Is Clay Soil Acidic or Alkaline? [Soil pH Range Explained]

is clay soil acidic or alkaline

When you first venture out into your garden, there is one important question you will need to ask, what kind of soil do I have? This will determine what plants you grow and what soil additives you might need to use to adjust them.

Now, for today, we will focus on clay soil, as this is a common soil type that can cause a whole host of problems. The first and most important thing you need to know is if clay soil is acidic or alkaline.

Clay soil is alkaline with a pH level between 8-10.

Soil pH is a key element of gardening that we, as gardeners, need to get figured out. It affects everything from how your plants absorb nutrients to how strong and lush they have the potential to grow, so nailing it could change your garden completely.

This article is going to delve into what soil pH means, explore what pH level clay soil has, and how to control it.

Grow Your Yard Tip
Is your soil pH too high? Find out how to lower it here.

What is Soil pH?

Before we figuratively dive into the pH level of clay soil, we should quickly explain what pH levels actually mean.

The pH level is a scientific scale that measures the acidity or alkalinity of a substance, including soil. This scale ranges from 0-14.

Let’s look at what pH levels different soil types have.

Soil Type pH Level
Clay Alkaline Over 7
Loamy Neutral 7
Sandy Acidic Under 7

The best way to test the pH level of your soil is to buy a soil testing kit. These are very easy to use and can be picked up relatively affordably online or from a garden store. This will give you a clear indication of what kind of soil you are dealing with, so you can make your next move.

The pH level of the soil is important because it affects the plant’s ability to absorb nutrients and dictates what plants you can grow in the soil you have available.

For instance, blueberries and rhododendrons will not tolerate alkaline soils at all. This is an important fact to keep in mind when you are planning your garden.

Is Clay Soil Alkaline or Acidic?

Clay soil has a pH level between 8-10, which is strongly alkaline.

Many plants may have trouble growing in clay soils for two reasons.

The first is because clay has high water retention and poor drainage. The second is that the pH level is too high to allow for proper nutrient absorption.

The ideal pH for most soil is between 5 and 7, as this will achieve the best potential for nutrient absorption.

For both these reasons, you will need to deploy some soil additives to make the soil more accommodating for a wider variety of plants. The most effective methods will both lower the pH and improve the soil texture at the same time.

Grow Your Yard Tip
Soil pH needs to be at the correct levels to absorb nutrients like phosphorus and nitrogen. Find out how to maximize nutrient uptake in our deep dives into these nutrients.

How to Lower Your Soil pH Range

While some plants flourish in alkaline soils like clay, they are few and far between. This is why we suggest trying out some simple techniques to improve your soil quality.

The best time to try these soil adjustments is before you plant any ornamentals rather than after the plants have established themselves. However, if this is not possible, they will still work, just a little slower.

Here are three ways to lower the pH of your clay soil:

Aluminum Sulphate

A quick way to lower your soil pH is by using aluminum sulfate.

This is a soil additive that you can pick up at any garden store. We prefer this version because it is very soluble, but you can also use elemental sulfur if you want to be more economical.

DON’T MISS: Why does soil become acidic in the first place? Find out here!

Organic Matter

To loosen the soil up and improve drainage, we suggest using some form of organic material. This is also a relatively cheap option because you can make your own at home.

Manure, compost, peat moss, wood ash, and pine needles are all great options for this job.

Coffee Grounds

Coffee grounds are one of those valuable pieces of kitchen waste that should never end up in your trash!

They are highly acidic and relatively fast-acting if added straight to your soil. Alternatively, you can add the grounds to your compost heap whenever you empty the pot so your compost will benefit from their acidity.

Plants That Love Clay Soil

After saying all that, there are some plants that absolutely thrive in clay soil. If your soil is proving challenging to adjust, then we recommend planting some of these species that will enjoy its current conditions.

Common plants that like clay soil are:

  • Apple trees
  • Hydrangeas
  • Lavender
  • Peonys
  • Roses
  • Sunflowers
  • Turfgrass

Frequently Asked Questions:

Does clay soil need lime?

Lime can be beneficial to so many soil types, but clay is not one of them.

Since clay soil has such a high pH level, liming your soil will be ineffective because it is mainly used for raising your soil pH. We suggest using lime if you have loamy or sandy soils that have a pH level below 7.

What is the best fertilizer for clay soil?

We recommend using natural fertilizers like manure, compost, or peat moss instead of a granulated or liquid fertilizer, which will not effect the soil texture.

These organic materials will loosen up the soil and add vital nutrients to help plants thrive.

Can you put topsoil over clay?

This is an option, especially if you want to plant a lawn and the clay soil is getting in the way.

We suggest adding at least 6-inches of topsoil on top of the clay for it to be effective. Adding one of the soil amendments we suggested will also be beneficial to add before you lay down the top soil.


Clay soil can be useful in many ways, but the pH level is something that you may need to adjust.

Clay soil is alkaline, so it has a high pH level. Luckily, this can be easily lowered using the methods we have outlined above. Lowering the pH will improve the soil quality and assist with nutrient uptake so it is more accommodating for more plant types.

We hope this has helped you get to the bottom of the soil in your garden and given you some useful tips and tricks to dealing with alkaline clay soil.

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