaks down the compacted matter. Unlike sand, which can actually harden clay, gypsum makes it crumbly.
Organic matter is one of the key ingredients in amending a clay soil. Organic matter helps with drainage as well as adding nutrients and improving the soil's texture. A great source of organic matter is composted chicken manure pellets (Super Booster, Blood & Bone Plus or Super Growth).
Citrus prefer a sandy or loam soil. They will tolerate clay soils providing they are planted on a raised bed with lots of compost mixed into the soil. Dig in Organic Compost or peat to help break up clay soils and improve water-holding capacity of light sandy soils.
What are the Disadvantages of Clay Soil? Clay soil can be very heavy and difficult to work with, especially when wet. Moreover, because this soil often suffers from poor drainage this is frequently the case. Clay soil can also be compacted easily, so you should avoid walking on it whenever possible.
Ways to improve the quality of clay soil
Lots of organic matter – such as spent mushroom compost, well-rotted farmyard manure, homemade compost – will add nutrients to the soil and help open up the texture.
The first step is to add gypsum to the soil. Apply gypsum at 1 kilo per square metre, digging this into the top 10-15cm well. Gypsum works on the clay, breaking it up into small crumbly pieces making it easier to work with and also improves drainage.
In fact, clay soils offer plants two major advantages over other soil types: they hold water well, minimizing drought stress, and are abundant in nutrients essential for plant growth. So, if you've been struggling to achieve your dream garden or landscape in clay soil, cheer up!
Salt often exists in clay soil and it is extremely detrimental to soil structure. It can make the clay soil hard and dense by dispersing the fine clay particles that fill available air holes.
Bark, manure, leaf mold and compost are among the organic amendments commonly used to improve clay soil, Brewer noted. Applied to the soil surface, these materials form a protective blanket that slows evaporation and reduces soil hardening.
After using lime, baking soda is the best way to increase the pH in soil, plus it is one of the easiest, fastest, and most cost-effective methods. Baking soda is also a very gentle method, so you do not need to worry about harming your plants.
Manure is typically between pH 8-12, but don't expect manure to affect pH levels in soil.
Soil pH can be lowered by half a point—from 7.0 to 6.5, for example—by increasing soil nitrogen. Adding compost, manure, or organic soil amendments like alfalfa meal to the soil can help drop pH over time by increasing bacterial populations.
Two materials commonly used for lowering the soil pH are aluminum sulfate and sulfur. These can be found at a garden supply center. Aluminum sulfate will change the soil pH instantly because the aluminum produces the acidity as soon as it dissolves in the soil.