What Is Ericaceous Compost? (Plus What To Grow With It)


Do you grow certain acid-loving plants, such as azaleas, blueberries, and hydrangeas in your garden?  If so, then you may have heard that you should use ericaceous compost to help these plants to grow.

If you are wondering what ericaceous compost is, what it does, and why to use it, then you’ve come to the right place.

So, what is ericaceous compost?  Ericaceous compost is acidic compost, meaning it has a pH below 7.0.  Ericaceous compost is used to encourage growth of acid-loving plants that need acidic soil to grow well.

Of course, before you go about using ericaceous compost in your garden, it is important to understand why certain plants need it.  We’ll get into why you should use ericaceous compost, along with how to make your own ericaceous compost.

First, though, we’ll take a closer look at what ericaceous compost is.

What is Ericaceous Compost?

Ericaceous compost is used to feed plants that need acidic soil to grow well.  This includes acid-loving plants such as azaleas and blueberries, which grow poorly in alkaline soil.

blueberries
Acid-loving plants, such as blueberries, grow well in acidic soil. You can use ericaceous compost to acidify your soil.

Ericaceous compost can also help to acidify soil so that you can get blue flowers on certain varieties of hydrangeas (more on this later).

Ericaceous compost has a pH below 7.0, meaning that it is acidic.  When soil is acidified using ericaceous compost, certain nutrients in the soil will become available to plants in the proper amounts.

When a nutrient in the soil is available, it means that a plant can absorb the nutrient through its roots.  If the soil pH is too high or too low, the nutrient will be unavailable, meaning that a plant cannot absorb the nutrient through its roots.

With a pH that is too high or too low, nutrients can become unavailable to plants even if there is plenty of that nutrient in the soil.

For more information, check out this chart from Research Gate, which gives a good visual of the relationship between soil pH and nutrient availability.

As you can see from the chart, there are certain elements (such as iron, manganese, boron, and zinc) that become more available as soil pH drops below 7.0 (that is, when the soil becomes more acidic).

One important thing to note is that a small difference in pH makes a big difference to plants.  For example, a soil pH of 6.0 means that the soil is 10 times as acidic as a soil with a pH of 7.0.  A soil pH of 5.0 means that the soil is 100 times as acidic as a soil with a pH of 7.0.

For more information, check out this article on soil pH from the Michigan State University Extension.

If soil pH is too high (or too low), some plants will suffer from nutrient deficiencies due to unavailability of nutrients in the soil.  Nutrient deficiencies will present clear symptoms, such as when your plants develop chlorosis (yellow leaves), poor growth, and other problems.

iron chlorosis
If soil pH is too low or too high, nutrient deficiencies can occur. One symptom is chlorosis, or yellowing of leaves.

The best way to tell if your soil pH is in the proper range is to get a soil test.  You can do a soil test yourself with a home test kit.

These home test kits are available online or at garden centers.  However, they are often not as precise as laboratory soil tests.

For more information, check out my article on how to do a soil test.

You can also send a soil sample away to your local agricultural extension service to have it tested for a nominal fee.  They will send you results, including soil pH and levels of nutrients including the big three (NPK, or nitrogen, phosphorus, and potassium), along with other information.

For more information, check out my article on what a soil test tells you.

There is another benefit of ordering a laboratory soil test.  If you tell them what plant you are growing, they will send recommendations for soil treatments and amendments, along with the soil test results.

How Long Does Ericaceous Compost Last?

Ericaceous compost may last for a long time (possibly years), depending on what materials are used to make it.  For example, peat moss resists compaction, and can last for many years in the soil.

For more information, check out this article on peat moss and compost from the University of Vermont Extension.

sphagnum moss
Peat moss lasts a long time in the soil, since it resists compaction.

Be careful about adding anything to your soil without knowing the pH and nutrient levels beforehand!  Adding too much acid to your soil at once can harm your plants.  Even worse, you may end up needing to add lime or other amendments to raise the pH back to an acceptable level.

As mentioned earlier, the best way to determine if you need to add ericaceous compost (or any other additive) to your garden is by doing a soil test. 

What Will Grow in Ericaceous Compost?

The best plants to grow in ericaceous compost are acid-loving plants, which grow better in acidic soil with a lower pH.

Check out the table below for some common acid-loving plants and their ideal soil pH range.

PlantIdeal Soil
pH Range
Azaleas4.5 to 5.5
Blueberries4.5 to 5.5
Cranberries4.0 to 5.0
Grapes5.5 to 6.5
Hydrangeas
(blue flowers)
5.0 to 5.5
Rhododendrons4.5 to 5.5

Most vegetable gardens require a pH range of 6.0 to 7.0.  All of the acid-loving plants in the table above would do well in soil with a pH of 5.0, which is, on average, 10 to 100 times as acidic as ordinary garden soil!

As such, you should keep a dedicated area of your garden for growing acid-loving plants.  That way, you can use ericaceous compost in that area only, to keep the pH low (around 5.0).

For more information, check out this article from the Cooperative Extension on modifying soil pH for blueberries & other plants.

Do Blue Hydrangeas Need Ericaceous Compost?

Certain varieties of hydrangeas, (such as mophead and lacecap hydrangeas) require acidic soil with a pH of 5 to 5.5 in order to produce blue flowers.  When grown in acidic soil, they will produce pink flowers instead.

hydrangea flower
Blue hydrangeas need soil with a pH between 5.0 and 5.5 to grow blue flowers.

You can use ericaceous compost on the hydrangeas mentioned above to acidify the soil and bring the pH into the proper range to produce blue flowers. – for more information, check out this artile from Thompson-Morgan.

However, remember that not all hydrangeas are capable of producing different colored flowers.  For example, white hydrangeas cannot change their flower color.

For more information, check out this article from Hydrangea Guide.

Can I Use Ericaceous Compost for Normal Plants?

Yes, you can use ericaceous compost for normal plants.  However, keep an eye on the soil pH when you do so.  As mentioned above, most “normal” plants need a soil pH between 6.0 and 7.0, so adding too much ericaceous compost can make the pH too low.

This can lead to nutrient deficiency in your plants due to unavailability.  To avoid this, you can add some lime (calcium carbonate) or dolomitic lime (calcium and magnesium carbonate) to your soil along with ericaceous compost.

The lime will raise pH, offsetting the acidifying effect of the ericaceous compost.  Of course, you can also mix the ericaceous compost with neutral-pH compost to make a less acidic mixture.

Can You Make Ericaceous Compost?

Yes, you can make your own ericaceous compost.  It is just like making normal compost, except that you want the resulting mixture to have a lower pH.

This means that you still want to start by adding ordinary yard waste and kitchen scraps to your compost pile.  However, you need a way to acidify the mixture so that it is suitable for acid-loving plants.

Ericaceous compost still requires ordinary composting material, such as grass clippings, fallen leaves, and food scraps.

There are many ways to lower the pH of soil or compost.  One way to do this is to add elemental sulfur, which has a yellow appearance.

According to the Iowa State University Extension, you should add no more than 2 pounds of sulfur per 100 square feet of soil.  Sulfur takes time to work, so wait at least a few months before retesting your soil pH.  You don’t want to add more sulfur and end up with compost that is too acidic!

sulfur
Sulfur is a soil amendment that will acidify soil or compost (lower pH).

Some other sulfur-based amendments that will acidify your soil are aluminum sulfate and iron sulfate.  These two amendments lower soil pH faster than pure elemental sulfur.  However, overuse of these soil amendments can result in too much iron or aluminum in your soil, so be careful.

For more information, check out my article on how to make your garden soil more acidic.

Where Can I Buy Ericaceous Compost?

To find soil acidifiers, try these brands, which are approved for organic gardening:

If you simply want to acidify your own soil or compost mixture, then check out these sulfur pellets on Amazon.

Conclusion

By now, you have a much better idea of what ericaceous compost is and when you should use it in your garden.  You also know how to make your compost or soil more acidic if necessary (always do a soil test first to make sure!)

I hope you found this article helpful – if so, please share it with someone who can use the information.  If you have any questions about ericaceous compost, please leave a comment below.

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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